Co-reporter:Zixin Zhang, Jianxiong Tang, Heran Wang, Qinghua Xia, Shanshan Xu, and Charles C Han
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 48) pp:26400
Publication Date(Web):November 24, 2015
DOI:10.1021/acsami.5b09820
Implantation of sustained antibacterial system after abdominal surgery could effectively prevent complicated intra-abdominal infection. In this study, a simple blended electrospun membrane made of poly(d,l-lactic-co-glycolide) (PLGA)/poly(dioxanone) (PDO)/Ciprofloxacin hydrochloride (CiH) could easily result in approximately linear drug release profile and sustained antibacterial activity against both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). The addition of PDO changed the stack structure of PLGA, which in turn influenced the fiber swelling and created drug diffusion channels. It could be a good candidate for reducing postoperative infection or be associated with other implant to resist biofilm formation.Keywords: antibacterial activity; bicomponent; control release; electrospinning; intra-abdominal infections
Co-reporter:Di Jia, Javoris V. Hollingsworth, Zhi Zhou, He Cheng and Charles C. Han
Soft Matter 2015 vol. 11(Issue 45) pp:8818-8826
Publication Date(Web):08 Sep 2015
DOI:10.1039/C5SM01531F
The state transition from gel to glass is studied in a biphasic mixture of polystyrene core/poly(N-isopropylacrylamide) shell (CS) microgels and sulfonated polystyrene (PSS) particles. At 35 °C, the interaction between CS microgels is due to short-range van der Waals attraction, while that between PSS particles is from long-range electrostatic repulsion. During the variation of the relative ratio of the two species at a fixed apparent total volume fraction, the mixture exhibits a gel-to-defective gel-to-glass transition. When small amounts of PSS are introduced into the CS gel network, some of them are kinetically trapped, causing a change in its fractal structure, and act as defects to weaken the macroscopic gel strength. An increase of the PSS content in the mixture promotes the switch from the gel to the defective gel, e.g., the typical two-step yielding gel merges into one-step yielding. This phenomenon is an indication that inter-cluster bond breakage coincides with intra-cluster bond fracture. As the relative volume fraction of PSS exceeds a critical threshold, the gel network can no longer be formed; hence, the mixture exhibits characteristics of glass. A state diagram of the biphasic mixture is constructed, and the landscapes of the different transitions will be described in future studies.
Co-reporter:Junhua Luo, Guangcui Yuan, Chuanzhuang Zhao, Charles. C. Han, Jie Chen and Yun Liu
Soft Matter 2015 vol. 11(Issue 12) pp:2494-2503
Publication Date(Web):05 Feb 2015
DOI:10.1039/C4SM02165G
In this study, mixed suspensions of large hard polystyrene microspheres and small soft poly(N-isopropylacrylamide) microgels are used as model systems to investigate the static and viscoelastic properties of suspensions which go through liquid to gel transitions. The microgels cause short-range attraction between microspheres through the bridging and depletion mechanism whose strength can be tuned by the microgel concentration. Rheological measurements are performed on suspensions with the volume fraction (Φ) of microspheres ranging from 0.02 to 0.15, and the transitions from liquid-like to solid-like behaviors triggered by the concentration of microgels are carefully identified. Two gel lines due to bridging attraction under unsaturated conditions are obtained. Ultra-small angle neutron scattering is used to probe the thermodynamic properties of suspensions approaching the liquid–solid transition boundaries. Baxter's sticky hard-sphere model is used to extract the effective inter-microsphere interaction introduced by the small soft microgels. It is found that the strength of attraction (characterized by a single stickiness parameter τ) on two gel lines formed by bridging is very close to the theoretical value for the spinodal line in the τ–Φ phase diagram predicted by Baxter's model. This indicates that the nature of the gel state may have the same thermodynamic origins, independent of the detailed mechanism of the short-range attraction. The relationship between the rheological criterion for the liquid–solid transition and the thermodynamic criterion for the equilibrium–nonequilibrium transition is also discussed.
Co-reporter:Qinghua Xia, Ziwen Liu, Chenhong Wang, Zixin Zhang, Shanshan Xu, and Charles C. Han
Biomacromolecules 2015 Volume 16(Issue 9) pp:
Publication Date(Web):August 25, 2015
DOI:10.1021/acs.biomac.5b01099
Placing a physical barrier between the injured site and the adjacent tissues is a very common and highly effective approach to prevent abdominal adhesions in these days. A biodegradable trilayered barrier was fabricated to prevent formation of abdominal adhesions, in which a poly(lactide-co-glycolide)/poly(lactide)-b-poly(ethylene glycol) (PLGA/PLA-b-PEG) electrospun layer was sandwiched between layers of carboxymethyl chitosan (CMCS) sponge. The hydrophilic CMCS sponge layers with glycerin (GL) could adhere to the surface of wound easily, and present great hemostatic capability. The mechanism of the formation of adhesion related to blood clots acting with fibroblast cells was evaluated in detail. The blood clot acted as a “medium” inducing the fibroblast cells growth and proliferation, but had no special attraction on epithelial cells. CMCS sponge layer took away the blood clots during the swelling and dissolution stages. The electrospun layer promoted the growth of epithelial cells, but exhibited inhibition on the adhesion and spread of fibroblast cells, which ensured excellent effect of adhesion prevention. Evaluated by a rat model of sidewall defect-bowel abrasion, significant reductions of postoperative adhesion in its level and occurrence were observed in animals treated by the trilayered barrier.
Co-reporter:Zhiyuan He, Yongri Liang, Wenhong Yang, Hideshi Uchino, Jiangang Yu, Wen-Hua Sun, Charles C. Han
Polymer 2015 Volume 56() pp:119-122
Publication Date(Web):15 January 2015
DOI:10.1016/j.polymer.2014.11.061
A series of random hyperbranched linear polyethylene (RHBLPE), which represents a completely new type of polyethylene, was synthesized through a single step polymerizing process of ethylene by an α-diiminonickel complex pre-catalyst. The molecular weights, branching architectures, chemical compositional distributions as well as the crystallization behavior of these RHBLPEs were carefully investigated by GPC, NMR, A-TREF and DSC, respectively. The tensile properties and elastic recoveries at different temperatures were also explored. Moreover, their distinct elastomeric properties at different temperatures were observed and charactered. It has been determined that these properties are mainly affected by the crystallization behavior of RHBLPEs. The crystallization structures of these RHBLPEs were manipulated through the polymerization temperatures of the ethylene. Thus the elastic properties of RHBLPEs could be tailored to meet different application demands at wide temperature range (−20 to 65 °C).
Co-reporter:Ming-ji Wang;Guang-cui Yuan 袁光萃 韩志超
Chinese Journal of Polymer Science 2015 Volume 33( Issue 4) pp:652-660
Publication Date(Web):2015 April
DOI:10.1007/s10118-014-1475-0
The influences of hyperbranched polyethylenimine (hPEI), which possesses many reactive amino end-groups, on the blending properties of bisphenol-A polycarbonate (PC) and amorphous polyamide (aPA) were systematically investigated. Scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were used to observe the effect of hPEI on morphologies of PC and aPA phases in bulk blends. While the interfacial fracture toughness between planar PC and aPA layers with and without hPEI was studied by using augmented double cantilever beam (ADCB) method. Results show that the compatibility in PC/aPA blends can be significantly improved by adding a small amount of hPEI, mainly due to the interchange reactions between the polymers leading to the formation of block copolymers, cross-linked polymers and molecules with other constitutions. The augmented double cantilever beam experiments showed that the reactive process drastically reinforced the interfacial adhesion between planar layers of PC and aPA. However, degradation takes place during annealing at 180 °C, which was responsible for the production of small molar mass species of PC.
Co-reporter:Jingjing Yang, Yongri Liang, Charles C. Han
Polymer 2015 Volume 79() pp:56-64
Publication Date(Web):19 November 2015
DOI:10.1016/j.polymer.2015.09.067
•Effects of Tc,PLLA on the interactive crystallization behaviors of the PLLA-b-PEG copolymer were studied.•Tc,PLLA greatly affected the crystalline microstructure and the confined crystallization behavior of PLLA-b-PEG copolymer.•The following PEG crystallization would modify the stability of PLLA crystals and this influence was dependent on Tc,PLLA.Crystallization behaviors of crystalline–crystalline diblock copolymers are important in understanding the structure evaluation. In this work, we investigated effects of crystallization temperature on the interactive crystallization behavior of crystalline–crystalline diblock copolymer of poly(l-lactide)-block-poly(ethylene glycol) copolymer (PLLA-b-PEG) with differential scanning calorimetry (DSC), polarized optical microscopy (POM), atomic force microscopy (AFM), small and wide angle X-ray scattering (SAXS/WAXS) and Fourier transform infrared (FTIR) spectroscopy techniques. SAXS results showed that during the two-step crystallization process PEG blocks should crystallize within spaces from interlamellar or interfibrillar of PLLA crystals, and the microstructure formation in PLLA-b-PEG copolymer was greatly dependent on TC,PLLA (crystallization temperature of PLLA). Moreover, crystal nucleation and crystallization rate of PEG blocks were also dependent on Tc,PLLA. On the other hand, almost reversible crystalline structure changes of PLLA crystals was induced by crystallization and melting of PEG blocks. And the extent of crystalline structure change of PLLA blocks by PEG crystallization was increased with Tc,PLLA increasing.
Co-reporter:Chenhong Wang, Kuo Zhang, Heran Wang, Shanshan Xu, Charles C. Han
Polymer 2015 Volume 61() pp:174-182
Publication Date(Web):20 March 2015
DOI:10.1016/j.polymer.2015.02.001
•Highly porous structure facilitated the diffusion of soluble degraded products.•The structural integrity and the fibrous morphology were well maintained.•The electrospun PDLGA/PDLA-b-PEG scaffolds had good biocompatibility in vivo.•The electrospun PDLGA/PDLA-b-PEG scaffolds degraded faster in vivo than in vitro.•Faster degradation rate in pigs than in rats was observed.Study of the degradation behavior of implants is of crucial importance in biomedical fields before practical applications. In this study, degradability of poly (DL-lactic-co-glycolic acid) (PDLGA)/poly (DL-lactide)-block-poly (ethylene glycol) (PDLA-b-PEG) scaffolds was evaluated both in vitro and in vivo. In vitro degradation of fibrous scaffolds showed that highly porous structure facilitated the diffusion of soluble degraded products out of the scaffolds. The electrospun scaffolds could maintain the structural integrity and the fibrous morphology in vitro for 8 weeks and during the wound healing process in vivo. When implanted in vivo, the scaffolds had good biocompatibility and degraded faster than in vitro. Long term study of degradation in rats showed that the scaffolds were totally degraded and absorbed. Faster degradation in pigs than in rats might due to the surgical condition and difference of physiological environment between rats and pigs, such as wound area, hemorrhage, the local motion and inflammatory reaction. The interaction between the scaffolds and the surrounding tissues would also influence the degradation of the implants.
Co-reporter:Zhi Zhou, Javoris V. Hollingsworth, Song Hong, Guangmin Wei, Yu Shi, Xi Lu, He Cheng and Charles C. Han
Soft Matter 2014 vol. 10(Issue 33) pp:6286-6293
Publication Date(Web):16 Jun 2014
DOI:10.1039/C4SM01181C
A series of microgel particles composed of a polystyrene (PS) core and a thermo-sensitive poly(N-isopropylacrylamide) (PNIPAM) shell with different shell thicknesses were investigated to elucidate the effect of microgel softness on its shear thickening behavior. Since the softness of the microgels increases with decreasing temperature through the volume phase transition effect of PNIPAM shell, the measured softness parameter, n, which is derived from the Zwanzig–Mountain equation, was used to measure and describe the combined influences of temperature and shell thickness. Confocal microscopy is used to investigate the interaction potential between microgel particles with different softness parameters. According to the obtained results, the softness parameter can provide an estimate for the shear thickening behavior of microgel suspensions, at least semi-quantitatively.
Co-reporter:Chuanzhuang Zhao, Guangcui Yuan and Charles C. Han
Soft Matter 2014 vol. 10(Issue 44) pp:8905-8912
Publication Date(Web):10 Sep 2014
DOI:10.1039/C4SM01798F
Gelation and glass transition in a mixed suspension of polystyrene (PS) microsphere and poly(N-isopropylacrylamide) (PNIPAM) microgel were studied as a function of the total colloid volume fraction and mixing ratio of these two components. The PNIPAM microgel, which is adsorbable on the PS microsphere surface, can induce bridging or stabilizing effect between microspheres depending on whether the volume fraction of microgel (ΦMG) is smaller or larger than the saturated adsorption concentration (Φ*MG) for a given volume fraction of the microsphere (ΦMS). Φ*MG is in a linear relationship with ΦMS, and the value of ΦMG/Φ*MG can be taken as an approximate measure of surface coverage. A state diagram of gelation and glass transition is constructed with the short-ranged attractive interaction, resulting from the well-defined bridging bonding. Keeping ΦMG/Φ*MG = 0.20 and increasing ΦMS from 0.25 to 0.55, the mixed suspension transforms from a bridging gel into an attractive glass; moreover, while keeping ΦMS = 0.45 and increasing ΦMG/Φ*MG from 0.20 to 1.2, the mixed suspension changes from a bridging gel into an attractive glass, and then to a repulsive glass. The bridging effect and the cage effect can be distinguished by the yielding behaviors in rheological measurements. In the nonlinear dynamic rheological experiments, one-step yielding, corresponding to the disconnecting of bridge network, is observed in the bridging gel, and one-step yielding, corresponding to the breaking of cage, is observed in the repulsive glass. However, a two-step yielding behavior is found in the bridging-induced attractive glass, which is attributed to the bridging effect of microgels and the caging effect of the dense environment.
Co-reporter:Weichao Shi, Wei Liu, Jian Yang, Zhiyuan He and Charles C. Han
Soft Matter 2014 vol. 10(Issue 15) pp:2649-2655
Publication Date(Web):13 Jan 2014
DOI:10.1039/C3SM52713A
Coarsening is a general phenomenon in phase separating mixtures. In this study, we report a hierarchical coarsening at different length scales. Dispersed domains grew by direct combination of two/three small ones while some small domains can survive for a long time. The small angle laser light scattering showed that the scattered intensity exhibited multiple “decay–growth” transitions in the coarsening process. The evolution of the main peak gave a characteristic power law index of about −3/4, which is much faster than the −1/3 relationship from the traditional theories. We propose that relaxation and hydrodynamic flow play important roles in this process.
