Co-reporter:Chunyu Li, Rui Liu, Qingbin Xue, Yaping Huang, Yunlan Su, Qiang Shen, and Dujin Wang
Langmuir November 14, 2017 Volume 33(Issue 45) pp:13060-13060
Publication Date(Web):October 24, 2017
DOI:10.1021/acs.langmuir.7b02596
A molecular solution of an amphiphilic block copolymer may act as an oil phase by dispersing into an aqueous micellar system of small-molecular surfactant, forming oil-in-water (O/W) emulsion droplets. In this paper, an as-synthesized triblock copolymer poly(l-lactide)–polyoxyethylene–poly(l-lactide) (PLLA–PEO–PLLA) was dissolved in tetrahydrofuran (THF) and then added to an aqueous micellar solution of nonaethylene glycol monododecyl ether (AEO-9), forming initially coalescent O/W emulsion droplets in the size range of 35 nm–1.3 μm. Along with gradual volatilization of THF and simultaneous concentration of PLLA–PEO–PLLA molecules, the amphiphilic copolymer backbones themselves experience solution-based self-assembly, forming inverted core–corona aggregates within an oil-phase domain. Anisotropic coalescence of adjacent O/W emulsion droplets occurs, accompanied by further volatilization of THF. The hydrophilic block crystallization of core-forming PEOs and the hydrophobic chain stretch of corona-forming PLLAs together induce the intermediate formation of rod-like architectures with an average diameter of 300–800 nm, and this leads to a large-scale deposition of the triblock copolymer fibers with an average diameter of ∼2.0 μm. Consequently, this strategy could be of general interest in the self-assembly formation of amphiphilic block copolymer fibers and could also provide access to aqueous solution crystallization of hydrophilic segments of these copolymers.
Co-reporter:Xiao Kuang;Guoming Liu;Xia Dong;Dujin Wang
Materials Chemistry Frontiers 2017 vol. 1(Issue 1) pp:111-118
Publication Date(Web):2016/11/30
DOI:10.1039/C6QM00094K
Smart polymers based on covalent adaptive networks (CANs) with reversible covalent bonds have drawn tremendous attention in the past few years. The relaxation properties of CANs polymers play an important role because of their stimuli-responsive capability. Here, we elucidate the correlation between the stress relaxation dynamics and reaction thermochemistry of CANs polymers. Diels–Alder (DA) reaction based cross-linked elastomers are utilized as model CANs polymers. In situ FTIR data reveals the dynamic reaction kinetics and thermodynamics in the solid state. The influence of cross-linking density on the temperature-dependent stress relaxation time of the CANs polymers well above the gel point can be normalized by the relative distance to the gel point conversion. Combining the Semenov–Rubinstein theory and Arrhenius' law, a simple scaling relationship between normalized relaxation time and reaction kinetics is established for CANs polymers.
Co-reporter:Weiwei Zhao;Yunlan Su;Xia Gao;Qingyun Qian;Xin Chen;Robert Wittenbrink;Dujin Wang
Journal of Polymer Science Part B: Polymer Physics 2017 Volume 55(Issue 6) pp:498-505
Publication Date(Web):2017/03/15
DOI:10.1002/polb.24291
ABSTRACTThe confinement effects introduced by nanoparticles have been reported to influence the phase behaviors thus the properties of polymer nanocomposites. In this study, molecular dynamics and crystallization behaviors of polyethylene (PE) composited with three types of silica (SiO2) nanoparticles, namely unmodified SiO2, hydrophobically modified SiO2, SiO2-APTES (3-aminopropyltriethoxysilane) and SiO2-PTES (n-propyltriethoxysilane), were systematically investigated via a combination of DSC, XRD and 1H solid-state NMR measurements. The suppressions in crystallization and chain mobilities of PE rank in the order of unmodified SiO2 < SiO2-APTES < SiO2-PTES due to the increasing interfacial interactions between PE and SiO2 nanoparticles. Additionally, independent of polymer–nanoparticle interactions, a silica network forms for all three kinds of nanocomposites when SiO2 content reaches 83 wt %. The mobilities of polymer chains are severely restricted by such a percolated network structure, leading to a turning point in the crystallization ability of nanocomposites and a new crystallization peak at 45 °C lower than that of pure PE. The synergetic effects of interfacial interactions and filler network on polymer crystallization have been thoroughly studied in this work, which will provide guidance on modifying and designing nanocomposites with controlled properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 498–505
Co-reporter:
Journal of Polymer Science Part B: Polymer Physics 2017 Volume 55(Issue 5) pp:418-424
Publication Date(Web):2017/03/01
DOI:10.1002/polb.24293
ABSTRACTCompared with the most stable crystalline form of isotactic polypropylene (α-iPP), β-iPP shows superior impact strength and high temperature performance, though the mechanism of how the frustrated structure of β-iPP is formed still remains unclear. In present work, the single crystal structure of a traditional β-iPP nucleating agent, N,N′-dicyclohexylterephthalamide (DCHT), was obtained for the first time and correlated with the epitaxial crystallization of β-iPP on the surface of DCHT crystal. The combination of synchrotron radiation X-ray microdiffraction and molecular chain packing model confirmed that a two dimensional match of chain-axis and inter-chain direction coexists between β-iPP (110) plane and DCHT (001) plane. It was further found that an epitaxial model is helpful to understand the formation of the frustrated structure of 31 helices packing in β-iPP. The molecular mechanics computation showed that as the (001) plane of DCHT is fixed, the packing mode of β-iPP (110) plane on the substrate surface is more stable than that of α-iPP (010) plane. This work clarifies the epitaxial crystallization mechanism of β-iPP on DCHT by employing both experimental and computational evidences. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 418–424
Co-reporter:Xiao Kuang;Guoming Liu;Xia Dong ;Dujin Wang
Macromolecular Materials and Engineering 2016 Volume 301( Issue 5) pp:535-541
Publication Date(Web):
DOI:10.1002/mame.201500425
Co-reporter:Weiwei Zhao;Yunlan Su;Xia Gao;Jianjun Xu;Dujin Wang
Journal of Polymer Science Part B: Polymer Physics 2016 Volume 54( Issue 3) pp:414-423
Publication Date(Web):
DOI:10.1002/polb.23915
ABSTRACT
The impact of nanoconfinement introduced by nanoparticles on polymer crystallization has attracted extensive attention because it plays an important role in the ultimate properties of polymer nanocomposites. In this study, interfacial and spatial confinement effects of silica (SiO2) nanoparticles on the crystallization behaviors of poly(ethylene oxide) (PEO)/SiO2 composites were systematically investigated by changing the size and concentration of SiO2 in PEO matrix. The composites with high silica loadings exhibit two crystallization peaks of PEO as determined by differential scanning calorimetry. The first peak at 7–43 °C is related to the bulk PEO, while the second peak at −20 to −30 °C is attributed to the restricted PEO segments. Three-layer (amorphous, interfacial, and bulk) model is proposed to interpret the confined crystallization of PEO/SiO2 composites, which is supported by the results of thermogravimetric analysis and solid-state 1H nuclear magnetic resonance. In amorphous layer, most PEO segments are directly adsorbed on SiO2 surface via hydrogen bonding. The interfacial PEO layer, which is nonuniform, is composed of crystallizable loops and tails extending from amorphous layer. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 414–423
Co-reporter:Xia Gao, Patrick Huber, Yunlan Su, Weiwei Zhao, and Dujin Wang
The Journal of Physical Chemistry B 2016 Volume 120(Issue 30) pp:7522-7528
Publication Date(Web):July 7, 2016
DOI:10.1021/acs.jpcb.6b00119
The crystallization behavior of an archetypical soft/hard hybrid nanocomposite, that is, an n-octadecane C18/SiO2-nanoparticle composite, was investigated by a combination of differential scanning calorimetry (DSC) and variable-temperature solid-state 13C nuclear magnetic resonance (VT solid-state 13C NMR) as a function of silica nanoparticles loading. Two latent heat peaks prior to bulk freezing, observed for composites with high silica loading, indicate that a sizable fraction of C18 molecules involve two phase transitions unknown from the bulk C18. Combined with the NMR measurements as well as experiments on alkanes and alkanols at planar amorphous silica surfaces reported in the literature, this phase behavior can be attributed to a transition toward a 2D liquid-like monolayer and subsequently a disorder-to-order transition upon cooling. The second transition results in the formation of a interface-frozen monolayer of alkane molecules with their molecular long axis parallel to the nanoparticles’ surface normal. Upon heating, the inverse phase sequence was observed, however, with a sizable thermal hysteresis in accord with the characteristics of the first-order phase transition. A thermodynamic model considering a balance of interfacial bonding, chain stretching elasticity, and entropic effects quantitatively accounts for the observed behavior. Complementary synchrotron-based wide-angle X-ray diffraction (WAXD) experiments allow us to document the strong influence of this peculiar interfacial freezing behavior on the surrounding alkane melts and in particular the nucleation of a rotator phase absent in the bulk C18.
Co-reporter:Deqing Zhang;Dujin Wang
Science China Chemistry 2016 Volume 59( Issue 10) pp:1229-1230
Publication Date(Web):2016 October
DOI:10.1007/s11426-016-0352-0
Co-reporter:Jian Yang, Haijin Zhu, Chunbo Zhang, Qianhong Jiang, Ying Zhao, Peng Chen, Dujin Wang
Polymer 2016 Volume 83() pp:230-238
Publication Date(Web):28 January 2016
DOI:10.1016/j.polymer.2015.12.025
•A green and industrially viable process was demonstrated for toughening PLLA/PHBV bio-alloy.•The biocompatible and biodegradable nature of bio-alloy is not compromised with addition of zinc acetate.•The miscibility and mechanical properties of PLLA/PHBV bio-alloy were improved prominently.•A new mechanism of transesterification accompanied by decomposition competition was proposed.In order to improve the miscibility and mechanical properties of poly(l-lactic acid) (PLLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) bio-alloy, small amount of transesterification catalyst, zinc acetate was added in the melt blending process. We show that the PLLA-PHBV copolymer generated during the melt blending significantly improves the miscibility and therefore enhances the mechanical properties of the product. Dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), and tensile tests were performed to study the miscibility and mechanical properties of the blends. Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC) were used to reveal the molecular structural, and molecular weight changes of PLLA and PHBV after melt mixing with zinc acetate. SEM and FTIR results have clearly shown that the PLLA-PHBV copolymer generated from transesterification reaction acted as a compatibilizer and therefore resulted in an improved interfacial miscibility and ductility of PLLA/PHBV blend. In our mechanistic study, a competition between the PLLA/PHBV transesterification reaction and the thermal decomposition of PHBV was identified for the first time. On the basis of these observations, a new mechanism of transesterification reaction was proposed.