Co-reporter:Jing Jin;Jiang Du;Hongyu Chen;Gary March;Kim Walton
Journal of Applied Polymer Science 2014 Volume 131( Issue 19) pp:
Publication Date(Web):
DOI:10.1002/app.40863
ABSTRACT
This study mainly focuses on the formation of isotactic polypropylene (iPP) blend morphologies with microspheres and distinct bead–string spherulites. iPP microspheres have been prepared by a simple and convenient strategy through either an isothermal or a nonisothermal crystallization process based on the macrophase-separated structure in molten state of iPP/olefin block copolymer (OBC) blend. The dimension of the iPP spheres can be adjusted easily from about 1 µm to >10 µm by controlling the compatibility and annealing conditions. It was found that any of the following three parameters, the molecular structure of OBC (particularly the octene content), molecular weight of iPP, and annealing condition can be rescaled with others in controlling the dimension of the iPP microspheres. The mechanism of the formation of iPP microspheres was studied in detail. Surprisingly, the typical spinodal decomposition morphology with interconnected or thin sheet structure is the precursor of these microspheres. During the subsequent annealing process, it breaks up and further coarsens into spherical structure. In addition, distinct spherulites with a bead–string substructure have been obtained during the isothermal crystallization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40863.
Co-reporter:Wenjie Du, Guangcui Yuan, Mingji Wang, Charles C. Han, Sushil K. Satija, and Bulent Akgun
Macromolecules 2014 Volume 47(Issue 2) pp:713-720
Publication Date(Web):January 7, 2014
DOI:10.1021/ma401895t
Interfacial evolution of deuterated polycarbonate (dPC) and poly(methyl methacrylate) (PMMA) bilayer films supported on silicon substrates was examined by neutron reflectometry. The dPC was in the glassy state and the PMMA was in the melt state when the samples were annealed at temperatures (from 400 to 415 K) between the bulk glass transition temperature (Tg) of dPC (Tg ∼ 418 K) and PMMA (Tg ∼ 390 K). Asymmetric concentration profiles were observed as a result of composition dependence of the mobility. Once the slow moving dPC molecules leave the dPC-rich side (which was glassy) and enter the PMMA side, the dPC molecules become fast moving and diffuse freely in a viscous melt environment, while the fast moving PMMA molecules become slow as PMMA enter the glassy dPC matrix. Slight change in molecular mass of dPC gives rise to remarkable difference in concentration profile, indicating that mutual diffusion is very sensitive to molecular friction and entanglement of medium. With the penetration of PMMA into the dPC-rich side, the sluggish relaxation of dPC with high molecular mass results in the swelling of the dPC layer.
Co-reporter:Zhiyuan He, Weichao Shi, Fenghua Chen, Wei Liu, Yongri Liang, and Charles C. Han
Macromolecules 2014 Volume 47(Issue 5) pp:1741-1748
Publication Date(Web):February 27, 2014
DOI:10.1021/ma5001496
We investigated the interplay between viscoelastic phase separation (VPS) and crystallization in a dynamically asymmetric crystalline/crystalline polymer blend system of poly(butylene succinate) (PBS)/poly(ethylene oxide) (PEO). The dynamic asymmetry came from the large molecular weight difference between the slow relaxing PEO and the fast relaxing PBS molecules. The evolution of network-like structures, phase inversion, and volume shrinking processes were studied by a phase contrast microscope (PCOM). The crystallization kinetics of PBS was determined by a differential scanning calorimeter (DSC). It was found that both the crystal nucleation and growth of PBS were strongly influenced by the existence and relaxation of the entangled PEO network, even though PEO was the minor component. The nuclei of PBS were more inclined to form at the interface between phase domains due to the effect of interface-assisted crystallization. Thus, the nucleation density decreased with the decrease of interfacial area. Meanwhile, the corresponding crystal growth rate was also dependent on the VPS processes. After a second quench to a temperature below the melting point of PEO, the spatial distribution of both components and the final crystallization morphology were also significantly controlled by the initial phase structures. Compared to dynamically symmetric polymer systems, the VPS process provided more versatile pathways to control the phase and crystallization morphologies in such immiscible crystalline/crystalline polymer blends.
Co-reporter:Huan Zhang, Guangcui Yuan, Junhua Luo, and Charles C. Han
Langmuir 2014 Volume 30(Issue 37) pp:11011-11018
Publication Date(Web):2017-2-22
DOI:10.1021/la503116g
The liquid–gel–liquid transition tuned by increasing concentration of linear and hyperbranched polyethyleneimine in suspension of silica colloids, and the accompanying shear-thickening phenomena, were investigated by rheological measurements. The influence from linear and hyperbranched polymer conformation and from different size-ratio between particle and polymer on the rheological properties of suspensions flocculated by absorbing polyelectrolyte were considered. Charge neutralization and bridging mechanism are the main reasons for the flocculation of silica colloid in this study. Because of charge reversal, the irreversible bridges are turned into flexible reversible bridges with increasing adsorption amount of oppositely charged polymer, which leads to an abrupt transition from gel to liquid. Over a narrow composition range, around the gel to liquid transition region, shear-thickening flow is observed. It is found that, for given particle volume fraction, the composition region exhibiting shear-thickening for mixed suspension with linear polyethyleneimine is broader than that for mixed suspension with hyperbranched polyethyleneimine, and the onset of shear-thickening depends only on size-ratio, regardless of the actual size of particle and polymer in the range of this study. The relationship between the gel to liquid transition and shear-thickening was discussed.
Co-reporter:Zhi Zhou, Javoris V. Hollingsworth, Song Hong, He Cheng, and Charles C. Han
Langmuir 2014 Volume 30(Issue 20) pp:5739-5746
Publication Date(Web):2017-2-22
DOI:10.1021/la500866d
Rheological measurements are utilized to examine the yielding behavior of a polystyrene (PS) core and poly(N-isopropylacrylamide) (PNIPAM) shell microgel system with varying shell/core ratio. For a shell/core ratio of 0.15 at high concentrations, the suspensions show a typical hard sphere (HS) yielding response where the loss modulus (G″) exhibits a single peak due to cage breaking. As a result of tighter cages and less cage distortion prior to yielding, the peak location of G″ decreases with volume fraction. For a shell/core ratio of 1.10, which behaves like a soft jammed glass at high concentration, the suspensions exhibit a one-step yielding behavior similar to that of HS glass. However, the location of the peak in G″ increases with volume fraction, demonstrating the important role of particle deformation in the breakage of cages. For an intermediate shell/core ratio of 0.34, the system displays a two-step yielding behavior, as observed in previous reports for attractive glasses. By increasing the volume fraction, the strain of the first peak increases while the second one decreases. In addition, as the effective volume fraction increases to 112%, the two peaks merge into one broad peak. It is demonstrated that the first peak of G″ is due to deformation of the shell, and the second peak of G″ is attributed to cage breaking as a result of the cores colliding with each other. Combining these results, a yielding state diagram from typical HS to soft jammed glass is demonstrated.
Co-reporter:Yan Zhang, Fenghua Chen, Wei Liu, Songmei Zhao, Xianggui Liu, Xia Dong, Charles C. Han
Polymer 2014 Volume 55(Issue 19) pp:4983-4989
Publication Date(Web):15 September 2014
DOI:10.1016/j.polymer.2014.08.007
The correlation between rheological behavior and time evolution of the phase separation patterns was investigated in the epoxy/thermoplastic blends. Before and during the induction period of phase separation, the storage and loss modulus initially increased with epoxy curing reaction and the concentration fluctuation. At the late stage of phase separation, the modulus values also increased and showed a sharp enhancement around the epoxy gel point. However, the time evolution during the reaction induced phase separation process differed a lot at various thermoplastic (TP) concentrations. At the low TP concentrations, the rheological parameters decreased with the coarsening of sea-island structure. At the high TP concentrations, the TP-rich continuous structures initially formed and maintained until the end, resulting in a continuous increase for the rheological characters. At middle TP concentrations, formation and evolution of the three-layered structure displayed a complicated rheological behavior. It was found that the storage modulus quickly increased, reached a vertex, then rapidly decreased, reached a minimum, and increased again afterwards. Although the rheological behaviors were almost phenomenologically similar as that in the normal dynamically symmetric system, driving force for the variation was fundamentally different. Especially for the case of middle TP concentrations, the behavior of the holistic volume shrinking of the slow dynamic TP-rich network and the flowing out of the fast dynamic epoxy-rich phase from the network during this period, as radically transformed the nature of the matrix from an elastic network to a macro-phase separated layer structure and caused the dramatic change of the rheological behaviors.
Co-reporter:Wei Liu, Xia Dong, Fasheng Zou, Jian Yang, Dujin Wang, Charles C. Han
Polymer 2014 Volume 55(Issue 11) pp:2744-2750
Publication Date(Web):27 May 2014
DOI:10.1016/j.polymer.2014.04.026
The rheological properties of polybutadiene (PB)/polyisoprene (PI) in the unstable and metastable regions under oscillatory shear flow has been studied. Based on the shear quench experiment, it showed that the time dependent storage modulus G′G′ initially increased and then decreased with time in the unstable region. The concentration fluctuation led to the increasing part and the coarsening of the bicontinuous structure led to the decreasing of the storage modulus. The rheological response of the nucleation/growth in the metastable region was similar to that of spinodal decomposition. The fluctuation-assisted nucleation theory proposed by Balsara et al. was similar to the spinodal decomposition mechanism, which led to the similar rheological response. However, the continuous nucleation led to the slow growth and the almost linear decayed rheological curve, which was different from that in the unstable region. According to this theory, the relative nucleation rate on the early stage of nucleation could be calculated, which increased exponentially with the reciprocal of quench temperature in the metastable region. The spinodal point under oscillatory shear was also determined by the difference of maximum value of the storage modulus and the bulk modulus.
Co-reporter:Lina Zhang, Weichao Shi, He Cheng, Charles C. Han
Polymer 2014 Volume 55(Issue 12) pp:2890-2899
Publication Date(Web):6 June 2014
DOI:10.1016/j.polymer.2014.04.047
Although recent experiments concerning shear effects on crystallization in polymer melts are inclined to support the oriented network model, two important questions still remain open: the effect of polydispersity on shish formation and the growth mechanism of shish. In this work, a narrowdisperse poly(ethylene oxide) (PEO) is chosen as a model system to clarify the role of polydispersity for shish kebab formation after a pulse of flow. The intact structure of shish kebab observed via scanning electron microscopy (SEM), with a 150 nm wide shish core and perpendicular epitaxially grown kebabs with a long period of about 35 nm, reveals that polydispersity is not a necessary condition for shish kebab formation. On the other hand, two-step shear experiment is utilized to elucidate the growth mechanism of shish. It has been proved in a latest study that shish growth is related to the size of the growing nuclei (interval time) and second step shear rate. In this manuscript, a third factor, shear time in the second step shear, is found to be an effective factor to promote the growth of shish, which might provide a convenient processing method.
Co-reporter:Songmei Zhao, Fenghua Chen, Yingjuan Huang, Jin-Yong Dong, Charles C. Han
Polymer 2014 Volume 55(Issue 16) pp:4125-4135
Publication Date(Web):5 August 2014
DOI:10.1016/j.polymer.2014.06.027
Crystallization behaviors and kinetics of iPP in an in-situ prepared isotactic polypropylene/graphene (iPP/G) composites were studied in this paper. In samples used in this study, the graphene fillers were well dispersed, and the interfacial adhesion exhibited enhanced features between graphene and iPP components. The thermal stability of the composites was improved by about 100 °C compared to the pristine iPP. It was found that the crystallization morphology, crystallization rate and kinetics of the iPP/G composites were significantly influenced by the presence of graphene. The nucleation and epitaxial growth of iPP on the graphene surface were observed and studied in detail. It was observed that the nucleation of iPP favored to occur at the wrinkles and edges due to the good match of the lattice parameters and the weak spatial hindrance compared to the smooth surface. Numerous nuclei epitaxially formed and the size of the crystals was very small. The schematic diagram was also proposed for the nucleation and growth process of iPP on the graphene surface in the iPP/G composites. Meanwhile, the overall crystallization kinetics and crystals growth were analyzed through Avrami equation. The obtained Avrami index n decreased with the graphene loadings and was close to 2 for the iPP/G composites, which implied that the growth of iPP in the composites was in two-dimension. And this was caused by the structure of graphene and the spatial confinement effect of graphene platelets in the iPP/G composites.
Co-reporter:Jingjing Yang, Yongri Liang, and Charles C. Han
Langmuir 2014 Volume 30(Issue 1) pp:394-401
Publication Date(Web):2017-2-22
DOI:10.1021/la4041387
In this work, we used poly(l-lactide)-block-poly(ethylene glycol) (PLLA-b-PEG) copolymer thick films to investigate the effect of crystallization on surface segregation, surface crystal orientation, and morphology by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), reflection optical microscopy (ROM), and two-dimensional grazing incident wide-angle X-ray scattering (2D GIWAXS) methods. ATR-FTIR results indicated that the surface fraction of PLLA block increased from 0.48 to 0.79 when Tc,PLLA increased from 70 to 110 °C. Polarized ATR-FTIR and 2D GIWAXS results indicated that PLLA crystal lamellae preferentially oriented parallel to the film surface with increasing Tc,PLLA. The surface crystallinity of PLLA was almost independent of Tc,PLLA, while the surface crystallinity of PEG decreased with increasing Tc,PLLA. On the basis of surface crystal orientation and crystallization kinetics, we suggested that the excess of PLLA component at the surface was mainly dominated by a coupling effect of crystallization behavior and surface segregation.
Co-reporter:Li-na Zhang;Wei-chao Shi 韩志超
Chinese Journal of Polymer Science 2014 Volume 32( Issue 9) pp:1260-1270
Publication Date(Web):2014 September
DOI:10.1007/s10118-014-1500-3
A uniform to accelerated crystal twisting transition is observed in deuterate polyethylene/poly(ethylene-altpropylene) (d-PE/PEP) blend films. And the band period is a function of initial d-PE concentration, quench depth and annealing time of phase separation. As Keith and Padden suggested, twisting of lamella is due to the unbalanced stress on its both sides, which can supply a satisfying explanation to banded spherulites formed in homogeneous systems. When it comes to d-PE/PEP blend system, in homogeneous 99% d-PE/PEP (weight fraction of d-PE) blend film, the formation of banded spherulite is observed as a result of uniform twisting of ribbon like d-PE lamellae along the radial direction. With the amorphous PEP piling up, it transfers into accelerated edge-on to flat-on twisting due to crystallization assisted phase separation. The mechanism can be interpreted as following: d-PE molecules must inter-diffuse to the twisting growth front to continue the secondary nucleation and growth process. Meanwhile, the amorphous PEP molecules are rejected and accumulated at the twisting growth front. Once the d-PE lamella begins to twist because of unbalanced stress on both sides, the accumulated rubber phase at the growth front strengthens the unbalance and accelerates the edge-on to flat-on twisting. The concentration wave propagates further away with constant speed, and leads to concentric ring pattern with periodic nonuniform twisting along the radial direction. Since this is a kinetic effect, the band period can be controlled through initial d-PE concentration, quench depth and annealing time of phase separation. Our result shows that crystallization assisted phase separation can modify lamella growth kinetic pathway, thereby assisting concentric ring pattern formation.