Co-reporter:Xiao Kuang, Guoming Liu, Xia Dong, Dujin Wang
Polymer 2016 Volume 84() pp:1-9
Publication Date(Web):10 February 2016
DOI:10.1016/j.polymer.2015.12.033
In this work, we report a novel tripe-shape memory (TSM) strategy using glass transition and thermally reversible Diels–Alder (DA) reaction as two distinct switch units in a network. Based on this principle, a series of TSM epoxy materials were facilely prepared through the reaction of a conventional epoxy oligomer, an aliphatic diamine and a diamine DA adduct cross-linker via a one-pot approach. The thermal and thermal dynamic properties of the reversible–irreversible dual cross-linking epoxy network were studied by differential scanning calorimetry (DSC) analysis and dynamic mechanical thermal analysis (DMTA), respectively. The thermal reversibility of DA adduct was revealed by Fourier transform infrared spectroscopy (FTIR). The TSM effect of the epoxy materials was demonstrated and quantitatively studied by DMTA. The development of thermal-responsive DA adduct as a molecular switch provides a new insight into the design and functionalization of multi-shape memory polymers.
Co-reporter:Qianhong Jiang, Ying Zhao, Chunbo Zhang, Jian Yang, Yizhuang Xu, Dujin Wang
Polymer 2016 Volume 105() pp:133-143
Publication Date(Web):22 November 2016
DOI:10.1016/j.polymer.2016.10.004
•Microstructural variation of mesomorphic iPP in the heating process was revealed.•Microstructural change in the temperature range from 20 and 60 °C was detected.•Plausible structural evolution mechanism in the meso-α transformation was proposed.The microstructural changes of mesomorphic iPP from mesophase to α transition at a molecular level in a continuous heating process have been studied by in-situ Fourier-transform infrared (FT-IR) spectroscopy, in-situ X-ray scattering using synchrotron radiation, differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Microstructural change corresponding to helical conformation variation in the temperature range between 20 and 60 °C was detected by IR spectroscopy, which may originate from the glass transition of rigid amorphous fraction (RAF). The helical sequence with 12 monomer units is found to exist in RAF. The contents of helical sequences with different number of monomers exhibit different variation trends in the course of meso-α transition and the following process of partial melting and perfection of α crystal. A plausible mechanism was proposed that RAF experiences glass transition firstly at low temperature, and then serve as α nuclei to trigger the meso-α transition at higher temperature. This work provides a new insight into the mechanism of microstructural evolution of the meso-α transformation of iPP.
Co-reporter:Haiming Chen, Guoming Liu, Yunpeng Qin, Alejandro J. Müller, Jianhui Hou, and Dujin Wang
Macromolecules 2016 Volume 49(Issue 22) pp:8653-8660
Publication Date(Web):November 10, 2016
DOI:10.1021/acs.macromol.6b02218
The structural transitions in solution-cast film of poly[5,5′-bis(2-butyloctyl)-(2,2′-bithiophene)-4,4′-dicarboxylate-alt-5,5′-2,2′-bithiophene] (PDCBT) copolymer have been systematically studied by a combination of differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), in situ Fourier transform infrared spectroscopy (FTIR), UV–vis spectroscopy, and in situ wide-angle X-ray scattering (WAXS). The glass transition temperature of the main chain as well as the melting and crystallization temperatures of the polymer were determined as 10, 238, and 221 °C, respectively. The out-of-plane deformation vibration of PDCBT Cβ–H groups in FTIR has been manifestly assigned for the first time. A broad endothermic peak between 30 and 120 °C was observed during DSC heating process and was attributed to the enthalpic relaxation of the twist glass transition, which resulted in a small negative effect on the power conversion efficiency (PCE) of solar cells. A reorganization process in the crystalline region was observed in WAXS upon heating, including the increase of grain size along the a-axis.
Co-reporter:Zhiyong Li, Yunlan Su, Baoquan Xie, Xianggui Liu, Xia Gao and Dujin Wang
Journal of Materials Chemistry A 2015 vol. 3(Issue 9) pp:1769-1778
Publication Date(Web):13 Jan 2015
DOI:10.1039/C4TB01653J
A novel physically linked double-network (DN) hydrogel based on natural polymer konjac glucomannan (KGM) and synthetic polymer polyacrylamide (PAAm) has been successfully developed. Polyvinyl alcohol (PVA) was used as a macro-crosslinker to prepare the PVA–KGM first network hydrogel by a cycle freezing and thawing method for the first time. Subsequent introduction of a secondary PAAm network resulted in super-tough DN hydrogels. The resulting PVA–KGM/PAAm DN hydrogels exhibited unique ability to be freely shaped, cell adhesion properties and excellent mechanical properties, which do not fracture upon loading up to 65 MPa and a strain above 0.98. The mechanical strength and microstructure of the DN hydrogels were investigated as functions of acrylamide (AAm) content and freezing and thawing times. A unique embedded micro-network structure was observed in the PVA–KGM/PAAm DN gels and accounted for the significant improvement in toughness. The fracture mechanism is discussed based on the yielding behaviour of these physically linked hydrogels.
Co-reporter:Guoming Liu;Xiuqin Zhang;Dujin Wang
Polymer International 2015 Volume 64( Issue 8) pp:951-956
Publication Date(Web):
DOI:10.1002/pi.4903
Abstract
This minireview introduces the state of the art in the stress induced reversible crystal transition phenomenon frequently found in polyethers and polyesters. This type of crystal transition is thermodynamically a first order phase transition. Microscopically, it generally corresponds to a change from gauche conformers to trans conformers under external stress, which leads to longer repeating length per monomeric unit along polymer chains. The dimension of the lamellar structure is influenced by the crystal transition as well. The crystal lattice parameters, chain conformation, critical stress and the energy barrier for crystal transition in different polymers are summarized. The mechanical property features imparted by the reversible crystal transition are briefly introduced. © 2015 Society of Chemical Industry
Co-reporter:Tao Wen;Xiuqin Zhang;Zujiang Xiong;Sicco de Vos;Ruyin Wang;Fosong Wang;Dujin Wang
Journal of Applied Polymer Science 2015 Volume 132( Issue 2) pp:
Publication Date(Web):
DOI:10.1002/app.41273
ABSTRACT
In the present work, the fracture behavior of transcrystallization (TC) of poly(l-lactic acid) (PLLA) in thin film and the dependence of mechanical properties on the morphology of TC have been studied. The nucleation density of TC was merely determined by the annealing temperatures of the fibers which used for inducing nucleation, and the crystallization temperature and time of the samples were completely identical. By using in situ polarized optical microscopy, the fracture process of TCs was characterized. For the TC with high nucleating density (TC-H), lots of cracks were generated from the TC bulk during fracture. But only few cracks were observed on the TC with low nucleation density (TC-L), and the final fracture of TC-L always occurred in the junctions of crystal segments. Compared to the samples which do not contain TC, the fracture strength was enhanced by 8.1% because of the presence of TC-H. On the contrary, the presence of TC-L can reduce the fracture strength of the samples. The fracture surfaces of TC were characterized by scanning electron microscope. It was observed that the fracture surface of TC-H exhibited obvious fibrillation and cavitation, but the fracture surface of TC-L was smooth and featureless. The possible fracture mechanism for two TCs was discussed in view of their intrinsic crystal organizations. © 2014 The Authors Journal of Applied Polymer Science Published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41273.
Co-reporter:Xiao Kuang;Guoming Liu;Xia Dong;Xianggui Liu;Jianjun Xu;Dujin Wang
Journal of Polymer Science Part A: Polymer Chemistry 2015 Volume 53( Issue 18) pp:2094-2103
Publication Date(Web):
DOI:10.1002/pola.27655
ABSTRACT
A reversibly cross-linked epoxy resin with efficient reprocessing and intrinsic self-healing was prepared from a diamine Diels-Alder (DA) adduct cross-linker and a commercial epoxy oligomer. The newly synthesized diamine cross-linker, comprising a DA adduct of furan and maleimide moieties, can cure epoxy monomer/oligomer with thermal reversibility. The reversible transition between cross-linked state and linear architecture endows the cured epoxy with rapid recyclability and repeated healability. The reversibly cross-linked epoxy fundamentally behaves as typical thermosets at ambient conditions yet can be fast reprocessed at elevated temperature like thermoplastics. As a potential reversible adhesive, the epoxy polymer with adhesive strength values about 3 MPa showed full recovery after repeated fracture-thermal healing processes. The methodology explored in this contribution provides new insights in modification of conventional engineering plastics as functional materials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2094–2103
Co-reporter:Xiao Kuang, Guoming Liu, Liuchun Zheng, Chuncheng Li, Dujin Wang
Polymer 2015 Volume 65() pp:202-209
Publication Date(Web):18 May 2015
DOI:10.1016/j.polymer.2015.03.074
•Unsaturated biodegradable poly(butylene fumarate) was functionalized by Michael addition.•Fast reversibly cross-linked polyester was prepared by Diels–Alder reaction.•Competition between cross-linking reaction and crystallization was controlled by thermal treatment.•Mechanical properties were widely tunable from elastomer to plastic.A novel strategy for preparation of unsaturated polyester-based functional materials with widely tunable mechanical properties has been reported in present work. The biodegradable and crystallizable poly(butylene fumarate) oligomer (PBF) bearing reactive carbon–carbon double bonds on the backbone was functionalized by Michael addition with furfurylamine (FA), followed by incorporating bismaleimide (BMI) as cross-linker to form a reversibly cross-linked polyester (PBF-FA-BMI). The obtained material was systematically characterized by a combination of differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), rheometry measurement, wide-angle X-ray scattering (WAXS) as well as mechanical property testing. The in-situ FTIR and rheology measurements demonstrated the competition process of DA reaction and crystallization for dynamic conditions and isothermal conditions. The characteristic of dynamically chemical structure variation and crystallization behavior provides a possibility to tune the mechanical property of PBF-FA-BMI. By thermal treatment, the structure programming of the material can be facilely achieved, which undergoes from a typically elastomer to plastic. A schematic illustration of thermo-responsive conversion and recyclability is proposed for the cross-linked polyester.Figure optionsDownload full-size imageDownload as PowerPoint slide
Co-reporter:Xia Gao, Baoquan Xie, Yunlan Su, Dongsheng Fu, and Dujin Wang
The Journal of Physical Chemistry B 2015 Volume 119(Issue 5) pp:2074-2080
Publication Date(Web):January 12, 2015
DOI:10.1021/jp512124s
Motivated by the interest in an interfacial effect on crystallization behaviors and material properties of polymer nanocomposites, phase behaviors of a novel model system for polymer nanocomposite, 1-octadecanol/silica nanosphere composites (C18OH/SiO2), were studied by means of thermal analysis and wide-angle X-ray diffraction. Although a huge specific surface area of silica nanoparticles enlarges the surface–volume ratio of C18OH molecules, surface freezing phenomenon is not observed by DSC in the C18OH/SiO2 composites. While pure C18OH exhibits rotator RIV phase with molecules tilted with respect to the layer normal, the silica network favors and enhances untitled RII phase by disturbing the layering arrangement. Moreover, the confined C18OH shows a polycrystalline mixture of orthorhombic β form and monoclinic γ form. It is demonstrated that the interfacial interaction between the C18OH molecules and the silica surface contributes to the peculiar phase transition behaviors of C18OH/SiO2 composites. The investigation of the model system of long-chain alcohol/nano-SiO2 composites may help us to understand the complicated interfacial effect on phase behaviors and material properties of polymer nanocomposite systems.