Co-reporter:Fa-sheng Zou;Xia Dong 董侠;Wei Liu;Du-jin Wang
Chinese Journal of Polymer Science 2014 Volume 32( Issue 6) pp:718-730
Publication Date(Web):2014 June
DOI:10.1007/s10118-014-1443-8
The morphology evolution and the corresponding linear viscoelastic behavior of the phase-separating polybutadiene (PB)/low vinyl content polyisoprene (LPI) blend have been investigated by phase contrast optical microscopy (PCOM), small-angle light scattering (SALS) and rheometry. Two kinds of structure evolutions and rheological responses have been observed. It is found that the co-continuous structure generally gives a power law behavior of the dynamic storage modulus versus frequency and the coarsening of co-continuous structure leads to a decrease of the storage modulus. For the droplet-matrix structure, a platform modulus is observed at the mediate frequencies, followed by the typical terminal relaxation behavior of storage modulus at the extremely low frequencies. The decreasing platform modulus and increasing terminal modulus with the growth of droplets are observed and can be well interpreted by the simplified Palierne model. The platform modulus and terminal modulus at a given frequency are found to be scalable with the phase separation time. Besides, the characteristic relaxation time and domain size of the droplets have been obtained by rheology. And it seems that the rheologically determined droplet dimensions are consistent with the ones determined by PCOM and SALS.
Co-reporter:Heran Wang, Ming Cheng, Jianming Hu, Chenhong Wang, Shanshan Xu, and Charles C. Han
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 21) pp:11014
Publication Date(Web):October 11, 2013
DOI:10.1021/am403250t
A strategy of using silver nanoparticle (AgNP)-loaded electrospun membrane as a novel coating material for preventing implant associated infections is reported. The strategy takes both the advantages of the excellent antibacterial as well as no drug resistance properties of AgNPs, and the widely used biodegradable electrospun membrane to serve as AgNP carrier and physical obstruction of bacteria adhesion. However, AgNPs have not been applied in clinical treatment yet because the concern of the potential toxicity. For the first time, we systematically investigated toxicity of AgNP-based coating materials in vitro and in vivo. Three dosages (0.1, 0.5, and 1.0 wt %) of silver nanoparticles (AgNPs) were embedded in biodegradable PLGA electrospun membranes as treatment devices to determine the precise concentration of AgNPs, minimize the dosage, and consequently reduced the toxicity in clinical applications. On the basis of antibacterial results and toxicity evaluations, PLGA electrospun membranes containing 0.5 wt % of AgNPs was considered as the most suitable combination, which is safe and effective for clinical application.Keywords: antibacterial activity; biotoxicity; implant associated infections; implant coating material; PLGA electrospun nanofibers; silver nanoparticles;
Co-reporter:Zhiguo Zhao, Jianfen Zheng, Bo Peng, Zhiyong Li, Haiyuan Zhang, Charles C. Han
Journal of Membrane Science 2013 Volume 439() pp:12-19
Publication Date(Web):15 July 2013
DOI:10.1016/j.memsci.2013.03.036
•Dilute PVDF solution was investigated in Loeb–Sourirajan process.•A type of screen microporous membrane with novel structure was obtained.•A composite screen microfiltration membrane (SMM) was constructed and evaluated.•The SMM possesses excellent filtration performance and anti-fouling property.A dilute PVDF solution with concentration lower than 8 wt% was investigated using the Loeb–Sourirajan process to produce an asymmetric microporous membrane. The parameters such as polymer concentration and solution composition were optimized and a type of asymmetric microporous membrane with high porosity, thin barrier layer, narrow pore size distribution, short pore flow distance and self-similar structure was obtained. A composite microfiltration membrane, consisting of an asymmetric microporous membrane, ultrathin nanofibers and non-woven PET fabric was constructed and evaluated in the filtration test. In comparison to the commercial microfiltration membrane and raw electrospun nanofibrous membrane, the novel composite microfiltration membrane exhibited a much better performance: dramatically high water flux, high selectivity, low fouling tendency and excellent flux recovery property.Graphical abstract
Co-reporter:Guangmin Wei, Chuanzhuang Zhao, Javoris Hollingsworth, Zhi Zhou, Fan Jin, Zexin Zhang, He Cheng and Charles C. Han
Soft Matter 2013 vol. 9(Issue 41) pp:9924-9930
Publication Date(Web):02 Sep 2013
DOI:10.1039/C3SM51927A
The mechanism of two-dimensional (2D) crystal formation from an air-drying suspension of soft microgel particles is investigated via in situ confocal laser scanning microscopy (CLSM). According to the time-resolved radial distribution function g(r), the process can be divided into two separate stages, i.e., nucleation and growth. During the air-drying process, the soft poly(N-isopropylacrylamide-co-methacrylic acid) (P(NIPAM-co-MAA)) spherical microgel particles first deform into a disk-like shape as the thickness of the concave water layer becomes comparable to their diameter. Subsequently, the particles are driven together by attractive capillary forces to initiate the nucleation process. Once the critical nuclei size is reached, the 2D nuclei can then grow into a crystal. Subsequently, during the crystal growth process, convective water flow compels free microgel particles from the liquid phase to the crystal growth front. While trapped in the growth front, the particles rearrange themselves into crystal structures. The size of 2D crystals increases quadratically with time. Ideally, these findings will promote more experimental and theoretical work aimed at elucidating the 2D fluid-to-solid transition of soft microgel particles, as well as 2D soft disk crystal growth in condensed matter physics.
Co-reporter:Huarong Nie, Aihua He and Charles C. Han
RSC Advances 2013 vol. 3(Issue 30) pp:12398-12402
Publication Date(Web):07 May 2013
DOI:10.1039/C3RA22835E
In this work, electrospun poly(lactide-co-glycolide) (PLGA) fibrous membranes were functionalized with radionuclides by surface modification. After the introduction of chitosan and bifunctional ligands (DTPA) on soft hydrolyzed PLGA nanofibrous membranes, more than 80% of the radionuclides (90Y) in aqueous solutions were attached as labels to the target nanofibers. To get a high chelating efficiency without changing the physical properties of the membranes, the hydrolysis conditions, the reactive media for the introduction of DTPA, and the chelating time were thoroughly investigated. These radionuclide labelled PLGA fibrous membranes have similar mechanical properties as human tissues. 90Y on PLGA nanofibers shows a desirable stability of more than four half-lives.
Co-reporter:Jihui Wang
Journal of Applied Polymer Science 2013 Volume 129( Issue 5) pp:2977-2985
Publication Date(Web):
DOI:10.1002/app.39030
Abstract
Relationship between phase separation and crystallization of polypropylene/poly(propylene-1-octene) in-reactor alloy (iPP/PPOc) were studied using optical microscopy, scanning electron microscopy, and differential scanning calorimetry. Optical microscopy was used to monitor nuclei density and spherulite growth rates, providing complementary information about the effect of liquid–liquid phase separation (LLPS) on crystallization behavior. We found that LLPS process had a retardation effect on crystallization rate and had a dominant effect on the final crystalline morphology of the iPP/PPOc alloy. By simply changing the LLPS time or temperature, we could control the size and the distribution of the elastomer phase that dispersed in the iPP spherulites. The growth rate of the spherulites significantly depended on the degree of LLPS. Higher degree of phase separation reduced nuclei density and the growth rate of spherulites. However, it was helpful to the formation of more perfect spherulites. But surprisingly, there seemed to be little variation of crystallinity between the two quenching procedures (i.e., single quench vs. double quench). Overall, the competition between LLPS and crystallization significantly influenced the structural and morphological development of the iPP/PPOc alloy. By controlling the interplay between LLPS and crystallization of iPP/PPOc alloy, it was possible to control the structure and morphology as needed in applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
Co-reporter:Bo Shen, Yongri Liang, Julia A. Kornfield, and Charles C. Han
Macromolecules 2013 Volume 46(Issue 4) pp:1528-1542
Publication Date(Web):February 11, 2013
DOI:10.1021/ma3023958
Isotactic polypropylene has been systematically studied with in situ optical microscopy to obtain a real space view of the morphology evolution of shear induced crystallization as a function of shear rates and shear time to elucidate the mechanism of shish formation. The critical shear time for inception of shish formation on the shear rate have provided an important understanding of the molecular and entangled network relaxation in relation to the shish formation. Also the observation of a typical shear time dependent comet like shish-kebab structure formation on the interface and the morphological growth of the shish from a fiber inside our sample have led to a new hypothesis that the shish is formed through a multiple discrete steps instead of forming directly to the final most stable state, this means that a transition state may be existed before shish growth. Two steps shear experiments with various time intervals between each step were designed to verify our proposed transition state mechanism, which can be observed much directly and obviously through real-space morphology, especially at low shear rate with long shear time. Another time dependent relaxation time is introduced base on shear rate dependent experiment after the first step shear and has close relationship with the existence of the critical shear time. A general framework for the shish formation has been established which can capture all the observed morphological features well, including the existence of the critical shear time at a given shear rate.
Co-reporter:Huan Zhang, Guangcui Yuan, Chuanzhuang Zhao, and Charles C. Han
Langmuir 2013 Volume 29(Issue 39) pp:12110-12117
Publication Date(Web):2017-2-22
DOI:10.1021/la402577q
The rheological property of mixed suspensions of silica colloid and hyperbranched polyethyleneimine (hPEI) was studied as functions of particle volume fraction, ratio of polymer to particle, and pH value. A mechanism of liquid–gel–liquid transition for this mixed system was proposed based on the amount and the conformation of polyelectrolyte bridges which were able to self-arrange with solution environments. The hPEI, which is adsorptive to the surface of silica colloid, can induce bridging or stabilizing effect between particles depending on whether the concentration of hPEI (Cp) is smaller or larger than the equilibrium adsorbed amount (Cp*) for a given volume fraction of particles. In dilute colloid suspensions, the Cp* can be determined by dynamic light scattering as the correlation function returns back to a narrow distributing single relaxation with increasing Cp. In concentrated colloid suspensions, the Cp* can be determined by rheological measurement as gel–liquid transition occurs with increasing Cp. The Cp* is an important concentration ratio of polymer to particle denoting the transition of irreversible and reversible bridging. For mixed suspensions at equilibrium adsorbed state (Cp ≈ Cp*), the adsorption–desorption of polymer bridges on the particles can reversibly take place, and shear thickening is observed under a steady shear flow as a result of rapid extension of bridges when the relaxation time scale of extension is shorter than that of desorption.
Co-reporter:Jian Yang, Xia Dong, Weichao Shi, Fasheng Zou, Wei Liu, Dujin Wang, Charles C. Han
Polymer 2013 Volume 54(Issue 11) pp:2606-2610
Publication Date(Web):9 May 2013
DOI:10.1016/j.polymer.2013.03.047
The growth of transcrystallites induced by fracture stress was studied in the solution casted polystyrene (PS)/poly(ethylene oxide) (PEO) blends films. Both the structure geometry of the crack edge and the effect of local fracture stress on the crystallization were considered. It was found that the local fracture stress contribution is the most important factor to the formation of transcrystallites. Transcrystallites were obtained when PEO crystallized before the local fracture stress was relaxed, while only regular spherulites were obtained when crystallization took place after the relaxation of the local fracture stress.
Co-reporter:Zhiyuan He, Yongri Liang, Pingli Wang, Charles C. Han
Polymer 2013 Volume 54(Issue 9) pp:2355-2363
Publication Date(Web):19 April 2013
DOI:10.1016/j.polymer.2013.02.020
The crystalline/crystalline polymer blend of poly(butylenes succinate)/poly(ethylene oxide) (PBS/PEO) exhibited lower critical solution temperature (LCST) phase separation behavior at temperatures above the melting point of PBS, which was measured by phase contrast optical microscopy (PCOM) technique. In this work, we determined the LCST phase diagram of PBS/PEO blends, and then investigated the effect of liquid–liquid phase separation (LLPS) on the crystallization kinetics and morphologies of PBS/PEO (40/60 wt/wt) blend. Based on polarized optical microscopy (POM), scanning electron microscopy (SEM) and differential scanning calorimeter (DSC) results, we found that the spherulite morphology and crystallization kinetics of PBS were strongly influenced by the initial LLPS structure; because the kinetics of liquid–liquid phase dissolution was much slower than that of crystallization. The effect of LLPS on the primary nucleation density and crystal growth rate of PBS were strongly dependent on the crystallization temperature of PBS. After a second quench to a temperature below the melting point of PEO, the fractionated crystallization of PEO was observed. The competition between the kinetics of LLPS and the driving force of PBS crystallization controlled the spatial distribution of PEO in PBS spherulites, thus essentially determined the confined conditions of the PEO crystallization. The results indicated that the LLPS was an effective process to control the crystallization kinetics and morphology in crystalline/crystalline polymer blend systems.
Co-reporter:Songmei Zhao, Fenghua Chen, Chuanzhuang Zhao, Yingjuan Huang, Jin-Yong Dong, Charles C. Han
Polymer 2013 Volume 54(Issue 14) pp:3680-3690
Publication Date(Web):21 June 2013
DOI:10.1016/j.polymer.2013.04.059
Morphological structure development of the in-situ polymerized isotactic polypropylene/graphene nanocomposites was investigated during the annealing process. The material was prepared via an in-situ slurry polymerization method with graphene-supported Ziegler–Natta catalyst. An interpenetrating network was observed at a relatively low graphene concentration after the sample was annealed for a long period (one to several hours). Alternative Conductivity impedance spectroscopic measurements showed a remarkable electrical conductivity increase of several orders of magnitude after the network was formed. At very low graphene content, although macroscopic network cannot be formed, the electrical conductivity can be enhanced through annealing as well. It implied that the rearrangement of the clusters or aggregates was necessary and such rearrangement favored the network formation. The network forming process was investigated through optical and electron microscopy methods and discussed based on the viscoelastic phase separation model. The effect of network on the crystallization behaviors was also investigated. It showed that the overall crystallization was improved by the presence of graphene platelets, but depressed after the network was formed, which was due to the spatial confinement and the decrease of total surface area available for heterogeneous nucleation.
Co-reporter:Jing Jin, Hongyu Chen, M. Muthukumar, Charles C. Han
Polymer 2013 Volume 54(Issue 15) pp:4010-4016
Publication Date(Web):8 July 2013
DOI:10.1016/j.polymer.2013.05.050
Mesophase separation between the incompatible blocks in multiblock copolymers OBC (Olefin Block Copolymers), coupled with the macrophase separation in its blends with iPP (isotactic polypropylene), makes iPP/OBC a unique blend system to understand the interaction between multiple phase separations and the subsequent or simultaneous crystallization in multi-scales. The role played by OBC content as well as its molecular structure on phase morphology and crystallization kinetics in blends of iPP/OBC has been investigated systematically to demonstrate synergistic coupling between thermodynamics and kinetics. The total isothermal crystallization rate, nucleation density (the nuclei number per unit volume) and linear growth rate of iPP are found to be composition and component dependent, which can be attributed to the interplay among the enhanced mobility due to the presence of a more mobile component (lower glass transition temperature and lower melting temperature) serving as an “accelerant”, the associated composition dependent inter-diffusion coefficient, and the obstruction effect caused by the OBC aggregates with increasing the diluent concentration. Furthermore, the distinct phase separation morphology determined by the compatibility between iPP and various OBC influenced the growth rate of iPP spherulite as well.