Co-reporter:Yu Guan, Guoming Liu, Guqiao Ding, Tieying Yang, Alejandro J. Müller, and Dujin Wang
Macromolecules 2015 Volume 48(Issue 8) pp:2526-2533
Publication Date(Web):April 15, 2015
DOI:10.1021/acs.macromol.5b00108
The crystallization behavior of poly(l-lactic acid) (PLLA) infiltrated in anodic alumina oxide templates (AAO) was investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). During heating from the glassy state, the crystallization of infiltrated PLLA was unexpectedly enhanced as compared with bulk PLLA. The cold crystallization temperature of infiltrated PLLA from the glassy state was much lower than that of bulk PLLA. The half-crystallization time (t1/2) of infiltrated PLLA at 75 °C decreased with the diameter of AAO nanopores. The glass transition temperature of PLLA was not influenced by the geometrical confinement. The enhanced crystallization from the glassy state was explained by surface-induced nucleation of AAO walls on PLLA. Our results provide the first observation of enhanced cold crystallization of polymers in confined geometry.
Co-reporter:Yunlan Su, Guoming Liu, Baoquan Xie, Dongsheng Fu, and Dujin Wang
Accounts of Chemical Research 2014 Volume 47(Issue 1) pp:192
Publication Date(Web):August 15, 2013
DOI:10.1021/ar400116c
How polymers crystallize can greatly affect their thermal and mechanical properties, which influence the practical applications of these materials. Polymeric materials, such as block copolymers, graft polymers, and polymer blends, have complex molecular structures. Due to the multiple hierarchical structures and different size domains in polymer systems, confined hard environments for polymer crystallization exist widely in these materials. The confined geometry is closely related to both the phase metastability and lifetime of polymer. This affects the phase miscibility, microphase separation, and crystallization behaviors and determines both the performance of polymer materials and how easily these materials can be processed. Furthermore, the size effect of metastable states needs to be clarified in polymers. However, scientists find it difficult to propose a quantitative formula to describe the transition dynamics of metastable states in these complex systems. Normal alkanes [CnH2n+2, n-alkanes], especially linear saturated hydrocarbons, can provide a well-defined model system for studying the complex crystallization behaviors of polymer materials, surfactants, and lipids. Therefore, a deeper investigation of normal alkane phase behavior in confinement will help scientists to understand the crystalline phase transition and ultimate properties of many polymeric materials, especially polyolefins.In this Account, we provide an in-depth look at the research concerning the confined crystallization behavior of n-alkanes and binary mixtures in microcapsules by our laboratory and others. Since 2006, our group has developed a technique for synthesizing nearly monodispersed n-alkane containing microcapsules with controllable size and surface porous morphology. We applied an in situ polymerization method, using melamine–formaldehyde resin as shell material and nonionic surfactants as emulsifiers. The solid shell of microcapsules can provide a stable three-dimensional (3-D) confining environment. We have studied multiple parameters of these microencapsulated n-alkanes, including surface freezing, metastability of the rotator phase, and the phase separation behaviors of n-alkane mixtures using differential scanning calorimetry (DSC), temperature-dependent X-ray diffraction (XRD), and variable-temperature solid-state nuclear magnetic resonance (NMR). Our investigations revealed new direct evidence for the existence of surface freezing in microencapsulated n-alkanes. By examining the differences among chain packing and nucleation kinetics between bulk alkane solid solutions and their microencapsulated counterparts, we also discovered a mechanism responsible for the formation of a new metastable bulk phase. In addition, we found that confinement suppresses lamellar ordering and longitudinal diffusion, which play an important role in stabilizing the binary n-alkane solid solution in microcapsules. Our work also provided new insights into the phase separation of other mixed system, such as waxes, lipids, and polymer blends in confined geometry. These works provide a profound understanding of the relationship between molecular structure and material properties in the context of crystallization and therefore advance our ability to improve applications incorporating polymeric and molecular materials.
Co-reporter:Guoming Liu;Xiuqin Zhang;Dujin Wang
Advanced Materials 2014 Volume 26( Issue 40) pp:6905-6911
Publication Date(Web):
DOI:10.1002/adma.201305413
Poly(lactic acid) (PLA) is one of the most promising alternatives for petrochemical-based plastics. Crystallization mediation provides the simplest and most practical approach for enhancing the properties of PLA. Here, recent advances in understanding the relationship between crystalline structure and properties of PLA are summarized. Methods for manipulating crystallization towards high-performance PLA materials are introduced.
Co-reporter:Zhiyong Li, Tao Wen, Yunlan Su, Xiaoxiao Wei, Changcheng He and Dujin Wang
CrystEngComm 2014 vol. 16(Issue 20) pp:4202-4209
Publication Date(Web):17 Feb 2014
DOI:10.1039/C3CE42517G
Hydroxyapatite [HAp, Ca10 (PO4)6 (OH)2] crystals were successfully prepared by the electrophoresis approach and an ion diffusion method using a template of polyacrylamide (PAAm) hydrogel. Flower-like porous hollow HAp spheres were both obtained in the PAAm hydrogel by the two methods. The diameters of the HAp spheres could be controlled in the range of 500 nm to 28 μm. The formation of flower-like porous hollow HAp crystals is believed to be the combined result of the three-dimensional hydrogel template and electrostatic interaction.
Co-reporter:Guoming Liu, Konrad Schneider, Liuchun Zheng, Xiuqin Zhang, Chuncheng Li, Manfred Stamm, Dujin Wang
Polymer 2014 Volume 55(Issue 10) pp:2588-2596
Publication Date(Web):13 May 2014
DOI:10.1016/j.polymer.2014.03.055
The structure evolution of poly(vinylidene fluoride)/poly(butylene succinate) (PVDF/PBS) blends during stretching above the melting point of PBS is investigated by synchrotron-based simultaneous wide angle and small angle X-ray scattering (WAXS/SAXS). Before stretching, PVDF crystallizes into the α-form, whereas the chains of molten PBS locate at the inter-lamellar amorphous phase of PVDF. Crystal transition from α to β of PVDF is observed in all samples during stretching. The morphological transformation from a lamellar structure into a fibrillar structure occurs at low and intermediate strains. With further deformation, a “stretching induced phase separation” phenomenon is observed. The final microstructure of PVDF/PBS blends contains PVDF microfibrils with PBS chains preferentially distributed in the inter-fibrillar region. The PBS molecular weight influences the onset and end strain for the transition. A new “two-step model” is proposed to describe the deformation process.
Co-reporter:Guoming Liu, Liuchun Zheng, Xiuqin Zhang, Chuncheng Li, and Dujin Wang
Macromolecules 2014 Volume 47(Issue 21) pp:7533-7539
Publication Date(Web):October 23, 2014
DOI:10.1021/ma501832z
Multiblock copolymers consisting of crystalline poly(butylene succinate) and amorphous poly(1,2-propylene succinate) (PBS-co-PPS) are synthesized. The microstructure of the materials is investigated by the combination of thermal analysis and wide-angle/small-angle X-ray scattering (WAXS/SAXS). The noncrystalline PPS blocks are found to locate predominately in the amorphous phase between crystalline lamellae of PBS. By means of in situ WAXS coupled with optical-assisted strain measurement, the deformation process of PBS-co-PPS is studied. The stiffness and strength of PBS-co-PPS decrease with increasing PPS fraction, while the strain recovery behavior of PBS-co-PPS is similar to PBS homopolymer. Transition from α crystal to β crystal is observed for all the PBS-co-PPS samples. The critical stress for α–β transition of PBS-co-PPS is determined, which is found to be independent of PPS blocks. The universal critical stress for crystal transition is interpreted through a single-microfibril-stretching mechanism.
Co-reporter:Haifeng Shi, Ying Zhao, Xia Dong, Yong Zhou and Dujin Wang
Chemical Society Reviews 2013 vol. 42(Issue 5) pp:2075-2099
Publication Date(Web):17 Dec 2012
DOI:10.1039/C2CS35350D
Comb-like polymers with flexible side chains chemically pended onto a polymeric backbone afford some unusual properties due to their hierarchical structures, such as nanoscale confined crystallisation, phase transition and conformational variations, length scale effects, etc. Considerable attention has been paid to these featured polymers, regarding their importance in understanding the correlation between hierarchical structure and the assembled morphologies. In this review, we reviewed the recent research progress on the structure–property correlations of comb-like polymers. This article brings together and highlights the fabrication, structure determination and morphology characterization for comb-like polymers, especially for nanostructured packing patterns and frustrated mobility of chain segments from the selected examples.
Co-reporter:Yu Guan, Guoming Liu, Peiyuan Gao, Li Li, Guqiao Ding, and Dujin Wang
ACS Macro Letters 2013 Volume 2(Issue 3) pp:181
Publication Date(Web):February 14, 2013
DOI:10.1021/mz300592v
The confined crystallization behavior of a low molecular weight monodisperse polyethylene oxide (PEO) in anodic alumina oxide (AAO) templates was investigated. Homogeneous nucleation of polymer in AAO templates was confirmed. Within AAO with diameter larger than the contour length of PEO chains, the “kinetics selective growth” crystallization mechanism was confirmed based on the observation that the chain axis preferentially aligned perpendicular to the pore axis. However, when AAO diameter further decreases to a value smaller than the contour length of PEO, unique orientation with chain axis aligned parallel to the pore axis was observed for the first time. The results were discussed based on the competition between thermodynamics and kinetics during the crystallization process.
Co-reporter:Xiaoxiao Wei, Yunlan Su, Tao Wen, Zhiyong Li, Jian Yang and Dujin Wang
CrystEngComm 2013 vol. 15(Issue 17) pp:3417-3422
Publication Date(Web):19 Feb 2013
DOI:10.1039/C3CE26628A
Calcite rhombohedron with stepped indentation on its (104) face attached onto the air–solution interface was easily fabricated by using a non-ionic peptide type block copolymer poly (ethylene glycol)-b-poly (L-leucine) as the structure-directing agent. The balance of gravity and pulling force coming from the surface tension of the solution in combination with the limited Ca2+ and CO32− ion transport from the mineralization solution together played a significant role in modifying the crystal morphologies. Based on the calcite particle morphologies at different aging times, the mechanism for the formation of stepped calcite in the presence of polymer was proposed. This study provides an example that it is possible to access morphogenesis of calcium carbonate by a non-ionic copolymer which may shed new light on the controlled morphogenesis of other inorganic materials.
Co-reporter:Zujiang Xiong, Guoming Liu, Xiuqin Zhang, Tao Wen, Sicco de Vos, Cornelis Joziasse, Dujin Wang
Polymer 2013 Volume 54(Issue 2) pp:964-971
Publication Date(Web):24 January 2013
DOI:10.1016/j.polymer.2012.11.076
Formation of stereocomplex crystals (sc-crystals) of poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) blend has been recognized as a unique opportunity to dramatically improve the heat-resistant of poly(lactic acid) (PLA). In this study, we investigated the dynamic formation and transition of sc-crystals in PLLA/PDLA drawn film with a combination of in-situ synchrotron wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC). The correlation between sc-crystals content and the competing formation of α crystals (stable phase of PLA) in homopolymers during continuous heating and cooling processes was also studied. It was found that at room temperature, the original PLLA/PDLA drawn film consisted of only α crystals, however, with temperature increasing, two populations of sc-crystals were formed at different temperatures from the oriented amorphous region and the molten α crystals in the highly-oriented sample, respectively. Furthermore, new types of sc-crystals and α crystals with the orientation perpendicular to the original sc-crystals were formed during subsequent cooling process. On the basis of the X-ray scattering and DSC data, a schematic model for crystallization and oriented variation concerning sc-crystals and α crystals was proposed.
Co-reporter:Fa-liang Luo 罗发亮;Fa-hai Luo;Qian Xing
Chinese Journal of Polymer Science 2013 Volume 31( Issue 12) pp:1685-1696
Publication Date(Web):2013 December
DOI:10.1007/s10118-013-1364-y
In the present work, the blend of poly(butylene succinate) (PBS) and bisphenol A (BPA) was prepared by solution mixing, and the intermolecular interactions between the two components were characterized by a combination of nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The results showed that intermolecular hydrogen-bonding forms between the carbonyl group of PBS and phenol hydroxyl of BPA. With the increase of BPA content, more hydrogen bonds were formed. The effect of hydrogen bonding on the crystallization behavior of PBS was investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The results showed that the overall isothermal crystallization kinetics and the spherulite growth rate of PBS decrease with the increase of BPA content, while the PBS spherulite size increases with BPA content.
Co-reporter:Xia Gao, Dongsheng Fu, Yunlan Su, Yong Zhou, and Dujin Wang
The Journal of Physical Chemistry B 2013 Volume 117(Issue 44) pp:13914-13921
Publication Date(Web):September 27, 2013
DOI:10.1021/jp406896n
The phase behaviors of binary consecutive even normal alkane (n-alkane) mixtures (n-CnH2n+2/n-Cn+2H2n+6, with mass ratios of 90/10 and 10/90) with different average carbon numbers n̅ both in the bulk state (abbreviated as Cn/Cn+2) and in nearly monodisperse microcapsules (abbreviated as m-Cn/Cn+2), have been investigated by the combination of differential scanning calorimetry and temperature-dependent X-ray diffraction. The phase behavior of n-alkane mixtures gradually shifts from complete phase separation, partial miscibility to total miscibility in both bulk and microcapsules with the increase of average carbon numbers n̅. There are critical points for average carbon numbers of Cn/Cn+2, where the corresponding mixtures exhibit coexistence of a triclinic phase (formed by alkane with a longer chain) and an orthorhombic ordered phase (formed by the two components of mixtures). Due to the confinement from hard shells of microcapsules, the critical points of m-Cn/Cn+2 are smaller than those of Cn/Cn+2. Such a phase behavior originates from the delicate combined action of confinement and repulsion energy for the encapsulated n-alkane mixtures with different average carbon numbers n̅. When n̅ is less than the critical point, the repulsion energy between the two kinds of molecules exceeds the suppression effect of confinement, and phase separation occurs in microcapsules. It is believed that the average carbon number is another important factor that exerts strong negative influence on the phase separation of m-Cn/Cn+2 systems.
Co-reporter:Dongsheng Fu, Yunlan Su, Xia Gao, Yufeng Liu, and Dujin Wang
The Journal of Physical Chemistry B 2013 Volume 117(Issue 20) pp:6323-6329
Publication Date(Web):April 25, 2013
DOI:10.1021/jp4021849
Crystallization and phase transition behaviors of n-hexadecane (n-C16H34, abbreviated as C16) confined in microcapsules and n-alkane/SiO2 nanosphere composites have been investigated by the combination of differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). As evident from the DSC measurement, the surface freezing phenomenon of C16 is enhanced in both the microcapsules and SiO2 nanosphere composites because the surface-to-volume ratio is dramatically enlarged in both kinds of confinement. It is revealed from the XRD results that the novel solid–solid phase transition is observed only in the microencapsulated C16, which crystallizes into a stable triclinic phase via a mestastable rotator phase (RI). For the C16/SiO2 composite, however, no novel rotator phase emerges during the cooling process, and C16 crystallizes into a stable triclinic phase directly from the liquid state. Heterogeneous nucleation induced by the surface freezing phase is dominant in the microencapsulated sample and contributes to the emergence of the novel rotator phase, whereas heterogeneous nucleation induced by foreign crystallization nuclei dominates the C16/SiO2 composite, leading to phase transition behaviors similar to those of bulk C16.
Co-reporter:Tao Wen, Zujiang Xiong, Guoming Liu, Xiuqin Zhang, Sicco de Vos, Ryan Wang, Cornelis A.P. Joziasse, Fosong Wang, Dujin Wang
Polymer 2013 Volume 54(Issue 7) pp:1923-1929
Publication Date(Web):22 March 2013
DOI:10.1016/j.polymer.2013.02.010
In order to obtain a clear understanding to the interplay between the homogeneous crystal (α form) of PLA and its stereocomplex (SC) crystal, the crystalline behavior of PLA homopolymer under the surface drive force of SC and homopolymer fibers has been investigated in the present work. It was found that the nucleating density of the transcrystallization layer along the SC fiber was much lower than that along the homopolymer ones. Such morphologic difference between transcrystallization induced by SC and homopolymer fibers became more pronounced at higher crystallization temperature. The crystallization induction period (ti) of PLLA onto SC fiber was five times longer than that along homopolymer ones at 160 °C. However, if the blend fiber was predominantly containing α crystal, it could exhibit high nucleating capability as well as the homopolymer fibers. The results of TEM selected area electron diffraction (SAED) also revealed that the organization and orientation of α crystal were independent with the presence of SC substrate. Our results clearly indicated that there is no epitaxial relationship between PLA SC and α crystal.
Co-reporter:Guoming Liu, Xiuqin Zhang, Yufeng Liu, Xiuhong Li, Hongyu Chen, Kim Walton, Gary Marchand, Dujin Wang
Polymer 2013 Volume 54(Issue 4) pp:1440-1447
Publication Date(Web):18 February 2013
DOI:10.1016/j.polymer.2013.01.012
The structural evolution during uniaxial tensile deformation of isotactic polypropylene (iPP) and its blend with olefin block copolymer (OBC) was comparatively investigated by in-situ synchrotron X-ray scattering. Small angle X-ray scattering showed that cavitation in iPP/OBC blend took place at a smaller strain than that in neat iPP. The reorientation of the cavities in iPP/OBC occurred at a lower strain than that in iPP as well. Wide angle X-ray scattering was applied to study the crystal-mesophase transition and the orientation process. Compared to the sharp transition in neat iPP, the mesophase formation and orientation in iPP/OBC blend proceeded gradually. The mesophase content and degree of orientation of iPP matrix in iPP/OBC blend were much lower than that in neat iPP within the investigated strain range. By the combination of scattering results and morphological observations, a deformation mechanism based on strain distribution and fracture mechanics was proposed.
Co-reporter:Guoming Liu, Liuchun Zheng, Xiuqin Zhang, Chuncheng Li, Dujin Wang
Polymer 2013 Volume 54(Issue 25) pp:6860-6866
Publication Date(Web):27 November 2013
DOI:10.1016/j.polymer.2013.10.037
The crystalline structure evolution of poly(ethylene succinate) during tensile deformation was investigated by in-situ synchrotron X-ray scattering. Crystal phase transition from α to β form was confirmed to be fully reversible upon stress loading and unloading. An increase of long period was observed during the α–β crystal transition, which was attributed to the increase of both amorphous layer thickness and crystalline layer thickness (lamellar thickness). The crystalline layer thickness was scaled with the fraction of β crystal, and the change of which was in well agreement with the difference in the repeating length along the crystallographic c axis. Both the crystalline layer thickness and the amorphous layer thickness were fully recoverable. A possible molecular model was proposed to visualize the mechanism for the crystal transition and lamellar thickening.
Co-reporter:Guoming Liu;Xiuqin Zhang;Xiuhong Li;Hongyu Chen;Kim Walton;Dujin Wang
Journal of Applied Polymer Science 2012 Volume 125( Issue 1) pp:666-675
Publication Date(Web):
DOI:10.1002/app.36244
Abstract
This study examines the miscibility and mechanical properties of isotactic polypropylene (iPP) and olefin block copolymer (OBC) blends (70/30 wt %). The blends exhibit phase-separated morphology. The OBC domain size decreases with increasing the 1-octene content in the soft segment. The crystallization, melting behavior, and the long spacing of the iPP component in the blends are nearly the same as those of neat iPP, while the Tg of the iPP component shifts slightly to lower temperature. “Blocky” OBC is immiscible with iPP, while the soft segment rich polymers in OBC could be partially miscible with iPP. The impact strength of the blends is greatly increased with increasing the 1-octene content in the OBC soft segment. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
Co-reporter:Xiaoxiao Wei, Jian Yang, Zhiyong Li, Yunlan Su, Dujin Wang
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2012 Volume 401() pp:107-115
Publication Date(Web):5 May 2012
DOI:10.1016/j.colsurfa.2012.03.034
Calcium oxalate particles with different morphologies and phase structures were prepared by a facile precipitation reaction of sodium oxalate with calcium chloride in the presence of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) at different temperatures. The as-prepared products were characterized with scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the variations in the concentration of surfactants and temperatures significantly influenced the crystal structure, morphology, and particle size of the products. Cationic surfactant CTAB did not affect the crystal phase: calcium oxalate monohydrate (COM) was the only hydrate formed. Anionic surfactant SDS, however, not only changed the crystal shape, but also induced the formation of metastable calcium oxalate dihydrate (COD) with increasing surfactant concentration. High temperature favored the formation of COM. This work may provide new insights into the morphological control of calcium oxalate particles.Graphical abstractHighlights► Crystallization experiments were carried out at different temperatures. ► Calcium oxalate crystals with many interesting morphologies were synthesized in cationic and anionic surfactant systems. ► Surfactants affect the crystallization of calcium oxalate depending on their headgroup charge and state of aggregation.
Co-reporter:Qian Xing, Xiuqin Zhang, Xia Dong, Guoming Liu, Dujin Wang
Polymer 2012 Volume 53(Issue 11) pp:2306-2314
Publication Date(Web):9 May 2012
DOI:10.1016/j.polymer.2012.03.034
Two kinds of low molecular weight aliphatic amides, N, N′-ethylenebis (12-hydroxystearamide) (EBH) and N, N′-ethylenebisstearamide (EBSA), have been selected in present study to mediate the crystallization behavior of poly (L-lactic acid) (PLLA). The results showed that the crystallization rate of PLLA was significantly improved with the addition of EBH and EBSA, and EBH presented a stronger nucleating efficiency. The correlation between the variation of chain conformation during the early stages of isothermal crystallization and the enhancement of crystallization rate for pure PLLA and its mixtures was investigated by time-resolved FTIR. The formation of interchain conformational-ordered structure and intrachain 103 helix structure for amide-doped PLLA preceded that for pure PLLA, suggesting a stimulatory nucleating effect of EBH and EBSA. In the case of PLLA/EBH, the interchain interactions of –(COC + CH3) and –CH3 groups were faster than the –(CH3+CC) intrachain interactions, while the interchain interactions and the intrachain 103 helix formation were nearly synchronous for PLLA/EBSA. The hydrogen bond interaction between hydroxyl groups in EBH and the carbonyl groups in PLLA was proposed to be an important factor influencing the conformation variation during isothermal crystallization of PLLA.