Co-reporter:Jingjing Yang, Yongri Liang, Weichao Shi, Han Sup Lee, Charles C. Han
Polymer 2013 Volume 54(Issue 15) pp:3974-3981
Publication Date(Web):8 July 2013
DOI:10.1016/j.polymer.2013.05.032
Co-reporter:Zhiyuan He, Yongri Liang, and Charles C. Han
Macromolecules 2013 Volume 46(Issue 20) pp:8264-8274
Publication Date(Web):October 3, 2013
DOI:10.1021/ma4015214
The confined and fractional crystallization behavior of poly(ethylene oxide)(PEO) in miscible poly(butylene succinate)(PBS)/PEO blends has been investigated. Both nucleation and growth of PEO crystals through the two-step crystallization process were significantly influenced by the morphology of pre-existed PBS spherulites. At the first crystallization step, the PEO component as diluents was segregated into different regions (interlamellar, interfibrillar and interspherulitic) of PBS crystals, which was dependent on the crystal growth rate of PBS and the diffusion coefficient of PEO. With the increase of crystallization temperatures of PBS (Tc,PBS), more and more PEO molecules were excluded out of the lamella stacks of PBS, and the segregations of PEO became larger and larger. Meantime, the connectivity between the adjacent PEO domains was reduced dramatically. At the second crystallization step, PEO crystallized subsequently within the existed frameworks of PBS spherulites formed at various Tc,PBS. On the one hand, the nucleation rate of PEO was determined by the total solid–liquid interfacial area between PBS crystals and PEO domains, which could significantly reduce the free energy barrier of nucleation embryos. As Tc,PBS increased, the nucleation rate of PEO decreased with the decrease of PBS crystal surfaces which were around PEO domains. The fractional crystallization of PEO occurred when the nuclei formed at various supercoolings. On the other hand, the crystal growth rate of PEO was mostly influenced by the connectedness between the PEO domains. With the increase of Tc,PBS, the continuous phases of PEO were transformed into isolated domains. The crystal growth of PEO decreased gradually, due to the restrictions to the diffusion of PEO chains. PEO could only nucleate and grow inside each isolated domains, just forming tiny PEO crystals. It was found that the crystallization of PEO was dependent not only on the diffusion length of PEO, but also on the intrinsic morphological features of PBS spherulites.
Co-reporter:Weichao Shi, Jingjing Yang, Wei Liu, Lina Zhang, and Charles C. Han
Macromolecules 2013 Volume 46(Issue 6) pp:2516-2520
Publication Date(Web):March 15, 2013
DOI:10.1021/ma400032w
Co-reporter:Heran Wang, Min Li, Jianming Hu, Chenhong Wang, Shanshan Xu, and Charles C Han
Biomacromolecules 2013 Volume 14(Issue 4) pp:
Publication Date(Web):February 28, 2013
DOI:10.1021/bm301997e
A multiple targeted drug carrying bilayer membrane for preventing an abdominal adhesion is prepared by electrospinning. Two bioactive drugs were successfully incorporated into this bilayer membrane and can be independently released from nanofibrous scaffolds without losing structural integrity and functionality of the anti-adhesion membrane. Besides, the drug release profile could be easily adjusted by optimizing the swelling behavior of the fibrous scaffold. The inner layer of the bilayered fibrous membranes loaded with carbazochrome sodium sulfonate (CA) showed an excellent vascular hemostatic efficacy and formed little clot during in vivo experiment. The outer layer loaded with tinidazole (TI) had outstanding antibacterial effect against the anaerobe. We believe this approach could serve as a model technique to guide the design of implants with drug delivery functions.
Co-reporter:Mingji Wang, Guangcui Yuan, Charles C. Han
Polymer 2013 Volume 54(Issue 14) pp:3612-3619
Publication Date(Web):21 June 2013
DOI:10.1016/j.polymer.2013.05.016
Bisphenol-A polycarbonate (PC) and amorphous polyamide (aPA) were used as reactive system to study the interfacial interchange reaction between condensation polymers. Aminolysis is the main process during thermal annealing at 160–180 °C. The simultaneously scission of PC chains and formation of PC-aPA copolymer chains during the reaction process, can act as interfacial compatibilization agents between incompatible homopolymers. Reaction kinetics measured by in-situ Fourier transform infrared spectrum (FTIR) at interfaces of well-separated bilayer films and phase separation blends were compared. The reaction follows a first-order diffusion controlled mechanism and three time regimes were observed. First, the functionalized chains located in the vicinity of the interface participate into the reaction and the annealing time dependence of the integral area of difference IR spectra follows a power law relationship as [Area] ∼ t1/4. Second, a depletion layer of reactants in the interfacial region is formed with the progression of reaction, and center-of-mass diffusion of reactants is required for further reaction which results in a transition of the power law relationship into [Area] ∼ t1/2. Finally, the potential barrier arising from the previously formed copolymers at the interface suppressed the reaction. When the conversion reaches a critical value, thermal fluctuation can induce interface destabilization. An acceleration of reaction rate observed by FTIR for sample annealed at 180 °C is synchronous with the interfacial roughness development analyzed by atomic force microscopy.
Co-reporter:Haiyuan Zhang, Jianfen Zheng, Zhiguo Zhao, Charles C. Han
Journal of Membrane Science 2013 442() pp: 124-130
Publication Date(Web):
DOI:10.1016/j.memsci.2013.04.032
Co-reporter:Guangmin Wei, Dongdong Yao, Zhiyong Li, Ye Huang, He Cheng, and Charles C. Han
Macromolecules 2013 Volume 46(Issue 3) pp:1212-1220
Publication Date(Web):January 14, 2013
DOI:10.1021/ma3020504
The mechanism of charge-transfer complexation in electron-donor (D)/electron-acceptor (A) active layer was studied for a pseudobinary blend model system, poly(4-vinylpyridine) (P4VP)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in DMF solution, by a combination of light scattering (LS), transmission electron microscopy (TEM), and UV–vis spectroscopy. The time evolution of the system can be characterized by four distinct stages, i.e., induction, complexation, aggregation, and precipitation. In the induction stage, a combined dynamic LS and static LS studies showed that the conformation of P4VP remained unchanged, while the UV–vis indicated that the charge-transfer complexation had almost accomplished with an obvious broadening at C60 characteristic absorption peak of 330 nm. In the complexation stage, each P4VP chain complexed with about three PCBM molecules at cP4VP = 4.1 × 10–2 g/mL, cPCBM = 5.8 × 10–4 g/mL, and the molar ratio [4VP]/[PCBM] = 57:1 and shrinked in size with almost no change in the UV–vis spectrum. In the subsequent aggregation stage, P4VP/PCBM complexes aggregated with each other to form spherical aggregates with again unchanged UV–vis signals. The free association model (FA model) can be used to explain this mechanism. In the final precipitation stage, huge P4VP/PCBM agglomerate began to phase out with a clear decrease of the scattered light intensity in the LS. The almost unchanged UV–vis spectrum after the induction stage proved that the electronic transition from ground to excited state is not necessarily to be influenced by any inter- or intrapolymer structural transition. Our kinetics study on the mechanism of the complexation/association/aggregation shed some light on the possible morphology control in the D/A active layer.
Co-reporter:Weichao Shi, Fenghua Chen, Yan Zhang, and Charles C. Han
ACS Macro Letters 2012 Volume 1(Issue 8) pp:1086
Publication Date(Web):August 13, 2012
DOI:10.1021/mz300312e
Polymer blends with dynamic asymmetry have attracted much interest recently. In this study, we report a more typical case where the dynamically asymmetric system is highly immiscible. We find that there is a transient network growth and phase inversion for the slow minor component. The network structure shows a hierarchical growth behavior, which is the result of competition between a slow relaxation-controlled concentration growth on local scale and a fast hydrodynamic growth on large scale. When phase separation couples with a subsequent crystallization, the interfacial boundary may assist lateral crystallization and irregular spherulites would grow epitaxially around the amorphous component-rich domains. The interface may play the role of substrates for heterogeneous nucleation. These phenomena may help us with morphological control in material processing.
Co-reporter:Zhiguo Zhao, Jianfen Zheng, Mingji Wang, Haiyuan Zhang, Charles C. Han
Journal of Membrane Science 2012 Volumes 394–395() pp:209-217
Publication Date(Web):15 March 2012
DOI:10.1016/j.memsci.2011.12.043
Liquids filtration technology as one of the paths to sustainable water use is getting more and more attention. A new type of high flux ultrafiltration (UF) or nanofiltration medium based on electrospun fibrous scaffold and ultrathin top barrier layer was fabricated recently. Based on this new method, the chitosan (CTS) which is one of the best top layer materials due to its hydrophilicity and high water-permeability was coupled with electrospun polyvinylidene fluoride (PVDF) nanofibers to compose a new type UF membrane. In this work, the chitosan was crosslinked and modified by glutaraldehyde (GA) and terephthaloyl chloride (TPC) to adjust its water resistance and surface properties. The modified membrane was characterized by FTIR, SEM, UV-spectra, static water contact angle analysis and filtration test. The modified membrane gets broader operating environment range and keeps a good flux rate and rejection efficiency in bovine serum albumin (BSA) filtration tests at 0.2 MPa, about 70.5 L/m2 h, rejection efficiency >98% which are higher than that of 57.1 L/m2 h, rejection efficiency∼98% of the commercial UF membranes, while the fouling of the membrane was kept at a very low level. This work may provide a practical possibility to the water filtration industry.Graphical abstractHighlights► Electrospinning based composite ultrafiltration membrane was fabricated. ► Top chitosan layer was co-modified with both dialdehyde and acyl chloride. ► Acid resistance and anti-fouling properties were introduced. ► The water flux rate and the BSA rejection efficiency were excellent.
Co-reporter:Chuanzhuang Zhao, Guangcui Yuan, Di Jia and Charles. C. Han
Soft Matter 2012 vol. 8(Issue 26) pp:7036-7043
Publication Date(Web):31 May 2012
DOI:10.1039/C2SM25409C
In this work, aggregation and gelation behaviour of mixed suspensions of polystyrene microspheres and poly(N-isopropylacrylamide) microgels were studied. In dilute microsphere suspensions, with increasing concentration of microgel (ϕMG), microspheres first aggregated with each other through the bridging of the microgels, then dispersed individually when saturated adsorption was achieved, and finally depletion clusters formed at even higher concentrations of microgel. The concentration of microgel for saturated adsorption (ϕ*MG) is in a linear relationship with the given concentration of microsphere (ϕMS). For given ϕMS, the largest bridging clusters formed at ϕMG ≅ 0.5 ϕ*MG. In concentrated microsphere suspensions, with increasing ϕMG, the mixed suspensions showed a liquid–“bridging gel”–liquid–“depletion gel” transition. The maximum modulus and yielding stress of the bridging gel are also obtained at ϕMG ≅ 0.5 ϕ*MG. The gelation of the microsphere can be explained by the percolation of the clusters and the elasticity of bridging gel arising from the mutual attractions between the microspheres.
Co-reporter:Weichao Shi, Xu-Ming Xie, and Charles C. Han
Macromolecules 2012 Volume 45(Issue 20) pp:8336-8346
Publication Date(Web):October 11, 2012
DOI:10.1021/ma301592a
The interplay between crystallization and phase separation has been intensively studied recently. In this study, we extended the research into a dynamically asymmetric blend composed of amorphous poly(methyl methacrylate) (PMMA) and crystalline poly(ethylene oxide) (PEO). The large dynamic asymmetry induces network stress in concentration growth. We find that crystallization is seriously frustrated when it couples with a simultaneous viscoelastic phase separation. In a single quench experiment, normal spherulites grew in a limited temperature range when crystallization was faster, while crystallization was frustrated at deep quenches when phase separation was faster. In a double quench experiment, crystallization was more difficult to occur after the prior phase separation at a higher temperature. The calorimetric results indicated that both melting temperatures and enthalpies of crystallization decreased in the coupled viscoelastic phase separation. We propose that it is the network stress in the concentration growth that leads to the frustration of crystallization.
Co-reporter:Weichao Shi and Charles C. Han
Macromolecules 2012 Volume 45(Issue 1) pp:336-346
Publication Date(Web):December 1, 2011
DOI:10.1021/ma201940m
We investigated the dynamic competition between crystallization and phase separation in a dynamically asymmetric blend of poly(methyl methacrylate) (PMMA) and poly(ethylene oxide) (PEO). Because of a large difference in glass transition temperatures between these two components, the phase transition dynamics is slowed down and can be observed in more detail. There is a morphological inversion from spherulitic to concentric ring patterns by adjusting the quench depth. Under deep quench, phase separation tends to be enhanced by the large concentration deviation at the growth interface of crystals, and propagates outward with convective concentration waves. Meanwhile, short needle-like crystals appear in the phase separated domains, compared with long crystal strips in a spherulitic pattern. A general dynamic competition model is proposed to qualitatively interpret the complex interplay between crystallization and phase separation. On the basis of this model, various morphologies are observed and predicted.
Co-reporter:Weichao Shi, Jian Yang, Yan Zhang, Jun Luo, Yongri Liang, and Charles C. Han
Macromolecules 2012 Volume 45(Issue 2) pp:941-950
Publication Date(Web):January 5, 2012
DOI:10.1021/ma202046c
Crystallization dynamics and lamellar orientation are affected under the dynamic interplay between crystallization and phase separation. We carried out the experiment in a dynamically asymmetric blend of amorphous poly(methyl methacrylate) (PMMA) and crystalline poly(ethylene oxide) (PEO). If phase separation is really weak, lamellae are normally grown in the radial direction within spherulites. Growth rate shows a bell-like curve with respect to temperature. However, when strong phase separation intervenes, the growth rate curve is characterized by double peaks, one of which is dominated by crystallization and the other by phase separation. Meanwhile, lamellae tend to orient in the tangential direction in concentric alternating structures, whose formation mechanism has been explained in previous studies. This lamellar orientation inversion is reflected by a negative to positive birefringence inversion under optical microscopy. Within lamellar stacks, more amorphous molecules tend to be pushed out under the effect of phase separation, leading to smaller long period.
Co-reporter:Tongchen Sun, Xia Dong, Fenghua Chen, Yong Zhou, Jun Luo, Dujin Wang, Charles C. Han
Polymer 2012 Volume 53(Issue 5) pp:1054-1057
Publication Date(Web):28 February 2012
DOI:10.1016/j.polymer.2012.01.023
Isotactic polypropylene (iPP)/organo-montmorillonite (OMMT) nanocomposite was modified by poly(ethylene-co-octene) (PEOc). PEOc-rich domains were well dispersed in the iPP matrix, with narrowly distributed size. OMMT layers were well dispersed, mainly intercalated and partially exfoliated. Compared with the case in the binary composites, many OMMT layers were preferential distributed inside and around the PEOc-rich domains in the ternary composite samples, which formed an enhanced OMMT filler network. The reason for the OMMT preferential distribution was considered to be dragged or wrapped by PEOc-rich domains during sample preparation and phase separation.