Co-reporter:Dongsheng Fu, Yufeng Liu, Xia Gao, Yunlan Su, Guoming Liu, and Dujin Wang
The Journal of Physical Chemistry B 2012 Volume 116(Issue 10) pp:3099-3105
Publication Date(Web):February 15, 2012
DOI:10.1021/jp2125119
The crystallization behaviors of binary normal alkane (n-alkane) mixtures with a series of carbon number difference (denoted as Δn), both in the bulk state and in nearly monodisperse microcapsules, have been investigated by the combination of differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). As revealed by the DSC data, the surface freezing temperature (denoted as Ts) of spatially confined binary n-alkane mixtures with large Δn is lower than the calculated value due to the enrichment of shorter component in the surface freezing phase. More alkane molecules with shorter carbon chain are located on the interface between the inner shell of microcapsules and the bulk mixture, thus leading to the decrease of the average chain length of the surface freezing phase and corresponding lower Ts. Furthermore, XRD results have proved that the enhanced surface freezing phenomenon can contribute to the stabilization of the rotator phases in n-alkane mixtures and even induce the crossover of some certain rotator phase (RII) from transient to metastable. However, the decisive reason for such stabilization or crossover is attributed to the suppression of the orienting movement of alkane molecules toward their next-nearest neighbors within the layer of rotator phases.
Co-reporter:Tao Wen, Yong Zhou, Guoming Liu, Fosong Wang, Xiuqin Zhang, Dujin Wang, Hongyu Chen, Kim Walton, Gary Marchand, Joachim Loos
Polymer 2012 Volume 53(Issue 2) pp:529-535
Publication Date(Web):24 January 2012
DOI:10.1016/j.polymer.2011.11.062
The epitaxial crystallization behavior of olefin block copolymers (OBCs) on uniaxially oriented isotactic polypropylene (iPP) and high-density polyethylene (HDPE) films has been investigated by transmission electron microscopy (TEM). The crystallizable blocks of the OBCs under investigation were epitaxially nucleated by both iPP and HDPE substrates and epitaxial growth of OBC lamellae was observed. Epitaxial crystallization of the OBCs has been found for slow and fast cooling conditions from the melt which pointed to the strong interaction between the polyolefin substrates and the OBCs. However, the epitaxial morphology of the OBCs strongly depends on their octene concentration difference (ΔC8) between crystallizable and non-crystallizable blocks, which probably is related to the OBC segregation strength in the melt. With high ΔC8 the development of epitaxial crystallization of the OBC was restricted within isolated crystalline domains surrounded by the amorphous phase. In contrast, with low ΔC8 the oriented lamellae of the OBC were distributed homogeneously on iPP but formed separated crystalline domains on HDPE, which has a stronger nucleation capability than iPP on the crystalline OBC blocks because of its similar molecular architecture. Our study points to epitaxy as another reason for the strong interaction between OBC and polyolefins which causes the advanced compatibilization behavior of OBCs when compared with conventional random copolymers.
Co-reporter:Guoming Liu, Liuchun Zheng, Xiuqin Zhang, Chuncheng Li, Shichun Jiang, and Dujin Wang
Macromolecules 2012 Volume 45(Issue 13) pp:5487-5493
Publication Date(Web):June 27, 2012
DOI:10.1021/ma300530a
The structural evolution of poly(butylene succinate) (PBS) during tensile deformation was investigated by in situ synchrotron X-ray scattering. Crystal transition during stretching was identified at 30–90 °C. An increase of long period was observed during the α–β crystal transition, which was attributed to the increase of both amorphous layer thickness and crystalline layer thickness (lamellar thickness). The reversibility of crystal transition and correlation of lamellar thickening with crystal transition were confirmed by a “step-cycle” deformation measurement. The variation of the amorphous layer was partially recoverable, while the variation of lamellar thickness was nearly fully recoverable. The different repeating length in unit cell along the chain axis in different crystal forms resulted in the variation of the lamellar thickness. The different recoverability of structural parameters was interpreted by the different dynamics of the amorphous and crystalline phase.
Co-reporter:Xiuqin Zhang, Konrad Schneider, Guoming Liu, Jianhong Chen, Karsten Brüning, Dujin Wang, Manfred Stamm
Polymer 2012 Volume 53(Issue 2) pp:648-656
Publication Date(Web):24 January 2012
DOI:10.1016/j.polymer.2011.12.002
Cavitation and superstructure evolution of polymers during stretching play crucial roles to influence the mechanical properties of materials. In this study, we investigated deformation-mediated superstructures and cavitation of poly (l-lactide) (PLA) as well as their dependence on stretching temperatures by in-situ small-angle X-ray (SAXS) analysis coupled with mechanical testing. It is found that the cavitation and crystalline deformation are strongly influenced by stretching stress during deformation, which significantly depends on the stretching temperature. At lower stretching temperature (70 °C), the cavitation is initiated before the yielding and then stimulates the crystallite shearing. At higher stretching temperature (90 °C), however, the crystallites shear firstly and then crystalline deformation promotes the formation of cavities orientated along the stretching direction. High stretching temperature benefits the formation of relatively perfect crystals with high orientation. The results provide the basic knowledge of how to adjust the mechanical properties of polymer materials by controlling their superstructure in the deformation process.
Co-reporter:Haifeng Shi, Haixia Wang, John H. Xin, Xingxiang Zhang and Dujin Wang
Chemical Communications 2011 vol. 47(Issue 13) pp:3825-3827
Publication Date(Web):28 Feb 2011
DOI:10.1039/C0CC05245K
Crossover of mesophase to crystalline structure in the nanoconfinement crystallization process of frustrated side groups elucidates the critical crystal thickness dc or the length scale of side groups, which defines the transition process from mesophase (hexagonal and monoclinic phase) to crystalline phase (orthorhombic phase) of confined CH2 sequences in a given crystal size restriction.
Co-reporter:Dongsheng Fu, Yunlan Su, Baoquan Xie, Haijin Zhu, Guoming Liu and Dujin Wang
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 6) pp:2021-2026
Publication Date(Web):11 Jan 2011
DOI:10.1039/C0CP01173H
In the present investigation, the crystallization and phase transition behaviours of normal alkane (n-docosane) in microcapsules with a mean diameter of 3.6 μm were studied by the combination of differential scanning calorimetry (DSC), temperature-dependent X-ray diffraction (XRD) and variable-temperature solid-state nuclear magnetic resonance (VT solid-state 13C NMR). The DSC and VT solid-state 13C NMR results reveal that a surface freezing monolayer is formed prior to the bulk crystallization of the microencapsulated n-docosane. More interestingly, it is confirmed that after the bulk crystallization, the ordered triclinic phase coexists with the rotator phase I (RI) for the microencapsulated n-docosane. We argue that the reduction of the free energy difference between the two phases, resulting from the microencapsulation process, leads to the coexistence of the ordered triclinic and rotator phases of the normal alkanes.
Co-reporter:Dongsheng Fu, Yufeng Liu, Guoming Liu, Yunlan Su and Dujin Wang
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 33) pp:15031-15036
Publication Date(Web):26 Jul 2011
DOI:10.1039/C1CP21281H
The present work reports the confined crystallization behaviours of binary even–even normal alkane (n-alkane) mixtures of n-octadecane (n-C18H38) and n-eicosane (n-C20H42), which are microencapsulated in monodisperse microcapsules, using the combination of differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). A new metastable rotator phase (RII) absent in the bulk state, has been detected for the n-alkane mixture in confined geometry under all the investigated compositions. Such a crossover is attributed to the lower interfacial energy due to the same in-planar hexagonal structure of the surface monolayer and RII, as well as the weakened intermolecular interaction in alkane mixtures. This is the first time that RII is found in such a binary even–even n-alkane mixture that neither of the components contains RII phase in the crystallization process. Furthermore, based on the variation of alkane molecule conformation and in-planar structure with temperature, the correlations between the phase transition temperature and composition have been discussed.
Co-reporter:Yong Zhou, Haifeng Shi, Ying Zhao, Yongfeng Men, Shichun Jiang, Joerg Rottstegge and Dujin Wang
CrystEngComm 2011 vol. 13(Issue 2) pp:561-567
Publication Date(Web):21 Sep 2010
DOI:10.1039/C0CE00165A
We report on the confined crystallization and polymorphism behavior of a series of comb-like polymers (CS(n)Cs), which were prepared via an N-alkylation reaction between chitosan and n-alkyl bromides (n = 14–20). Analysis by temperature-dependent synchrotron X-ray scattering, Fourier transform infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance spectroscopy (NMR) and differential scanning calorimetry (DSC) revealed that the phase transition and crystalline structure were sensitively controlled by the length scale and the confinement state of alkyl groups, which could induce different packing structures and conformational variation behavior. Remarkably, phase transition from orthorhombic-hexagonal to monoclinic structure was observed for these side-chain polymers, demonstrating that the length scales of alkyl groups and the microstructure of polymeric backbones play an important role in the evolution of packing mode of nano-crystallites.
Co-reporter:Guoming Liu;Xiuqin Zhang;Chenyang Liu;Hongyu Chen;Kim Walton;Dujin Wang
Journal of Applied Polymer Science 2011 Volume 119( Issue 6) pp:3591-3597
Publication Date(Web):
DOI:10.1002/app.33035
Abstract
In the present work, statistical (EOCs) and block (OBCs) ethylene-octene copolymers, with similar densities and crystallinities, were used as impact modifiers of isotactic polypropylene (iPP), and the toughening effects of these two types of elastomers were compared. The viscosity curves of EOCs were similar to those of OBCs with equivalent melt flow rate (MFR), enabling a comparison of the viscosity ratio and elastomer type as independent variables. No distinct differences on the crystal forms and crystal perfection of iPP matrix in various blends were observed by thermal analysis. Morphological examination showed that OBCs form smaller dispersed domains than EOCs with similar MFRs. The flexural modulus, yield stress, stress and strain at break showed the same variation tendency for all the investigated polypropylene/elastomer blends. However, the room temperature Izod impact toughness of iPP/OBC blend was higher than that of iPP/EOC blend containing elastomer with the similar MFRs. The experimental results indicated that the compatibility of iPP/OBCs was much higher than that of iPP/EOCs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Co-reporter:Tao Yu;Faliang Luo;Ying Zhao;Dujin Wang;Fosong Wang
Journal of Applied Polymer Science 2011 Volume 120( Issue 2) pp:692-700
Publication Date(Web):
DOI:10.1002/app.33229
Abstract
Maleated poly(propylene carbonate)/calcium stearate (MAPPC/CaSt2) composite was prepared through melt-extruding poly(propylene carbonate) (PPC) with maleic anhydride and CaSt2. The processability, thermal stability, interaction between two components as well as the morphology of the composites were systematically characterized. The flow instability of biodegradable PPC was greatly alleviated due to the incorporation of stearate additive in polymer matrix. It was found that the MAPPC and MAPPC/CaSt2 composites were more thermostable than pristine PPC under melt-processing conditions. The melt fluidity of the composites was noticeably superior to that of MAPPC, arising from the lubricating effect of CaSt2 on the polymer/barrel wall interface as well as from the improvement of resistance to thermal degradation of the composite. The coordination interaction between MAPPC and calcium ion also contributes to the enhanced thermal stability and high melt stability of composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Co-reporter:Dongsheng Fu, Yufeng Liu, Yunlan Su, Guoming Liu, and Dujin Wang
The Journal of Physical Chemistry B 2011 Volume 115(Issue 16) pp:4632-4638
Publication Date(Web):April 5, 2011
DOI:10.1021/jp2004248
The crystallization behaviors of binary even−even normal alkane (n-alkane) mixtures (n-C18H38/n-C20H42, abbreviated as C18/C20) with different compositions, both in the bulk state and in nearly monodisperse microcapsules, have been investigated by the combination of differential scanning calorimetry and temperature-dependent X-ray diffraction. The solid−solid phase separation, usually observed during the cooling process of bulk samples, is greatly suppressed and even eliminated after being microencapsulated, with the orthorhombic-ordered phase dominating in the low-temperature crystal. Such a crystallization transition is attributed to the special interaction between the two even n-alkanes and the confined environment in microcapsules. The triclinic ordered phase, solely formed by the single even n-alkanes (C18 or C20), becomes less stable due to the weakening of the layered structure and the suppression of the terminal methyl−methyl interactions in the confined geometry, which favors the miscibility of the two components. Furthermore, besides the chain-length difference and the composition, the confined environment is proved to be another important factor to exert strong positive influence on suppressing the solid−solid phase separation of C18/C20 binary system.
Co-reporter:Xiuqin Zhang, Konrad Schneider, Guoming Liu, Jianhong Chen, Karsten Brüning, Dujin Wang, Manfred Stamm
Polymer 2011 Volume 52(Issue 18) pp:4141-4149
Publication Date(Web):18 August 2011
DOI:10.1016/j.polymer.2011.07.003
The present work explored the structure-property correlations for the biopolymer poly(l-lactic acid) (PLA) by studying deformation-mediated molecular orientation and crystallization. The structural and morphological variations of amorphous PLA under different strain rates were investigated. The result showed that strain rate significantly influences its strain-hardening behavior. The crystallinity and orientation as well as cavitation of deformed PLA increase with the increase of strain rates. The structure evolution has been divided into three potential stages: (i) at small strains (<100%), the crystallinity of PLA increases by orientation-induced crystallization; (ii) at intermediate strains (100%–160%), the crystallinity of deformed PLA slightly decreases due to the breakage of existing crystals under stress accompanying with newly formed voids and cavities; (iii) at high strains (>160%), the increasing number of oriented chains in the amorphous regions promotes the crystallization of PLA. Our study suggests that strain rate and stretching strain play important roles on modulating the crystallization and orientation of amorphous PLA.
Co-reporter:Guoming Liu, Yu Guan, Tao Wen, Xiwei Wang, Xiuqin Zhang, Dujin Wang, Xiuhong Li, Joachim Loos, Hongyu Chen, Kim Walton, Gary Marchand
Polymer 2011 Volume 52(Issue 22) pp:5221-5230
Publication Date(Web):13 October 2011
DOI:10.1016/j.polymer.2011.09.009
The mesophase separation and crystallization as well as the elastomeric properties of olefin multi-block copolymers (OBCs) are studied. The solid state morphologies of the OBCs are determined by the competition between mesophase separation and crystallization of hard blocks. The OBC with lower ΔC8 (octene content difference between soft and hard blocks) displays a spherulitic superstructure, while the OBC with higher ΔC8 exhibits mesophase separation. The two OBCs show very different elastomeric properties. Wide-angle X-ray scattering shows that the two OBCs have different deformation mechanisms. It is proposed that the cooperative deformation of crystalline phase makes an important contribution to the elastomeric properties.
Co-reporter:Dongsheng Fu, Yunlan Su, Baoquan Xie, Guoming Liu, Zhibo Li, Kai Jiang, Dujin Wang
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2011 Volume 384(1–3) pp:219-227
Publication Date(Web):5 July 2011
DOI:10.1016/j.colsurfa.2011.03.054
In the present work, in situ polymerization method was used to prepare nearly monodispersed microcapsules with long chain normal alkanes as core and melamine–formaldehyde (M–F) resin as shell at reaction temperature both above and below the cloud point of nonionic surfactant. A previously neglected point has been clarified, i.e., changing the reaction temperature is proved to be an effective way to tune the microcapsule size, surface pore size and density. Nano-scaled pores (from 5 to 200 nm) on the microcapsule surface were formed by the self-assembly template of nonionic surfactant micelles at different reaction temperatures. The dynamic morphological evolution in the encapsulation process was illustrated, for the first time, by scanning electron microscopy (SEM) at different reaction time. It is the alteration of the hydrophilic–lipophilic balance of crosslinked M–F preploymer in the polymerization process that leads the micelle droplets to migrate inside out, and consequently forms nano- or submicron-pores on the microcapsule surface. The prepared microcapsules have close inner space, providing a good 3-dimensional environment for the confined crystallization of alkanes within the polymeric shell. This methodology is versatile and effective for the synthesis of other porous microspheres, which can be applied potentially for encapsulating lipophilic functional materials.Graphical abstractHighlights► We examine the temperature effect on the size of surface pores and microcapsules. ► We investigate the morphological evolution during the encapsulation at different reaction time. ► The alteration of the hydrophilic–lipophilic balance of crosslinked preploymer plays an important role in the formation of the surface pores. ► Aggregation of micelles plays an important role for the formation of porous microcapsules.
Co-reporter:Fa-liang Luo;Xiu-qin Zhang;Wei Ning
Chinese Journal of Polymer Science 2011 Volume 29( Issue 2) pp:251-258
Publication Date(Web):2011 March
DOI:10.1007/s10118-010-1014-6
The early stage of polymer crystallization may be viewed as physical gelation process, i.e., the phase transition of polymer from liquid to solid. Determination of the gel point is of significance in polymer processing. In this work, the gelation behavior of poly(butylene succinate) (PBS) at different temperatures has been investigated by rheological method. It was found that during the isothermal crystallization process of PBS, both the storage modulus (G′) and the loss modulus (G″) increase with time, and the rheological response of the system varies from viscous-dominated (G′ < G″) to elastic-dominated (G′ > G″), meaning the phase transition from liquid to solid. The physical gel point was determined by the intersection point of loss tangent curves measured under different frequencies. The gel time (tc) for PBS was found to increase with increasing crystallization temperature. The relative crystallinity of PBS at the gel point is very low (2.5%–8.5%) and increases with increasing the crystallization temperature. The low crystallinity of PBS at the gel point suggests that only a few junctions are necessary to form a spanning network, indicating that the network is “loosely” connected, in another word, the critical gel is soft. Due to the elevated crystallinity at gel point under higher crystallization temperature, the gel strength Sg increases, while the relaxation exponent n decreases with increasing the crystallization temperature. These experimental results suggest that rheological method is an effective tool for verifying the gel point of biodegradable semi-crystalline polymers.
Co-reporter:Haijin Zhu;Robert Graf;Guangjin Hou;Ying Zhao;Dujin Wang;Hans W. Spiess
Macromolecular Chemistry and Physics 2010 Volume 211( Issue 10) pp:1157-1166
Publication Date(Web):
DOI:10.1002/macp.200900661
Co-reporter:Yunlan Su, Hengrui Yang, Wenxiong Shi, Hongxia Guo, Ying Zhao, Dujin Wang
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2010 Volume 355(1–3) pp:158-162
Publication Date(Web):20 February 2010
DOI:10.1016/j.colsurfa.2009.12.002
A systematic investigation on the influence of a series of synthesized triblock copolymers (PEG-b-PAA-b-PS, poly(ethylene glycol)-block-poly(acrylic acid)-block-poly(styrene)) on the crystallization, morphology and size of CaCO3 crystals was reported. The crystallization of vaterite is favored in the presence of copolymer 1 (PEG112-b-PAA40-b-PS37), which strongly depends on the polymer concentration. The fraction of spherical vaterite increased with the increase of the concentrations of copolymer 1. The molecular dynamics minimized structure of copolymer 2 (PEG112-b-PAA18-b-PS55) showed a close match between the spacings of the parallel-oriented carboxylate groups and the spacings of calcium ions in the calcite surface, which is favorable to the crystallization of calcite at all determined concentrations. The triblock copolymers could prohibit the phase transformation of vaterite to calcite, depending upon the block length of PAA middle segment and the concentration of the copolymers.
Co-reporter:Guoming Liu, Baoquan Xie, Dongsheng Fu, Yang Wang, Qiang Fu and Dujin Wang
Journal of Materials Chemistry A 2009 vol. 19(Issue 36) pp:6605-6609
Publication Date(Web):20 Jul 2009
DOI:10.1039/B901102A
Nearly monodisperse microcapsules with controllable porous surface morphologies were prepared by the in situpolymerization of melamine and formaldehyde with a template of nonionic surfactant micelles above the cloud point, inside which normal alkanes can be either encapsulated as phase change material or removed to obtain porous hollow spheres. The experimental results indicate that both the size and density of the pores on the microcapsule surface are tunable by changing the amount of core material (normal alkane) or the ratio of the polymer shell material to core material. The formation mechanism of the surface porosity was investigated by considering the polymerization temperature and the concentration of nonionic surfactants, which were used as the emulsifiers of core material droplets. The thermal gravimetry analysis proved that the microcapsules are thermally stable, and the heat treatment provided a new approach to preparing porous hollow microspheres.
Co-reporter:Tao Yu, Yong Zhou, Kaipeng Liu, Ying Zhao, Erqiang Chen, Fosong Wang, Dujin Wang
Polymer Degradation and Stability 2009 Volume 94(Issue 2) pp:253-258
Publication Date(Web):February 2009
DOI:10.1016/j.polymdegradstab.2008.10.021
Poly(propylene carbonate) (PPC), a typical aliphatic polycarbonate, has attracted much attention during the last two decades due to its biodegradability and commercializing perspective. However, the application of this material as thermoplastics has been limited by its poor thermal stability. Metal soaps, such as calcium stearate (CaSt2), are important processing additives in plastics industry. In the present work, PPC–CaSt2 complexes were prepared, the thermal stability of which was investigated by thermogravimetric analysis (TGA). The results show that the complexes are more thermal stable than pure PPC material. Supramolecular lamellar mesomorphous structures of the complexes were corroborated by the combination of small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and polarizing optical microscopy (POM). Metal ion coordination of CaSt2 to flexible PPC chains was determined by Fourier transform infrared spectroscopy (FT-IR). This coordination interaction plays the key role in improving the thermal property of PPC and constructing the self-organized structure of the complexes.
Co-reporter:Changming Wang, Ying Zhao, Jinliang Song, Buxing Han and Dujin Wang
New Journal of Chemistry 2009 vol. 33(Issue 9) pp:1841-1844
Publication Date(Web):30 Jul 2009
DOI:10.1039/B9NJ00326F
Integrated micro-sized spherulites of ultrahigh molecular weight polyethylene (UHMWPE), with one clear homogeneous nucleation site and sheaf-like lamellae, have been successfully prepared from supercritical fluid of ethanol, supplying a propagating stage from sheaf-like dendrite to final spherical crystal.