Co-reporter:Jihui Wang, Hui Niu, Jinyong Dong, Jiang Du, Charles C. Han
Polymer 2012 Volume 53(Issue 7) pp:1507-1516
Publication Date(Web):22 March 2012
DOI:10.1016/j.polymer.2012.02.017
A series of isotactic polypropylene/poly(propylene-1-octene) (iPP/PPOc) in-reactor alloys were synthesized by a one-step polymerization process, using Metallocene/Ziegler–Natta hybrid catalyst. The alloys were characterized by FT-IR, DSC, optical microscopy and SEM. The results suggested that the spherical morphology was maintained during one-step polymerization process, which provided a potential application for one-step polyolefin in-reactor alloys. A characteristic “shell–core” structure of the nascent alloy particles was observed for the first time. This phenomenon may be due to the difference between the homopolymerization and copolymerization rate at different active centers. It was also found that the majority of the elastomers in the matrix were homogeneously distributed in the alloys. The introduction of the relatively long 1-octene branches could effectively reduce the crystal size and the crystallinity of the obtained iPP/PPOc alloys and made it possible to vary their rigidity and elasticity in a wide range. The crystallization kinetics of the alloys with pure iPP was also investigated. With the increase of elastomer content, an increase of nucleation density (the nuclei number per unit area) and the decrease of crystal perfection could be clearly observed. In comparison with pure PP, the overall crystallization rates and the growth rates of the spherulites of the alloys decreased obviously. These results indicated that the growth rate of the spherulites was the decisive step for the overall crystallization rate in this case, which can be explained on the basis of dilution effect and obstruction effect on the mobility of PP chains in the propylene–octene copolymer. Investigation of the mechanical properties indicated that notched Izod impact strength of iPP/PPOc alloys have obviously increased in comparison with that of pure iPP. The improvement of impact strength can be mainly attributed to the increase of random copolymer content. Based on the understanding of microstructure and phase morphology, the correlation between morphological structure and mechanical properties has been established.
Co-reporter:Junyu Li, Wei Li, He Cheng, Lina Zhang, Yang Li, Charles C. Han
Polymer 2012 Volume 53(Issue 12) pp:2315-2319
Publication Date(Web):25 May 2012
DOI:10.1016/j.polymer.2012.03.054
Time-resolved synchrotron small angle X-ray scattering (SAXS) was used to investigate the early stages of crystallization in melt crystallized polyethylene. Classic Gibbs nucleation or density fluctuation theory can be used to describe the primary nucleation mechanism. At 110 °C, no signal of crystallization can be detected by SAXS for 30 min. When it is lower than 110 °C, the low q scattering intensity (0.008 < q < 0.03 Å−1) begins to upturn, and the primary nucleation process starts. The measured fractal dimension of the critical nuclei is in the vicinity of 3 which is close to the prediction of classic Gibbs nucleation theory. The growth rate of density fluctuations R(q) at different scattering vector q for different temperatures was obtained by analyzing the increase of scattering intensities. The results show that the growth rate of density fluctuation gets much bigger with the decrease of the isothermal crystallization temperature, but there is no signal of spinodal decomposition mechanism, in which there should be a linear relationship between R(q)/q2 and q2.Graphical abstract
Co-reporter:Jianfen Zheng, Haiyuan Zhang, Zhiguo Zhao, Charles C. Han
Polymer 2012 Volume 53(Issue 2) pp:546-554
Publication Date(Web):24 January 2012
DOI:10.1016/j.polymer.2011.12.018
To expand the application of electrospun fibers or electrosprayed beads, micro-nano hierarchical structures of polystyrene (PS) have been constructed through the adjustment of solvent, polymer concentration, environment humidity, electrospinning temperature, etc. Primary structures, such as fibers, beads and bead-on-string structure, as well as secondary structures, such as nanopores, nanopapilla and net-work structure, have been constructed. Solvent plays an important role in the construction of both primary structures and secondary structures. By using N,N-dimethylformamide (DMF), tetrahydrofuran (THF) and mixed solvent of DMF/THF, the micro-nano hierarchical structures can be controlled. Humidity is a key factor to the construction of secondary structures. The obtained fibers or beads have smooth surface at low humidity. While at high humidity, secondary structures tend to appear. For the PS/DMF system, vapor-induced phase separation may be the most pertinent mechanism to explain the formation of secondary structures. While for the PS/THF system, breath figure theory can explain the formation of uniform nanopores properly.
Co-reporter:Fasheng Zou, Xia Dong, Demiao Lin, Wei Liu, Dujin Wang, Charles C. Han
Polymer 2012 Volume 53(Issue 21) pp:4818-4826
Publication Date(Web):28 September 2012
DOI:10.1016/j.polymer.2012.08.052
The morphological and rheological responses to the transient and steady shear flow for a phase-separated polybutadiene (PB)/low vinyl content polyisoprene (LPI) blend have been investigated. Under steady shear flow where the applied shear rate is not too large, the steady sheared structures become increasingly anisotropic and interconnected with an “en route” to the formation of string phases as shear rate increases. After that, the further increase of shear rate leads to a blurred domain interface. These shear-induced complex structures in turn affect the rheological response greatly and both the shear thinning and shear thickening were observed in the steady shear behavior of the phase-separated PB/LPI blend. Under transient shear flow, the time (or strain) dependence of viscosity and morphology after a shear rate jump were extensively studied in order to obtain the insight into the steady state formation and found to be mainly determined by the final shear rates. Depending on whether the transient string phases which were formed by the transient shear flow can be stabilized and with clear domain interface, three kinds of transient shear viscosity changes have been observed. Some of the observations are quite different from the model immiscible blend and believed to be closely related to the significant shear-induced mixing effect happened in the PB/LPI blend.Graphical abstract
Co-reporter:Yan Zhang, Fenghua Chen, Zhiyong Li, Charles C. Han
Polymer 2012 Volume 53(Issue 2) pp:588-594
Publication Date(Web):24 January 2012
DOI:10.1016/j.polymer.2011.11.051
The reaction induced phase separation behavior was investigated in various epoxy/thermoplastic (TP) blends. Several morphological structures, including the sea-island, dual morphological (epoxy-rich particles may disperse in the TP-rich domains, while TP-rich particles can also have some dispersions in the epoxy-rich phase) or three-layered (TP-rich continuous domains mainly located in the middle part of the sample while outer layers are mostly composed of epoxy-rich matrix) and nodular structure, were observed with the increase of the TP concentrations. In the middle TP concentration ranges, when the TP with low glass transition temperature (Tg) was used, dual morphological structures were formed. While for the epoxy/TP blends with high Tg thermoplastics, three-layered structures were observed. High Tg and the large molecular weight of the TP was considered to cause the dynamic asymmetry, which dominated the phase separation mechanism and formed such an unusual structure. Through the in-situ investigation on time evolution of phase separation process, ubiquitous nature of this formation mechanism of the three-layered structure were discussed, which may have some important implications on the applications of the epoxy/TP blends.
Co-reporter:Jun Luo, Yongri Liang, Jian Yang, Hui Niu, Jin-Yong Dong, Charles C. Han
Polymer 2012 Volume 53(Issue 12) pp:2465-2475
Publication Date(Web):25 May 2012
DOI:10.1016/j.polymer.2012.03.057
In this work, we investigated the effects of liquid–liquid phase separation (LLPS) on the crystallization kinetics and morphology of isotactic polypropylene/poly (ethylene-co-octene) (iPP/PEOc) in-reactor alloy with polarized optical microscopy (POM), differential scanning calorimeter (DSC), scanning electron microscopy (SEM), wide angle X-ray scattering (WAXS) and small angle X-ray scattering (SAXS) methods. Based on crystallization kinetics analysis by Avrami equation, we found that the overall crystallization rate was almost independent on LLPS time, whereas was strongly dependent on crystallization temperature. However, by combination with POM, we found that the LLPS played two opposite roles on the overall crystallization rate, i.e. the nucleation rate decreased and the spherulite growth rate increased as increasing LLPS time. It is due to the nucleation rate was dominated by fluctuation-assisted nucleation mechanism and the growth rate was dominated by diffusion-controlled growth. Furthermore, the spherulite size and PEOc domain size of iPP/PEOc in-reactor alloy were significantly dependent on LLPS time; however, the crystallinity was almost not dependent on LLPS time.Graphical Abstract
Co-reporter:Zhiyong Li, He Cheng, and Charles C. Han
Macromolecules 2012 Volume 45(Issue 7) pp:3231-3239
Publication Date(Web):March 28, 2012
DOI:10.1021/ma202535j
The mechanism of narrowly dispersed latex formation in a surfactant-free emulsion polymerization (SFEP) of styrene in acetone–water was studied by a combination of transmission electron microscopy (TEM) and dynamic light scattering (DLS). The critical nuclei were experimentally observed and the formation of narrowly dispersed PS latex is proved to be originated from competitive growth kinetics. Spherical nuclei were regenerated via a microphase inversion of PS oligomer in a 50% volume fraction acetone–water mixture at 70 °C. They followed a polydispersed log-normal distribution with R̅s ∼ 10.6 nm and δ ∼ 0.298, and the smallest nucleus with Rs ∼ 1.1 nm was similar to critical nuclei, with PS backbone (average chain length ∼6–7) repeat units) inside and sulfate groups to stabilize it at oligomer chain ends. Note that the spherical nuclei are not necessarily narrowly dispersed. Competitive growth kinetics makes smaller nuclei grow much faster than large nuclei in the subsequent polymerization process, resulting in narrowly dispersed PS latex. Time resolved dynamic light scattering (DLS) was used to verify this. Two kinds of PS seed particles which had already grown to the dimension of ⟨Rh⟩ ∼ 300 nm and ∼400 nm were added, separately, into two parallel surfactant-free emulsion polymerization batches of styrene in acetone–water mixture at 70 °C, when the average hydrodynamic radius of PS latex was about ∼20–30 nm. It was found that the size of ∼300 or 400 nm seed particles almost did not change, but the small size PS latex grew rapidly. Narrowly dispersed PS latex was finally obtained in the SFEP system, which supports the competitive growth mechanism proposed by Vanderhoff and co-workers.
Co-reporter:Demiao Lin, He Cheng, Fasheng Zou, Wei Ning, Charles C. Han
Polymer 2012 Volume 53(Issue 6) pp:1298-1305
Publication Date(Web):9 March 2012
DOI:10.1016/j.polymer.2012.01.029
The deformation, breakup and morphology relaxation of a commercially important polycarbonate (PC)/poly(styrene-co-acrylonitrile) (SAN) blend under and after steady shear flow have been studied in situ by combined phase contrast optical microscopy (PCOM), small angle light scattering (SALS) and rheometry. Under steady shear flow, the morphology of PC/SAN blends evolves via repeated deformation, breakup and finally string-like morphology. The data can be qualitatively interpreted with the mode-coupling renormalization group (MCRG) model. At high shear rate, shear-induced mixing effect is found to be saturated and no further shear-induced homogenization can be observed, which may be due to the fact that the experimental conditions (T, C) is far from the critical region and the shear suppression of concentration fluctuations is limited. Upon cessation of shear, different relaxation mechanisms are found. For low shear rate, the anisotropic ellipsoids retract to isotropic domains after shear cessation; while for higher shear rate, the string-like pattern breaks into necklace-like structure first and then the aligned structure relaxes to an isotropic distribution via diffusion process. The slow coarsening process upon cessation of shear is attributed to high viscosity of PC matrix and viscoelastic effects.PCOM and SALS images of PC/SAN 7/3 blends after shear cessation from steady state sheared at 5 s−1.
Co-reporter:Chuanzhuang Zhao, Guangcui Yuan, and Charles C. Han
Macromolecules 2012 Volume 45(Issue 23) pp:9468-9474
Publication Date(Web):November 16, 2012
DOI:10.1021/ma301747s
Poly(N-isopropylacrylamide) (PNIPAM) microgels are adsorbable to the surface of polystyrene (PS) microspheres in the experimental temperature range (25–40 °C) and can induce aggregation of microspheres through the bridging mechanism. The bridging mechanism proceeds in two elementary steps: the first is an adsorption (negligible desorption relatively) of free microgel to one microsphere surface, and the next is a reversible connection of the adsorbed microgel to another microsphere surface. The surface coverage is found as an important factor in triggering the stabilization, aggregation, and gelation of the mixtures. And most importantly, the nonnegligible dynamic disconnection of a bridge is the essential prerequisite for structure or state transition. For mixtures with the same concentration of microsphere, depending on the concentration of microgel, various transitions can be induced by changing temperature, including the transition from a weaker gel to a stronger gel, from a fluid to a bridging gel and from a depletion gel to a bridging gel.
Co-reporter:Jingjing Yang, Yongri Liang, Jun Luo, Chuanzhuang Zhao, and Charles C. Han
Macromolecules 2012 Volume 45(Issue 10) pp:4254-4261
Publication Date(Web):April 30, 2012
DOI:10.1021/ma202505f
In this work, we investigated the structure and morphology formation in crystalline–crystalline diblock copolymer of poly(l-lactide)-block-poly(ethylene glycol) (PLLA-b-PEG) on different length scales with optical microscopy (OM), atomic force microscopy (AFM), synchrotron time-resolved small-angle X-ray scattering (TR-SAXS) and wide-angle X-ray scattering (WAXS) methods. The PLLA-b-PEG copolymer with 5000 of number-average of molecular weight of PLLA and PEG blocks was used in this work. The structure and morphology of PLLA-b-PEG copolymers were formatted by a two-step crystallization process: i.e., the PLLA block crystallized fully at 110 °C in the first step, and then the PEG block crystallized fully at 30 °C in the second step. The OM, AFM, and SAXS results indicated that the PEG block crystallized in the multilength scales amorphous regions confined by PLLA crystals. The PEG block crystallized not only in the interlamellar regions of PLLA crystals, but also in the interfibrillar regions of PLLA. However, the subsequent crystallization of PEG block did not alter the foregoing spherulitic morphology of PLLA on the micrometer scale.
Co-reporter:Fasheng Zou, Xia Dong, Wei Liu, Jian Yang, Demiao Lin, Aimin Liang, Wei Li, and Charles C. Han
Macromolecules 2012 Volume 45(Issue 3) pp:1692-1700
Publication Date(Web):January 23, 2012
DOI:10.1021/ma2021562
The rheology of near- and off-critical elastomeric blends of polybutadiene (PB)/ low vinyl content polyisoprene (LPI) has been studied as a function of temperature, heating rate, and shear frequency. Depending on the composition, near or far away from the critical point, blends showed different behaviors in several aspects: temperature ramp curves, shift of the apparent binodal and spinodal points under oscillatory shear at the given frequency and strain amplitude. The composition dependent rheological responses are interpreted by the differences in the amplitude of the critical fluctuation near the phase boundary and in the shear induced mixing mechanisms between near- and off-critical blends. For near-critical blends, the critical fluctuation is large enough to induce a considerable extra stress when the blend is still in the miscible state. As a result, a heating rate independent upturn of G′ can be observed and the apparent spinodal point can be greatly shifted through the strong suppression of the large critical fluctuations. In contrast, for off-critical blends, the critical fluctuations in the metastable region are relatively small and there is competition between the phase separation kinetics and the heating rate. Therefore, the blend displayed a heating rate dependent apparent binodal point and a large shift of the apparent binodal point but a moderate shift of the spinodal point under oscillatory shear. By lowering or extrapolating the measured frequency to a very small value (0.1 rad/s in this study) for both binodal and spinodal points, the rheologically determined phase diagram is consistent with the static results obtained by optical microscopy observations.