Co-reporter:Rongbo Li;Xiuqin Zhang;Lijuan Zhou;Jinyong Dong;Dujin Wang
Journal of Applied Polymer Science 2009 Volume 111( Issue 2) pp:826-832
Publication Date(Web):
DOI:10.1002/app.29118
Abstract
In situ compatibilization of polypropylene (PP) and polystyrene (PS) was achieved by combinative application of tetraethyl thiuram disulfide (TETD) as degradation inhibitor and di-tert-butyl peroxide as degradation initiator in the process of reactive extrusion. The PP/PS blends obtained were systematically investigated by rheological measurement, scanning electron microscopy, and differential scanning calorimetry. The results indicate that peroxide-induced degradation of PP can be effectively depressed by adding TETD, which may favor the formation of PP-g-PS copolymer during melt processing. The PP-g-PS copolymer formed may act as an in situ compatibilizer for PP/PS blends, and subsequently decreases the size of dispersed PS phase and changes both rheological and thermal properties of the blends. Based on the present experimental results, the mechanisms for the controlled degradation of PP and in situ formation of PP-g-PS copolymer in the PP/PS blends have been proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Co-reporter:Yong Zhou, Hui Niu, Lei Kong, Ying Zhao, Jin-Yong Dong, Dujin Wang
Polymer 2009 50(19) pp: 4690-4695
Publication Date(Web):
DOI:10.1016/j.polymer.2009.07.042
Co-reporter:Yunlan Su, Dexiu Wang, Hengrui Yang, Dujin Wang
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2009 Volume 342(1–3) pp:122-126
Publication Date(Web):15 June 2009
DOI:10.1016/j.colsurfa.2009.04.027
Calcite crystals elongated along the c-axis and capped by (1 0 4) rhombohedral faces were grown in the solutions of two kinds of triblock copolymers poly (ethylene glycol)-block-poly (acrylic acid)-block-poly (n-butyl acrylate) (PEG-b-PAA-b-PnBA) with different PAA block length. The copolymer with 3:1 PEG:PAA block ratio facilitates the formation of spindle-shaped calcite elongated along the c-axis and with curved (1 0 0) or (1 1 0) prismatic faces. CaCO3 obtained from the copolymer with 6:1 PEG:PAA block ratio exhibits stack-like calcite elongated along the c-axis and with no newly developed faces. The formation of elongated calcite could be due to the aggregation of nanoparticles via an oriented attachment mechanism. The calcite crystals recovered their rhombohedral {1 0 4} faces gradually with decreasing PAA block length from 3:1 to 6:1 PEG:PAA block ratio, which could be attributed to the weakening of the inhibition efficiency of the PAA block on the non-rhombohedral planes.
Co-reporter:Kai Jiang, Yunlan Su, Baoquan Xie, Yanfeng Meng and Dujin Wang
The Journal of Physical Chemistry B 2009 Volume 113(Issue 11) pp:3269-3272
Publication Date(Web):February 24, 2009
DOI:10.1021/jp811496x
The crystallization of binary n-alkane solid solution n-C18H38/n-C19H40 = 90/10 (molar ratio) (abbreviated as C18/C19 = 90/10) and the microencapsulated counterpart (abbreviated as m-C18/C19 = 90/10) has been investigated by a combination of differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). The solid−solid phase separation was obviously detected in C18/C19 = 90/10 by XRD, which is absent in m-C18/C19 = 90/10. The XRD data also show that the chain packing of m-C18/C19 = 90/10 is different from that of bulk C18/C19 = 90/10. The packing mode of m-C18/C19 = 90/10 molecular chains is unique; i.e., the n-alkane chains pack along the longitudinal direction and the neighboring layers interdigitate with each other, subsequently resulting in the deconstruction of lamellar ordering. The extinction of phase separation in m-C18/C19 = 90/10 can be understood in terms of the suppression of longitudinal chain diffusion caused by the special three-dimensional confinement effect provided by microcapsules.
Co-reporter:Rongbo Li, Xiuqin Zhang, Ying Zhao, Xuteng Hu, Xutao Zhao, Dujin Wang
Polymer 2009 50(21) pp: 5124-5133
Publication Date(Web):
DOI:10.1016/j.polymer.2009.09.026
Co-reporter:Baoquan Xie, Haifeng Shi, Guoming Liu, Yong Zhou, Yang Wang, Ying Zhao and Dujin Wang
Chemistry of Materials 2008 Volume 20(Issue 9) pp:3099
Publication Date(Web):April 9, 2008
DOI:10.1021/cm7034618
Microcapsules with controllable porous surface morphology and good monodispersity were prepared using the one-step synthetic strategy by employing the self-assembly template of nonionic surfactant micelles above its cloud point. Both the pore size (from 100 to 400 nm) and pore density are tunable by changing the amount of core materials or the ratio of core material to shell material. This methodology provides a versatile and effective route for preparation of porous microsphere materials, which can encapsulate lipophilic functional compounds.
Co-reporter:Baoquan Xie, Guoming Liu, Shichun Jiang, Ying Zhao and Dujin Wang
The Journal of Physical Chemistry B 2008 Volume 112(Issue 42) pp:13310-13315
Publication Date(Web):September 25, 2008
DOI:10.1021/jp712160k
In this paper, the confined crystallization and phase transition behaviors of n-octadecane in microcapsules with a diameter of about 3 μm were studied with the combination of differential scanning calorimetry (DSC), temperature dependent Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The main discovery is that the microencapsulated n-octadecane crystallizes into a stable triclinic phase via a mestastable rotator phase (RI), which emerges as a transient state for the bulk n-octadecane and is difficult to be detected by the commonly used characterization methods. As evident from the DSC measurement, a surface freezing monolayer, which is formed at the interface between the microcapsule inner wall and n-octadecane, induces the crossover of the RI from transient to metastable. We argue that the existence of the surface freezing monolayer decreases the nucleating potential barrier of the RI phase, and consequently the lower relative nucleation barrier in the confined geometry turns the transient RI phase into a metastable one.
Co-reporter:Kai Jiang, Yunlan Su, Baoquan Xie, Shichun Jiang, Ying Zhao and Dujin Wang
The Journal of Physical Chemistry B 2008 Volume 112(Issue 51) pp:16485-16489
Publication Date(Web):December 2, 2008
DOI:10.1021/jp807347d
The condensed structure of normal alkane (n-alkane) mixtures in confined geometry is an interesting topic concerning the difference in crystallization behavior of odd and even alkanes. In the present work, the crystallization of mixtures of normal octadecane (n-C18H38) and normal nonadecane (n-C19H40) in microcapsules with narrow size distribution was investigated using the combination of differential scanning calorimetry (DSC) and X-ray diffraction (XRD). A surface freezing monolayer for microencapsulated n-C18H38, n-C19H40, and their mixture was detected by DSC, which for the mixture is a mixed homogeneous crystalline phase with continuous change in the composition. A more stable rotator phase (RI) was observed for the microencapsulated n-C18H38/n-C19H40 = 95/5 (molar ratio) mixture, confirmed by an increased supercooling of the transition from RI to stable phase compared to that of the mixture in bulk. Two nucleation mechanisms were speculated as “liquid-to-solid” heterogeneous nucleation and “solid-to-solid” homogeneous nucleation, which occur at different crystallization stages in microcapsules and might be attributed to the surface effect and confinement effect, respectively, in the confined geometry.
Co-reporter:Tao Yu, Yong Zhou, Ying Zhao, Kaipeng Liu, Erqiang Chen, Dujin Wang and Fosong Wang
Macromolecules 2008 Volume 41(Issue 9) pp:3175-3180
Publication Date(Web):April 17, 2008
DOI:10.1021/ma7020562
We report a simple method to prepare biodegradable polymer−amphiphile complexes by solution mixing of poly(propylene carbonate) (PPC) with octadecanoic acid (OA). The complexes were characterized by combination of thermogravimetry analysis (TGA), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), polarizing optical microscopy (POM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR). Compared with the amorphous PPC copolymer, the PPC−OA-x complexes show excellent thermal stability and form thermotropic liquid crystalline state without rigid mesogenic units. The corresponding mechanism has been proposed to elucidate the observed phenomena. The stabilization effect induced by hydrogen-bonding interactions between PPC and OA molecules is responsible for the thermostability and formation of liquid crystalline state. The present findings may extend the applications of such biodegradable aliphatic polycarbonate by improving its glass transition temperature and thermoplastic processability.
Co-reporter:Yaping Huang;Qiang Shen;Weiping Sui;Meili Guo;Ying Zhao
Colloid and Polymer Science 2007 Volume 285( Issue 6) pp:
Publication Date(Web):2007 March
DOI:10.1007/s00396-006-1606-4
An amphiphilic derivative of carboxymethylchitosan (CMCS), (2-hydroxyl-3-butoxyl)propyl-CMCS (HBP-CMCS), was used as an organic additive in the precipitation process of calcium carbonate (CaCO3). HBP-CMCS molecules can interact with calcium ions, the functional groups of which act as active sites for the nucleation and crystallization of CaCO3. Simultaneously, HBP-CMCS molecule also functionalizes as a colloidal stabilizer to prohibit the sedimentation of the grown CaCO3 crystals, depending upon the molar ratio of the initial Ca2+ ions to the repeat units of HBP-CMCS molecules. The combination investigations of scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy on the precipitated CaCO3 crystals proved that concentrations of HBP-CMCS and Ca2+ exert great influence on the crystallization habit of CaCO3, such as the nucleation, growth, morphology, crystal form, etc. The formation of the peanut-shaped CaCO3 particles suggests the template effect of HBP-CMCS molecules on the aggregation behavior of CaCO3 nanocrystals.
Co-reporter:Lihong He;Yanhong Zhang;Lixia Ren;Yongming Chen;Hao Wei;Dujin Wang
Macromolecular Chemistry and Physics 2006 Volume 207(Issue 7) pp:684-693
Publication Date(Web):28 MAR 2006
DOI:10.1002/macp.200500542
Summary: A water-soluble diblock copolymer composed of poly(ethylene glycol) (PEG) and a cylindrical poly(acrylic acid) (PAA) brush is reported. It is prepared by a ‘grafting from’ approach using stepwise atom transfer radical polymerization combined with group transformation. Uniform molecular brushes, PEG113-b-P(MA-g-PAA26)169, are thus prepared as indicated by atom force microscopy analysis. This PAA densely grafted polymer is used to induce the crystallization of calcium carbonate in aqueous solution. Different experimental conditions, fast mixing reactions and static diffusion methods, are applied to explore the effect of polymer brushes on the crystallization, which is characterized by scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis.
Co-reporter:Lihong He;Yanhong Zhang;Lixia Ren;Yongming Chen;Hao Wei;Dujin Wang
Macromolecular Chemistry and Physics 2006 Volume 207(Issue 7) pp:
Publication Date(Web):30 MAR 2006
DOI:10.1002/macp.200690010
Co-reporter:Surong Zhou;Haifeng Shi;Ying Zhao;Shichun Jiang;Yonglai Lu;Yuanli Cai;Dujin Wang;Charles C. Han;Duanfu Xu
Macromolecular Rapid Communications 2005 Volume 26(Issue 4) pp:226-231
Publication Date(Web):7 FEB 2005
DOI:10.1002/marc.200400540
Summary: The microstructure and phase transformation of a highly-branched polyethyleneimine/octadecanoic acid (PEI(OA)1.0) complex were investigated using a combination of DSC, XRD, optical polarised microscopy and temperature dependent FT-IR spectroscopy. A mesogen-free thermotropic liquid crystalline state was observed in a certain temperature region. The strong ionic interaction between COO− (from OA) and NH (from PEI) and the hydrophobic interaction between the alkyl side chains contributes to the formation of a thermotropic liquid crystalline structure.