Co-reporter:Weichao Shi;He Cheng;Fenghua Chen;Yongri Liang;Xuming Xie
Macromolecular Rapid Communications 2011 Volume 32( Issue 23) pp:1886-1890
Publication Date(Web):
DOI:10.1002/marc.201100490
Abstract
Spherulitic patterns usually form in the single process of crystallization in polymer blends. But when phase separation intervenes under deep quench, the radial growth of the initial spherulitic patterns tends to invert into concentric alternating crystalline-/amorphous-rich ring structures. Within crystalline-rich regions, lateral lamellae orient in the tangential direction rather than in the usual radial direction. We demonstrate the determining factor for this first observed phenomenon is the concentration deviation enhanced phase separation dynamics at the growth interface of crystals.
Co-reporter:Fuyong Bi;Aihua He;Huayi Li;Youliang Hu;Zhiyuan He;Charles C Han
Polymer International 2011 Volume 60( Issue 8) pp:1167-1172
Publication Date(Web):
DOI:10.1002/pi.3100
Abstract
MgCl2/TiCl4/diether is a fifth-generation Ziegler–Natta catalyst for the commercial polymerization of propylene. The outstanding features of this catalyst are the high activity and high isotacticity for propylene polymerization without using an external electron donor. In this study, we explored the copolymerization of propylene and 1-octene with MgCl2/TiCl4/diether catalyst. It was found that MgCl2/TiCl4/diether catalyst showed higher polymerization activity and led to greater 1-octene content incorporation, compared with a fourth-generation Ziegler–Natta catalyst (MgCl2/TiCl4/diester). With an increase in 1-octene incorporation in polypropylene chains, the melting temperature, glass transition temperature and crystallinity of the copolymers decreased distinctly. The microstructures of the copolymers were characterized using 13C NMR spectroscopy, and the copolymer compositions and number-average sequence lengths were calculated from the dyad concentration and distribution. This result is very important for the in-reactor polyolefin alloying process, especially for the case of a single catalyst and two-step (or two-reactor) process. Copyright © 2011 Society of Chemical Industry
Co-reporter:Yan Zhang, Weichao Shi, Fenghua Chen, and Charles C. Han
Macromolecules 2011 Volume 44(Issue 18) pp:7465-7472
Publication Date(Web):September 6, 2011
DOI:10.1021/ma201318g
A thermoplastic polysulfone was used to blend with epoxy resin, and both the curing reaction and phase separation of the epoxy/polysulfone blend were investigated. Polysulfone did not alter the mechanism of curing reaction; however, it did depress the reaction rate. The details of the dynamically asymmetric phase separation, which was caused by the large differences in viscoelastic properties between epoxy and polysulfone component, were observed and studied. During the structure evolution, volume-shrinking behavior of the dynamically slow polysulfone component always existed even at fairly low (but still above the entanglement concentration) concentrations. More interestingly, when the curing temperature was higher than the glass transition temperature of polysulfone, volume shrinking with the consequence of layered structure formation was also observed as long as the viscoelastic asymmetry was maintained. These results indicated the generality of the mechanism of the dynamically asymmetric phase separation in this type of reactive system. Also, the influence of curing temperature was studied, and it was found that phase separation was promoted more than the curing reaction as the temperature was increased.
Co-reporter:Jing Jin, Chuanzhuang Zhao, Jiang Du, and Charles C. Han
Macromolecules 2011 Volume 44(Issue 11) pp:4326-4334
Publication Date(Web):May 6, 2011
DOI:10.1021/ma200194c
This work focuses on the effect of the unique molecular structure of OBC (olefin block copolymer) constituted by soft blocks and hard blocks on the compatibility of OBC/iPP (isotactic polypropylene) blends. Two OBCs with high and low octene content were selected to blend with iPP. The thermal behavior, morphology, and kinetics of crystallization of the binary blends were studied systematically. The variation in octene content of the OBCs caused a dramatic difference in their own mesophase separation as well as their compatibility with iPP in blends. As the octene content increased, mesophase separation of OBC became more and more dominant, with the strong repulsive interaction between the hard and soft blocks of OBC and the coupled fact that the majority of the soft blocks are more compatible with iPP, resulting in its better compatibility with iPP. This was proved by smaller dispersed domain size, better interfacial adhesion, and faster crystallization kinetics. On the other hand, we also found that annealing time was important in controlling the superstructure in blends. There is a possible scalability of the mesophase separation of OBC on the compatibility and superstructure of the OBC/iPP binary blends. According to our results, it is reasonable to obtain a systematic profile to adjust the compatibility as well as the superstructure to satisfy different mechanical requirement by regulating octene content in the OBC and the annealing condition of the blends.
Co-reporter:Jun Luo, Yongri Liang, Jingjing Yang, Hui Niu, Jin-Yong Dong, Charles C. Han
Polymer 2011 Volume 52(Issue 20) pp:4590-4599
Publication Date(Web):12 September 2011
DOI:10.1016/j.polymer.2011.07.047
The nucleation and lamellar growth mechanisms of nascent isotactic polypropylene/poly(ethylene-co-octene) (N-iPP/PEOc) in-reactor alloy were investigated with temperature-resolved synchrotron small angle X-ray scattering (SAXS), differential scanning calorimeter (DSC) and polarized optical microscopy (POM) methods. We have observed two crystallization peaks (fractionated crystallization behavior) during cooling process in N-iPP/PEOc in-reactor alloy. We also determined that the crystallinities from that two crystallization peaks were dependent on liquid–liquid phase separation (LLPS) time with t0.10 and t−0.28, respectively. It was explained that the fractionated crystallization behavior in the N-iPP/PEOc in-reactor alloy system was caused by crystal nucleation occurring in the iPP rich domain by heterogeneous nucleation and at interface of iPP and PEOc rich domains by the fluctuation assisted nucleation. The fluctuation assisted nucleation only occurred at interface of iPP and PEOc domains by concentration fluctuation through the coupling of liquid–liquid spinodal decomposition and the cross-over to crystal nucleation process. Both lamellar crystals formations from heterogeneous and fluctuation assisted nucleation in N-iPP/PEOc were probed by temperature-resolved SAXS during cooling process. Our results provide the physical model for the multiple nucleation and crystal growth mechanisms in the multi-component, multi-phase polymer systems such as in-reactor alloy or blend.
Co-reporter:Jing Jin, Jiang Du, Hongyu Chen, Charles C. Han
Polymer 2011 Volume 52(Issue 26) pp:6161-6172
Publication Date(Web):13 December 2011
DOI:10.1016/j.polymer.2011.11.005
This work mainly focused on the nucleation behavior in iPP/OBC (isotactic polypropylene/polyolefin block copolymers) blends with two distinct OBCs. The influence of composition and molecular structure of the OBC component on the crystallization kinetics of the blends was investigated systematically with the aim to better understand the interplay between the two coupled phase transitions in the blends: macrophase separation and crystallization. The isothermal crystallization kinetics showed component and composition dependence in iPP/OBC blends. All the blends in the studied range have enhanced nucleation ability of iPP than the pure iPP under identical conditions. Furthermore, the distinct macrophase separation morphology resulting from the different compatibility between the various OBCs and iPP caused remarkable diversity between the blends: the nuclei density is qualitatively higher (or the nucleation rate is qualitatively faster) in the more compatible blends, and this enhancement of nucleation can be depressed by imposing a macrophase separation process before crystallization. The crystal nuclei from the phase separated matrix were preferentially formed at the interface of the phase domains, and then grew toward and into the iPP-rich phase. It is postulated that the increased nuclei density and/or nucleation rate followed the fluctuation-assisted nucleation mechanism: the enhanced concentration fluctuation at the interfacial area created by the spinodal decomposition played an important role in the nucleation behavior of iPP/OBC blends. The decreased interface areas with increased domain sizes after deeper phase separation, coupled with a more depressed concentration fluctuation, are responsible for lower nuclei density after long time annealing for phase separation.
Co-reporter:Zhiyong Li, He Cheng, Junyu Li, Jinkun Hao, Li Zhang, Boualem Hammouda, and Charles C. Han
The Journal of Physical Chemistry B 2011 Volume 115(Issue 24) pp:7887-7895
Publication Date(Web):May 16, 2011
DOI:10.1021/jp203777g
Author: Because of the closed-loop phase diagram of tetrahydrofuran (THF)–water mixture, THF aqueous solution naturally exhibits concentration fluctuations near the phase boundary. Besides the fast mode induced by concentration fluctuations, the 4.5% mole fraction THF aqueous solution is also characterized by a slow mode. The existence of a trace amount of butylhydroxytoluene (BHT) antioxidant in commercial THF strongly influences the slow mode in 4.5% mole fraction THF aqueous solution. A core–shell structure with a BHT core and a shell made from THF-rich THF–D2O mixture was identified by the combination of dynamic laser light scattering (DLS) and small-angle neutron scattering (SANS). BHT is hydrophobic, stabilized by a THF-rich domain in THF aqueous solution and acts as a tracer to make the large-scale structure (slow mode) “visible” through SANS because of its larger contrast with the solvent. In contrast, this large-scale structure was almost not detectable by SANS when BHT was removed from the THF–D2O mixture. Combined UV–vis, DLS, and static light scattering (SLS) indicated that slow-moving objects do exist and that their sizes almost do not change, but their concentration decreases to a small but nonzero value at the infinite dilution limit. The origin of the elusive large-scale structure at zero BHT concentration is still not clear, but it might be associated with some hydrophobic impurities or nanobubbles. However, a polydisperse sphere model of ∼8.5% mole fraction THF–D2O mixture can fit the structure with a radius of ∼100 nm, which gives the temperature-dependent low-q SANS profiles of 4.5% mole fraction THF aqueous solution at zero BHT concentration.
Co-reporter:Ye Huang, He Cheng, and Charles C. Han
Macromolecules 2011 Volume 44(Issue 12) pp:5020-5026
Publication Date(Web):June 2, 2011
DOI:10.1021/ma200273u
A relatively narrow molecular weight dispersed regioregular poly(3-hexylthiophene) (rr-P3HT) fraction was obtained through the removal of low molecular weight fraction by Soxhlet extraction and the high molecular weight fraction by ultracentrifugation. Combined static (SLS) dynamic (DLS) light scattering and TEM measurements were conducted to study its conformation variation with temperature. An upper critical solution temperature (UCST) type of phase diagram with a loose aggregate to unimer transition process is observed in the heating process. The dynamic equilibrium between unimer, with ⟨Rh⟩ ∼ 4 nm, and loose aggregate, with ⟨Rh⟩ ∼ 55 nm, shifts to the unimer side with temperature because the loose aggregate, which consisted of bundles of unimer chains, are destroyed and dissembled by thermal energy. TEM observation was used to verify our LS results. It is found that the presence of loose aggregate in solution is crucial for the formation of interconnected and long nanofibrils in film morphology as loose aggregate embraces interchain interaction between conjugated polymer chains. Independent nanofibrils come from the crystallization of unimers during solvent evaporation process. Therefore, the percentage of interconnected nanofibrils decreases with drop-casting temperature. In the cooling process, this kinetic of self-assemble from unimers into loose aggregates in the THF solution is very slow. Taking advantage of this slow kinetic, we studied the time dependence of the structures formation at 10 °C. The unimers to loose aggregates to spherical associates to precipitates transition processes are monitored. This kinetic mapping of the unimer to loose aggregate equilibrium to nonequilibrium large scale associates is essential to optimize the nanofibrils’ percentage and structure before the drop-casting process.
Co-reporter:Huarong Nie, Junxing Li, Aihua He, Shanshan Xu, Qingsong Jiang and Charles C. Han
Biomacromolecules 2010 Volume 11(Issue 8) pp:
Publication Date(Web):July 23, 2010
DOI:10.1021/bm100505j
Co-reporter:Yan Zhang, Fenghua Chen, Weichao Shi, Yongri Liang, Charles C. Han
Polymer 2010 Volume 51(Issue 25) pp:6030-6036
Publication Date(Web):26 November 2010
DOI:10.1016/j.polymer.2010.10.027
In an epoxy/polysulfone blend, the reaction-induced phase separation behavior and the final morphology were investigated. Three distinct morphological structures were obtained. Sea-island and nodular structures were observed at lower and higher polysulfone contents, respectively. A three-layered structure was obtained in the middle polysulfone concentration range. In order to understand the formation of three-layered structure, phase separation process was studied using time-resolved light scattering, phase-contrast optical microscope and scanning electron microscope. Bicontinuous structure formed uniformly in the whole sample at the beginning of phase separation. After the phase structure grew for a certain time, large domains formed and developed. Then, the large epoxy-rich domains gradually flew to the outer space of the sample film. This process assisted the formation of the three-layered structure. The mechanism of the formation of the three-layered structure was discussed based on the different viscoelastic properties of the components.
Co-reporter:Yonghua Yao, Xia Dong, Chenggui Zhang, Fasheng Zou, Charles C. Han
Polymer 2010 Volume 51(Issue 14) pp:3225-3229
Publication Date(Web):24 June 2010
DOI:10.1016/j.polymer.2010.05.027
The phase diagram of an isotactic polypropylene/poly(ethylene-octene) copolymer (iPP/PEOc) blend system was investigated using phase contrast optical microscopy, laser light scattering and differential scanning calorimetry (DSC). The sample goes through immiscible (opaque) region to transparent region (seemingly miscible) and back to immiscible (opaque) again as temperature increases through 300 °C region. But it turns out that this is not a real one phase region. It is caused by a temperature dependent inversion of refractive indices between the two component polymers, which can be easily misinterpreted as a miscible region between an upper critical solution temperature (UCST) state and a lower critical solution temperature (LCST) state. With a proper interpretation and analysis of this refractive index inversion, the UCST phase diagram of this iPP/PEOc blend system has been obtained.
Co-reporter:Qingzeng Zhu, Charles C. Han
Polymer 2010 Volume 51(Issue 4) pp:877-882
Publication Date(Web):15 February 2010
DOI:10.1016/j.polymer.2009.12.033
Well architectured polyurethanes containing fluorine are expected to be applied in medical devices as well as other fields. A telechelic polyurethane end-capped with perfluoropolyether segments was prepared from polyether glycol as a soft segment, 4, 4′-methylene-bis-(phenylisocyanate), and monofunctional perfluorinated oligomer. The telechelic polyurethane was studied by Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), contact angle and atomic force microscopy (AFM). XPS results indicated that the surface of the fluorine containing polyurethane was enriched with fluorine component. It exhibited a hydrophobic property with a water contact angle of 113°. The polyurethane terminated with perfluoropolyether segments showed a better thermal stability. A mechanism was proposed to explain thermal decomposition of polyurethanes. DSC results suggested that the tail-like perfluoropolyether segments would disrupt main chain packing, then raise crystallization potential barrier, and the perfluoropolyether segments did not affect the bulk microphase-separated structure.
Co-reporter:Huarong Nie, Aihua He, Bing Jia, Fan Wang, Qingsong Jiang, Charles C. Han
Polymer 2010 Volume 51(Issue 15) pp:3344-3348
Publication Date(Web):8 July 2010
DOI:10.1016/j.polymer.2010.05.014
Electrospun nanofibrous membrane is an approved drug carrier. However, the radionuclide carrier used an electrospun membrane is rare. In this study, Poly(lactide-co-glycolide)(PLGA) nanofibrous nonwovens were prepared through electrospinning technology, and then surface modification of the nonwoven was performed to stably conjugate the radioisotope with the fibrous membrane. A novel PLGA nanofibrous nonwoven conjugated with radioactive yttrium 90Y for tumor internal radiotherapy was prepared for the first time. Evaluation of the stability of the radioisotope indicated that the leakage of 90Y from the PLGA membranes can be neglected after 24 h incubation in saline. The retention of 90Y on the PLGA membrane was 75% when five half lives of 90Y expired and the vast majority of radioactive decay had occurred. This labeled nanofibrous membrane function as a novel radio-medical appliance with excellent surface hydrophilic and mechanical properties that can be directly implanted into the lesions not only to locally kill the cancerous cells but also to play the anti-adhesion role at where surgical procedures have been made to remove the tumor tissue.
Co-reporter:Haiqing Hu, Junyu Li, Chenggui Zhang, Charles C. Han
Polymer 2010 Volume 51(Issue 20) pp:4619-4626
Publication Date(Web):17 September 2010
DOI:10.1016/j.polymer.2010.07.031
The phase behavior of PEB/PES (poly(ethylene-co-styrene)/poly(ethylene-co-butene)) blend system was studied by time resolved laser light scattering with both wide angle and small angle laser light scattering. The phase separation kinetics show that the phase diagram of this system is a closed loop with both lower critical solution transition (LCST) and upper critical solution transition (UCST), which is inconsistent with the results obtained by optical microscope we reported before. All of the phase separation processes including early, middle and late stages have been studied. The coarsening behavior of the blend was characterized in terms of the time change of the maximum intensity Im, and the magnitude of the scattering vector qm, at which the intensity becomes maximum. The theory to interpret the phenomena has been studied by many researchers, and it is waiting for further theoretical systematic research.
Co-reporter:Jing Jin, Jiang Du, Qinghua Xia, Yongri Liang, and Charles C. Han
Macromolecules 2010 Volume 43(Issue 24) pp:10554-10559
Publication Date(Web):November 19, 2010
DOI:10.1021/ma102075c
This paper investigates the effect of mesophase separation on the crystallization behavior of olefin block copolymers (OBCs) with different octene contents, which were synthesized by chain shuttling technology. Crystallization always occurs simultaneously but competitively with mesophase separation in OBCs. Because of the reason that the crystallization temperature is lower than the mesophase separation temperature for the OBCs, the mesophase separation can start first; large portions of the crystallizable hard blocks are confined in the mesophase-separated domains and could not contribute to the formation of radial lamellar stacks. In addition, the mesophase separation creates a stereo-hindrance effect; crystal lamellae could only grow through the interstitial space between the dispersed domains. As a result, large and compact crystals could not be formed. As the octene content increased in the sample, mesophase separation becomes more and more dominant, and the crystal morphology degrades sharply from spherulites to fragmentary lamella structures. It is found that increasing the annealing time during development of the mesophase-separated structure has a similar effect to increasing the octene content in the sample. However, all of the OBCs can form nearly the same crystalline morphology if the mesophase separation is suppressed, from which we can postulate that the nature of crystallization due to the crystallizable hard blocks in OBCs should be similar.
Co-reporter:Ye Huang, He Cheng, and Charles C. Han
Macromolecules 2010 Volume 43(Issue 23) pp:10031-10037
Publication Date(Web):November 10, 2010
DOI:10.1021/ma102168a
The structure evolution of regioregular poly(3-hexylthiophene) (P3HT) in THF dilute solution and its influence on thin film morphology were studied by a combination of static and dynamic laser light scattering (SLS and DLS) and transmission electron microscopy (TEM). Most P3HT is not directly soluble in THF at room temperature. A thermal treatment at high temperature effectively redisperses P3HT microsized aggregates, and introduces two modes in DLS measurement. The fast mode with ⟨Rh⟩f ∼ 4 nm is P3HT unimer coil, while the slow mode with ⟨Rh⟩s∼ 90 nm is P3HT associate. The linear relationship between ⟨Γ⟩ and q2 passing through origin indicated both modes are diffusive. DLS showed the percentage of large associates is increasing, and that of the unimer coils is decreasing with temperature. The ratio, ⟨Rg⟩s/⟨Rh⟩s ∼ 0.8, indicates the associates are closely packed spherical in shape. The structure of P3HT in dilute solution greatly influences its morphology on thin films. We found that the memory of chain conformation and association in solution are carried into drop casted film, TEM examination of drop casted thin film morphology clearly indicated that the densely packed spherical associates are elastic with its morphology unchanged during evaporation process because of its visco-elastic nature; while the P3HT unimer coils assemble and crystallize into nanofibrils. The nanofibrils' percentage decreases with temperature because the coexistence equilibrium between P3HT unimer and spherical associates shifts greatly to the associates side. However, this apparent equilibrium of unimer−associate is in a metastable state. Over a long time, the system will gradually form larger and more stable aggregates which are in equilibrium with unimers at room temperature. Overall, after a proper thermal treatment in solution, it suppresses aggregates formation and increases electronic and opto-physics properties when drop casting is conducted at room temperature.
Co-reporter:Jinkun Hao, Zhiyong Li, He Cheng, Chi Wu, and Charles C. Han
Macromolecules 2010 Volume 43(Issue 22) pp:9534-9540
Publication Date(Web):October 26, 2010
DOI:10.1021/ma101659c
Effects of pH, dodecyl, and PEO contents as well as the method of preparing the solution on the formation of the unimolecular micelles (unimer micelle) or aggregates made of poly(acrylic acid)-graft-poly(ethylene oxide)-graft-dodecyl (PAA-g-PEO-g-dodecyl) and PAA-g-dodecyl have been studied by a combination of static and dynamic laser light scattering (SLS and DLS). It revealed that: in most cases, these copolymers tend to form interchain associates; while low pH value, proper high dodecyl content and fast switch rate of solvent quality promote intrachain association. These phenomena of the system being trapped in a metastable state can be mainly attributed to its kinetic pathway: the factors mentioned earlier can enhance the initial intrachain contraction, leading to τc (interaction time) ≪ τe (entanglement time) for the two interaction intrachain globules. So they behave like tiny “elastic balls” and their further merge/fusion become nearly impossible during their interaction time (τc). In this way, the copolymer system is trapped in the metastable, unimer micelle state. The interplay of τc and τe in the formation of metastable unimer micelles or stable aggregates has been discussed in detail.
Co-reporter:Jinkun Hao, Guangcui Yuan, Weidong He, He Cheng, Charles C. Han and Chi Wu
Macromolecules 2010 Volume 43(Issue 4) pp:2002-2008
Publication Date(Web):January 29, 2010
DOI:10.1021/ma9025515
Poly(acrylic acid)-graft-poly(ethylene oxide) (PAA-g-PEO) in aqueous solutions shows one fast and one slow relaxation mode in dynamic light scattering (DLS), but the mixture of PAA and PEO (PAA/PEO) in aqueous solution only has a single fast mode. The effects of pH, polymer concentration, and salt concentration on these two modes have been investigated using laser light scattering (LLS), viscometry, and rheological measurements. Our results showed that the hydrogen bonding between carboxylic group and ether oxygen led to the formation of large complexes among PAA-g-PEO chains, which were absent between PAA and PEO chains in PAA/PEO aqueous solutions. The addition of formamide can break these interchain complexes because the hydrogen bonding between formamide and PAA segment is stronger than that between PEO and PAA segment. Thermodynamically speaking, the formation of hydrogen bonds among PAA-g-PEO chains leads to a less entropy loss than that between PAA and PEO chains in PAA/PEO aqueous solution, because in the former case PEO is already chemically connected to PAA backbone. Therefore, the same enthalpy gain is sufficient to compensate the entropy loss in PAA-g-PEO aqueous solution relative to that in PAA/PEO aqueous solution, resulting in large interchain PAA-g-PEO complexes.
Co-reporter:Wanling Wu, Guangcui Yuan, Aihua He and Charles C. Han
Langmuir 2009 Volume 25(Issue 5) pp:3178-3183
Publication Date(Web):February 9, 2009
DOI:10.1021/la803580g
For materials containing fluorine, it has been generally accepted that fluorinated segments or end groups tend to aggregate in the outer surface because of the low surface energy, which endows the fluorinated materials with special surface properties such as self-cleaning, superhydrophobicity, and so forth. However, for the electrospun fibrous membranes of polyurethane elastomers containing perfluoropolyether segments (FPU), abnormal fluorine aggregations in the core of the electrospun fibers were observed. The XPS analysis indicated a rather low fluorine content at the surface of the electrospun FPU fibers. Further study with dynamic light scattering and fluorescence showed that FPU chains can form aggregates in the concentrated solution. Therefore, it can be deduced that the rapid evaporation of solvent and fast formation of fibers during the electrospinning process could result in the freeze-in of the aggregated chain conformation and the depletion of fluorine units on the surface of the electrospun FPU fibers.
Co-reporter:Huarong Nie, Aihua He, Wanling Wu, Jianfen Zheng, Shanshan Xu, Junxing Li, Charles C. Han
Polymer 2009 50(20) pp: 4926-4934
Publication Date(Web):
DOI:10.1016/j.polymer.2009.07.043
Co-reporter:Shanshan Xu, Junxing Li, Aihua He, Wenwen Liu, Xingyu Jiang, Jianfen Zheng, Charles C. Han, Benjamin S. Hsiao, Benjamin Chu, Dufei Fang
Polymer 2009 50(15) pp: 3762-3769
Publication Date(Web):
DOI:10.1016/j.polymer.2009.06.009
Co-reporter:Tongchen Sun, Fenghua Chen, Xia Dong, Yong Zhou, Dujin Wang, Charles C. Han
Polymer 2009 50(11) pp: 2465-2471
Publication Date(Web):
DOI:10.1016/j.polymer.2009.03.048
Co-reporter:Yan Wang, Kun Meng, Song Hong, Xuming Xie, Chenggui Zhang, Charles C. Han
Polymer 2009 50(2) pp: 636-644
Publication Date(Web):
DOI:10.1016/j.polymer.2008.11.041
Co-reporter:Ruoyu Zhang, Xia Dong, Xin Wang, He Cheng and Charles C. Han
Macromolecules 2009 Volume 42(Issue 7) pp:2873-2876
Publication Date(Web):March 18, 2009
DOI:10.1021/ma8028166
Co-reporter:Jiang Du;Xiaohua Zhang
Journal of Polymer Science Part B: Polymer Physics 2009 Volume 47( Issue 2) pp:166-172
Publication Date(Web):
DOI:10.1002/polb.21627
Abstract
The new fluctuation-assisted mechanism for nucleation and crystallization in the isotactic polypropylene/poly(ethylene-co-octene) alloy has been studied. We found that the liquid–liquid phase separation (LLPS) had a dominant influence on the crystallization kinetics through the nucleation process. After LLPS, the nucleation of crystallization mainly occurred at the interface of the phase-separated domains. It is because that the concentration fluctuations of the LLPS induced the motion of polymer chains and possibly some segmental alignment and/or orientation in the concentration gradient regions through interdiffusion, which could assist the formation of nuclei for crystallization. In other words, the usual nucleation energy barrier could be overcome (or at least partially) by the concentration fluctuation growth of LLPS in the unstable regions. This could be viewed as a new kind of heterogeneous nucleation and could be an addition to the regular nucleation and growth mechanism for crystallization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 166–172, 2009
Co-reporter:Wanling Wu, Qingzeng Zhu, Fengling Qing and Charles C. Han
Langmuir 2009 Volume 25(Issue 1) pp:17-20
Publication Date(Web):November 24, 2008
DOI:10.1021/la803089y
Surface geometrical microstructure and low surface free energy are the two most important factors for a self-cleaning surface. In this study, multiform geometrical microstructured surfaces were fabricated by casting and electrospinning polyurethanes with and without low surface energy segments. The effect of low surface energy on water repellency was evaluated. Low surface energy seems to make a more significant contribution to the static wetting behavior than do dynamic properties such as the improvement of sliding behavior. Sucking disk behavior was brought forward to explain the pinning state of a water droplet on hydrophobic surfaces with high water contact angles (>150°). A better understanding of the relationship between the static contact angle and the dynamic sliding property was provided.
Co-reporter:Pingli Wang, Kun Meng, He Cheng, Song Hong, Jinkun Hao, Charles C. Han, Harald Haeger
Polymer 2009 50(9) pp: 2154-2160
Publication Date(Web):
DOI:10.1016/j.polymer.2009.02.040
Co-reporter:Song Hong, Xiaohua Zhang, Ruoyu Zhang, Jiang Zhao and Charles C. Han
Macromolecules 2009 Volume 42(Issue 12) pp:4349-4351
Publication Date(Web):May 6, 2009
DOI:10.1021/ma802676f
Co-reporter:Zhong-Xing Zhang, Jinkun Hao, Ping Xie, Xiaojing Zhang, Charles C. Han and Rongben Zhang
Chemistry of Materials 2008 Volume 20(Issue 4) pp:1322
Publication Date(Web):January 10, 2008
DOI:10.1021/cm071602l
A high-molecular-weight and well-defined ladder polyphenylsilsesquioxane (Ph-LPSQ) was synthesized via a new three-step approach: monomer self-organization in solution, lyophilization, and surface-confined polycondensation. A ladder superstructure, which served as a template to direct the polycondensation, was self-assembled from the 1,3-diphenyl-tetrahydroxy-disiloxane monomer (M) in acetonitrile solution. Following that, it was lyophilized to form a thin layer on the inner surface of a flask. Subsequently, polycondensation of the ordered monomeric thin layer was performed under a triethylamine (TEA) atmosphere. This strategy increased the ladder regularity of the Ph-LPSQ by preventing common complications faced in solution polycondensation of silanol-containing monomers, such as cyclization and gelation side reactions. 29Si NMR analysis showed a very narrow peak (peak width at half-height, w1/2 = 2.5 ppm) at δ = –78.5 (corresponding to a Ph-SiO3/2unit), indicating a high degree of regularity of the polymer structure.
Co-reporter:Fenghua Chen;Xin Wang;Xiaojuan Zhao;Jingang Liu;Shiyong Yang
Macromolecular Rapid Communications 2008 Volume 29( Issue 1) pp:74-79
Publication Date(Web):
DOI:10.1002/marc.200700568
Co-reporter:Hong Yang, Bo Li, Ke Wang, Tongch en Sun, Xin Wang, Qin Zhang, Qiang Fu, Xia Dong, Charles C Han
European Polymer Journal 2008 Volume 44(Issue 1) pp:113-123
Publication Date(Web):January 2008
DOI:10.1016/j.eurpolymj.2007.10.028
In this article, the rheological properties of polypropylene (PP)/ethylene–propylene–diene terpolymer (EPDM)/silicon dioxide (SiO2) ternary composites were systematically investigated. Two kinds of nano-SiO2 particles (with hydrophobic (denoted as A-SiO2) or hydrophilic (denoted as B-SiO2)) as well as two processing methods (one-step or two-step) were first employed to prepare PP/EPDM/SiO2 ternary composites. Then the deep mixing and morphology evolution of polymer composite with mixing time were assessed by rheological method, on the focus of formation of filler-network, and compared with scanning electron microscopy (SEM) observations. Linear viscoelastic behavior was observed for PP/EPDM and PP/SiO2 binary system, showing no evidence of the formation of filler-network structure. However, a solid-like rheological behavior, which was attributed to the formation of the filler-network structure as confirmed by SEM observation, could be observed in some PP/EPDM/SiO2 ternary systems, depending on the SiO2 surface property, processing method and EPDM content. It seemed that SiO2 with hydrophilic surface was necessary for the formation of filler-network in PP/EPDM/SiO2 ternary system. Besides, two-step processing method made the solid-like behavior occurred at an earlier stage compared with that of a one-step processing method, also, the higher elastomer content facilitated the formation of the filler-network structure. The results were in good agreement with those reported in our previous publications [Yang H, Zhang Q, Guo M, Wang C, Du R, Fu Q. Polymer 2006;47:2106] [Yang H, Zhang X, Qu C, Li B, Zhang L, Zhang Q, et al. Polymer 2007;48:860].
Co-reporter:Huarong Nie, Aihua He, Jianfen Zheng, Shanshan Xu, Junxing Li and Charles C. Han
Biomacromolecules 2008 Volume 9(Issue 5) pp:
Publication Date(Web):April 24, 2008
DOI:10.1021/bm701349j
As a natural biopolymer, sodium alginate (SA) has been widely used in the biomedical field in the form of powder, liquid, gel, and compact solid, but not in the form of nanofiber. Electrospinning is an effective method to fabricate nanofibers. However, electrospinning of SA from its aqueous solution is still a challenge. In this study, an effort has been made to solve this problem and find the key reasons that hinder the electrospinning of alginate aqueous solution. Through this research, it was found that pure SA nanofibers could be fabricated successfully by introducing a strong polar cosolvent, glycerol, into the SA aqueous solutions. The study on the properties of the modified SA solution showed that increasing glycerol content increased the viscosity of the SA solution greatly and, meanwhile, decreased the surface tension and the conductivity of the SA solution. The rheological results indicated that the increase in glycerol content could result in the enhanced entanglements of SA chains. Two schematic molecular models were proposed to depict the change of SA chain conformation in aqueous solution with and without glycerol. The main contribution of glycerol to the electrospinning process is to improve the flexibility and entanglement of SA chains by disrupting the strong inter- and intramolecular hydrogen bondings among SA chains, then forming new hydrogen bondings with SA chains.
Co-reporter:Song Hong, Xiaohua Zhang, Ruoyu Zhang, Li Wang, Jiang Zhao and Charles C. Han
Macromolecules 2008 Volume 41(Issue 7) pp:2311-2314
Publication Date(Web):March 12, 2008
DOI:10.1021/ma7025379
Co-reporter:Ruoyu Zhang, He Cheng, Chenggui Zhang, Tongchen Sun, Xia Dong and Charles C. Han
Macromolecules 2008 Volume 41(Issue 18) pp:6818-6829
Publication Date(Web):August 28, 2008
DOI:10.1021/ma800646s
Viscoelastic polymer blends of polybutadiene (PB)/low vinyl content polyisoprene (LPI), with a lower critical solution temperature (LCST), show interesting rheological behaviors in temperature ramp measurements. In this report, a systematic study has been carried out, and the underlying physics has been investigated for the storage modulus G′ at various temperatures and shear frequencies as the system passes through the binodal and the spinodal phase boundary lines. We considered the nucleation mechanism, spinodal fluctuations, shear induced mixing, and rheological models in the interpretation of these interesting phenomena. Shear induced mixing is varied in our system, and the frequency dependence is obvious. Competition between the kinetics of the nucleation process and the droplet growth process has a prominent effect on the storage modulus for samples of noncritical compositions, while for samples with near-critical compositions the morphological evolution is responsible for the viscoelastic changes. Time-dependent experiments provide important information about morphological evolution at different temperatures. The region where fluctuations play a dominant effect on G′ can be discerned from our treatment of putting G′ and {G′(ω)/[G′′2(ω)T]}2/3 in the same reference frame. On the basis of the results from both heating and cooling processes, it seems that there also exist competition between fluctuations and interfacial gradient on the determination of the value of G′.
Co-reporter:Fenghua Chen, Tongchen Sun, Song Hong, Kun Meng and Charles C. Han
Macromolecules 2008 Volume 41(Issue 20) pp:7469-7477
Publication Date(Web):October 2, 2008
DOI:10.1021/ma801213n
A fluorinated polyimide was employed to investigate reaction-induced phase separation of epoxy/polyimide blends. Three distinct morphological structures were obtained. Among these, an unusual three-layered structure was observed in a certain polyimide concentration range. The polyimide-rich phase was mainly localized in the middle layer and the outer layers were epoxy-rich. The thickness of the outer layers (10−30 μm) was much larger than the characteristic length of the bicontinuous domains in the middle layer. In the lower polyimide concentration range, polyimide-rich particles formed in the epoxy-rich matrix as aggregates without further coalescence. At higher polyimide concentrations, polyimide-rich phase formed continuous domains while epoxy-rich phase formed connected nonspherical particles. Evolution of the layered structure was elucidated from scanning electron micrographs. No layer existed in the sample before phase separation began. The reaction conversion of epoxy was very low when layers started to form. During that period, the outer layers thickened rapidly. The mechanism of this unusual layered structure formation was discussed based on the characteristics of this epoxy/polyimide system. Also a refractive index cross-over was observed which was caused by the gradual increase of the refractive index of epoxy during the isothermal curing process.
Co-reporter:Kai Du;Aihua H. He;Xin Liu
Macromolecular Rapid Communications 2007 Volume 28(Issue 24) pp:2294-2299
Publication Date(Web):2 NOV 2007
DOI:10.1002/marc.200700592
Highly exfoliated poly(propylene) (PP)/clay nanocomposites with obvious improvements in both the tensile strength and toughness have been prepared by a novel TiCl4/MgCl2/imidazolium-modified montmorillonite (IOHMMT) compound catalysts. Through this approach, in situ propylene polymerization can actually take place between the silicate layers and lead not only to PP with a high isotacticity and molecular weight, but also to a highly exfoliated structure even at high clay content levels (as high as 19 wt.-%).
Co-reporter:Jianfen Zheng;Aihua He;Junxing Li
Macromolecular Rapid Communications 2007 Volume 28(Issue 22) pp:
Publication Date(Web):8 OCT 2007
DOI:10.1002/marc.200700544
Polymorphism control of PVDF has been realized through electrospinning. PVDF fibrous membranes with fiber diameter in the range of 100 nm to several micrometers were produced by electrospinning and the crystal phase of electrospun PVDF fibers can be adjusted at the same time. Through the control of electrospinning parameters such as the solvent, electrospinning temperature, feeding rate, and tip-to-collector distance, PVDF fibrous membranes containing mainly α- or β- or γ-phase could be fabricated successfully.
Co-reporter:ChengGui Zhang;Xia Dong;DuJin Wang
Science Bulletin 2007 Volume 52( Issue 15) pp:2042-2047
Publication Date(Web):2007 August
DOI:10.1007/s11434-007-0291-0
In this paper, high density polyethylene (HDPE)/poly(ethylene-co-butene) (PEB) blend (50/50 wt%) was prepared through solution blending and then compression molding, and subsequently examined by laser scanning confocal microscopy (LSCM). The PEB used in this experiment was labeled with a small quantity of a fluorescein derivative to render fluorescence. The initial films showed uniform dye distribution and no indication of phase separation within the resolution of optical microscopy. Sample films annealing at 140°C followed by rapid cooling to room temperature showed obvious phase separation and bicontinuous structure. The present work indicates that by labeling one component with fluorescein derivative, LSCM can efficiently perform in situ depth profiling of polymer blends.
Co-reporter:Xia Dong;Xiaohua Zhang;Chenggui Zhang;Kun Meng
Macromolecular Rapid Communications 2006 Volume 27(Issue 19) pp:1677-1683
Publication Date(Web):27 SEP 2006
DOI:10.1002/marc.200600403
Summary: Shear-induced crystallization in a blend of isotactic poly(propylene) and poly(ethylene-co-octene) (iPP/PEOc) has been investigated by means of in-situ optical microscopy and a shear hot stage under various thermal and shear histories. Cylindrites are observed after shear in the phase-separated iPP/PEOc blends for the first time. The nuclei (shish) come from the orientation of the entangled network chains, and the relationship between the shear rate and the network relaxation time of the oriented iPP chains is a very important factor that dominates the formation of the cylindrites after liquid-liquid phase separation. The cylindrites can grow through phase-separated domains with proper shear rate and shear time. In addition, the number of spherulites increases with shear rate, which is consistent with the notion of fluctuation-induced nucleation/crystallization.
Co-reporter:Song Hong;Yonghua Yao;Hongli Ge;Xia Dong
Macromolecular Rapid Communications 2006 Volume 27(Issue 19) pp:1627-1631
Publication Date(Web):27 SEP 2006
DOI:10.1002/marc.200600415
Summary: With the proper selection of shear and thermal conditions, super-hydrophobic polymeric surfaces (contact angle > 150°) with tunable sliding angles (from less than 1° to higher than 90°) can be prepared from pure isotactic poly(propylene) (iPP) without any further modification with low-surface-energy components under ambient atmosphere. The formed surfaces have naturally good thermal properties, chemical and moisture resistance, low density, and potentially low manufacturing cost.
Co-reporter:Yonghua Yao;Song Hong;Hongli Ge;Xia Dong
Macromolecular Rapid Communications 2006 Volume 27(Issue 19) pp:
Publication Date(Web):13 OCT 2006
DOI:10.1002/marc.200690040
Co-reporter:Junxing Li;Aihua He;Benjamin S. Hsiao;Benjamin Chu;Dufei Fang
Macromolecular Rapid Communications 2006 Volume 27(Issue 2) pp:114-120
Publication Date(Web):29 DEC 2005
DOI:10.1002/marc.200500726
Summary: In the present study, electrospinning of hyaluronic acid (HA) and hyaluronic acid/gelatin (HA-GE) blends in N,N-dimethylformamide (DMF)/water-mixed solvents have been investigated. When the volume ratio of DMF to water was in the range of 1.5–0.5, HA solutions could be electrospun into fibrous membranes successfully. The average diameter of HA fibers was about 200 nm. The HA-GE composite nanofibrous membranes with varied HA/GE weight ratio in the range of 100/20–100/100 have also been successfully fabricated. The average diameter of HA-GE fibers was in the range of 190–500 nm. The decrease in surface tension could promote fiber formation. Thus, an introduction of DMF that could decrease the surface tension distinctively, without significant change or increase in viscosity of the solution, could bypass the use of blowing-assisted electrospinning. Our postulated picture is that the lower surface tension could help the ejection of stream with relatively high viscosity and reduce or prevent the droplet formation during the spinning process.
Co-reporter:Xiaohua Zhang;Zhigang Wang;Murugappan Muthukumar;Xiaohua Zhang;Zhigang Wang;Murugappan Muthukumar
Macromolecular Rapid Communications 2005 Volume 26(Issue 16) pp:1285-1288
Publication Date(Web):3 AUG 2005
DOI:10.1002/marc.200500304
Summary: The liquid-liquid phase separation (LLPS) is often coupled with other ordering processes such as crystallization. In a polyolefin blend system, overwhelming changes in crystallization kinetics due to concentration fluctuation caused by spontaneous spinodal LLPS have been observed. Consequently, we are proposing a new mechanism of “fluctuation-assisted crystallization”. In this process, the usual nucleation barrier could be overcome (or at least partially) by the spontaneous fluctuation growth of LLPS in the spinodal region.
Co-reporter:Haiqing Hu;Chenggui Zhang;Chuanbo Chong;Aihua He;Guoqiang Fan;Jin-Yong Dong;Haiqing Hu;Chuanbo Chong;Aihua He;Chenggui Zhang;Guoqiang Fan;Jin-Yong Dong
Macromolecular Rapid Communications 2005 Volume 26(Issue 12) pp:973-978
Publication Date(Web):9 JUN 2005
DOI:10.1002/marc.200500182
Summary: The phase behavior of poly(ethylene-co-styrene) (PES) and poly(ethylene-co-butene) (PEB) blends has been studied. A closed-loop phase diagram was clearly observed in this weakly interacting system as the styrene content in the PES decreased to about 1 mol-%. At higher styrene contents, the phase loop starts to interplay with the crystallization transformation at lower temperatures.
Co-reporter:Bo Shen ; Yongri Liang ; Chenggui Zhang
Macromolecules () pp:
Publication Date(Web):August 17, 2011
DOI:10.1021/ma200559f
When a shear-induced crystallization of polymers was formed between a pair of rotating plates, there existed two possibilities in forming this shear-induced crystal: one is that the shish-kebab formed is uniformly distributed in the bulk polymer melt, and the other is that it appears only on both sides of polymer–substrate interfaces. Since the mechanism of each scenario depends on the boundary conditions of the experiment, we mainly focus on the second scenario in this study and will discuss why and when the shish-kebab grows on the polymer–substrate interfaces. Through the ex-situ polarized optical images of flow–velocity gradient plane, velocity gradient–vorticity plane, and flow–vorticity plane combined with in situ phase contrast optical images and attenuated total reflection (ATR) Fourier transformed infrared spectrum, we are able to infer how shish-kebab is distributed in the bulk. We conjectured that wall slip might be the most possible and reasonable origin for the formation of the shish-kebab on the interface which leads to the two different scenarios mentioned above. This is confirmed by the results from the shear rate dependence experiment. Shear time dependence experiment is also made to study the long shear time effect. By carefully cleaning the quartz plate used for shear experiment and comparing with the results obtained from uncleaned quartz plate, we further testified our point of view and led to some physical understanding for the formation of the shish-kebab as well as the wall slip mechanism.