Co-reporter:Zhiqiang Su;Ying Zhao;Ning Kang;Xiuqin Zhang;Yizhuang Xu;Jinguang Wu;Dujin Wang;Charles C. Han;Duanfu Xu;Ying Zhao;Ning Kang;Yizhuang Xu;Jinguang Wu;Xiuqin Zhang;Dujin Wang;Zhiqiang Su;Duanfu Xu;Charles C. Han
Macromolecular Rapid Communications 2005 Volume 26(Issue 11) pp:895-898
Publication Date(Web):2 JUN 2005
DOI:10.1002/marc.200500075
Summary: High-resolution FT-IR spectroscopy has been used for the first time to characterize the variation of the unit cell dimensions of high-density polyethylene (HDPE). In combination with the unit cell parameters of HDPE measured at different temperatures by Swan using wide-angle X-ray diffraction, the relationship between the rocking band shift (730 cm−1) and the change of the unit cell volume of HDPE has been established.
Co-reporter:Xiu-Qin Zhang;Ying Zhao;Hai-Feng Shi;Charles C. Han;Xia Dong;Duan-Fu Xu
Journal of Polymer Science Part B: Polymer Physics 2005 Volume 43(Issue 20) pp:2924-2936
Publication Date(Web):8 SEP 2005
DOI:10.1002/polb.20573
Low syndiotactic polypropylene (sPP; rrrr = 80%) films were isothermally crystallized at 0 °C (sample S0) and 90 °C (sample S90) for 65 h, respectively. Fourier transform infrared spectroscopy, differential scanning calorimetry, and wide-angle X-ray diffraction were used to characterize the structure transformation and orientation behavior of samples S0 and S90 at both stretched and stress-relaxed states. It was found that stretching (λ = 0–700%) induces the transformation of the chain conformation from helical to trans-planar form for both S0 and S90 films. The stretched S0 and S90 samples show well oriented trans-planar chains as well as partially retained helices. Simultaneously, crystalline phase transformation occurs during the stretching and relaxing processes of the investigated sPP samples, i.e., stable form I crystals can be transformed into metastable form III or mesophase by stretching samples, and vice versa. For stretched S0 sample, form III with trans-planar conformation, which generally exists in highly stretched sPP, cannot be observed, even at higher strains. For sample S90, however, stretching might induce the formation of both the form III crystals and mesophase with trans-planar chains; releasing the tension, form III again gets converted into trans-planar mesophase and form I crystals. In the stretched and stress-relaxed states of samples S0 and S90, the difference of the delicate orientation behavior and relative content of chain conformation and crystalline form can be attributed to the different heat-treating methods of the low syndiotacticity sPP. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2924–2936, 2005
Co-reporter:Changcheng He;Xia Dong;Xiuqin Zhang;Dujin Wang;Duanfu Xu
Journal of Applied Polymer Science 2004 Volume 91(Issue 5) pp:2980-2983
Publication Date(Web):14 JAN 2004
DOI:10.1002/app.13500
The morphology of PA66/Kevlar-129 fiber specimens was investigated by means of polarized optical microscopy and scanning electron microscopy. The results indicated that, at crystallization temperatures ranging from 100 to 220°C, the transcrystallinity (TC) interphase always occurs. Both the TC interphase and spherulite morphology were present under various crystallization conditions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2980–2983, 2004
Co-reporter:Xiuqin Zhang;Mingshu Yang;Ying Zhao;Shimin Zhang;Xia Dong;Xuexin Liu;Dujin Wang;Duanfu Xu
Journal of Applied Polymer Science 2004 Volume 92(Issue 1) pp:552-558
Publication Date(Web):3 FEB 2004
DOI:10.1002/app.20039
Polypropylene (PP)/organomontmorillonite (OMMT) nanocomposites have been successfully prepared by melt intercalation by using the conventional method of twin-screw extrusion and subsequently submitted for melt-spinning. The structure and properties of the PP/clay nanocomposites and hybrid fibers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and crystallization dynamics, etc. The organoclay layers were found to disperse in the PP resin at the nanometer level. The nanoscaled OMMT layers, dispersed in the PP matrix, actually played the role of heterogeneous nuclei species in the process of PP crystallization and increased the nucleation speed of the composites, hereby leading to the increase of crystallization rate of the as-spun fiber. Meanwhile, it was found that the crystallinity of PP/OMMT hybrid fibers is much higher than that of pure PP fiber at the same draw ratios, whereas the orientation of PP/OMMT hybrid fibers is much lower than that of pure PP fiber at the same draw ratios. Because of the effective intercalation of OMMT into PP matrix, the nanocomposites have good spinnability, and the moisture absorption of the final PP fiber is improved. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 552–558, 2004
Co-reporter:Qiang Shen, Hao Wei, Ying Zhao, Du-Jin Wang, Li-Qiang Zheng, Duan-Fu Xu
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2004 Volume 251(1–3) pp:87-91
Publication Date(Web):20 December 2004
DOI:10.1016/j.colsurfa.2004.08.024
The crystallization of calcium carbonate was conducted by the reaction of sodium carbonate with calcium chloride in the presence of polyvinylpyrrolidone (PVP), sodium dodecylbenzene sulfonate (SDBS), or the mixture of PVP and SDBS, respectively. The morphology and polymorphism of these CaCO3 crystals were characterized with scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). The results showed that the organic additives and their self-assemblies turn out to be important factors to affect the crystallization habit of CaCO3. In particular, the controlling effect on the morphology depends upon not only the total concentration of PVP and SDBS, but also the relative concentration ratio of PVP to SDBS.
Co-reporter:Xiao Kuang, Guoming Liu, Xia Dong and Dujin Wang
Inorganic Chemistry Frontiers 2017 - vol. 1(Issue 1) pp:NaN118-118
Publication Date(Web):2016/08/19
DOI:10.1039/C6QM00094K
Smart polymers based on covalent adaptive networks (CANs) with reversible covalent bonds have drawn tremendous attention in the past few years. The relaxation properties of CANs polymers play an important role because of their stimuli-responsive capability. Here, we elucidate the correlation between the stress relaxation dynamics and reaction thermochemistry of CANs polymers. Diels–Alder (DA) reaction based cross-linked elastomers are utilized as model CANs polymers. In situ FTIR data reveals the dynamic reaction kinetics and thermodynamics in the solid state. The influence of cross-linking density on the temperature-dependent stress relaxation time of the CANs polymers well above the gel point can be normalized by the relative distance to the gel point conversion. Combining the Semenov–Rubinstein theory and Arrhenius' law, a simple scaling relationship between normalized relaxation time and reaction kinetics is established for CANs polymers.
Co-reporter:Haifeng Shi, Haixia Wang, John H. Xin, Xingxiang Zhang and Dujin Wang
Chemical Communications 2011 - vol. 47(Issue 13) pp:NaN3827-3827
Publication Date(Web):2011/02/28
DOI:10.1039/C0CC05245K
Crossover of mesophase to crystalline structure in the nanoconfinement crystallization process of frustrated side groups elucidates the critical crystal thickness dc or the length scale of side groups, which defines the transition process from mesophase (hexagonal and monoclinic phase) to crystalline phase (orthorhombic phase) of confined CH2 sequences in a given crystal size restriction.
Co-reporter:Haifeng Shi, Ying Zhao, Xia Dong, Yong Zhou and Dujin Wang
Chemical Society Reviews 2013 - vol. 42(Issue 5) pp:NaN2099-2099
Publication Date(Web):2012/12/17
DOI:10.1039/C2CS35350D
Comb-like polymers with flexible side chains chemically pended onto a polymeric backbone afford some unusual properties due to their hierarchical structures, such as nanoscale confined crystallisation, phase transition and conformational variations, length scale effects, etc. Considerable attention has been paid to these featured polymers, regarding their importance in understanding the correlation between hierarchical structure and the assembled morphologies. In this review, we reviewed the recent research progress on the structure–property correlations of comb-like polymers. This article brings together and highlights the fabrication, structure determination and morphology characterization for comb-like polymers, especially for nanostructured packing patterns and frustrated mobility of chain segments from the selected examples.
Co-reporter:Zhiyong Li, Yunlan Su, Baoquan Xie, Xianggui Liu, Xia Gao and Dujin Wang
Journal of Materials Chemistry A 2015 - vol. 3(Issue 9) pp:NaN1778-1778
Publication Date(Web):2015/01/13
DOI:10.1039/C4TB01653J
A novel physically linked double-network (DN) hydrogel based on natural polymer konjac glucomannan (KGM) and synthetic polymer polyacrylamide (PAAm) has been successfully developed. Polyvinyl alcohol (PVA) was used as a macro-crosslinker to prepare the PVA–KGM first network hydrogel by a cycle freezing and thawing method for the first time. Subsequent introduction of a secondary PAAm network resulted in super-tough DN hydrogels. The resulting PVA–KGM/PAAm DN hydrogels exhibited unique ability to be freely shaped, cell adhesion properties and excellent mechanical properties, which do not fracture upon loading up to 65 MPa and a strain above 0.98. The mechanical strength and microstructure of the DN hydrogels were investigated as functions of acrylamide (AAm) content and freezing and thawing times. A unique embedded micro-network structure was observed in the PVA–KGM/PAAm DN gels and accounted for the significant improvement in toughness. The fracture mechanism is discussed based on the yielding behaviour of these physically linked hydrogels.
Co-reporter:Guoming Liu, Baoquan Xie, Dongsheng Fu, Yang Wang, Qiang Fu and Dujin Wang
Journal of Materials Chemistry A 2009 - vol. 19(Issue 36) pp:NaN6609-6609
Publication Date(Web):2009/07/20
DOI:10.1039/B901102A
Nearly monodisperse microcapsules with controllable porous surface morphologies were prepared by the in situpolymerization of melamine and formaldehyde with a template of nonionic surfactant micelles above the cloud point, inside which normal alkanes can be either encapsulated as phase change material or removed to obtain porous hollow spheres. The experimental results indicate that both the size and density of the pores on the microcapsule surface are tunable by changing the amount of core material (normal alkane) or the ratio of the polymer shell material to core material. The formation mechanism of the surface porosity was investigated by considering the polymerization temperature and the concentration of nonionic surfactants, which were used as the emulsifiers of core material droplets. The thermal gravimetry analysis proved that the microcapsules are thermally stable, and the heat treatment provided a new approach to preparing porous hollow microspheres.
Co-reporter:Dongsheng Fu, Yunlan Su, Baoquan Xie, Haijin Zhu, Guoming Liu and Dujin Wang
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 6) pp:NaN2026-2026
Publication Date(Web):2011/01/11
DOI:10.1039/C0CP01173H
In the present investigation, the crystallization and phase transition behaviours of normal alkane (n-docosane) in microcapsules with a mean diameter of 3.6 μm were studied by the combination of differential scanning calorimetry (DSC), temperature-dependent X-ray diffraction (XRD) and variable-temperature solid-state nuclear magnetic resonance (VT solid-state 13C NMR). The DSC and VT solid-state 13C NMR results reveal that a surface freezing monolayer is formed prior to the bulk crystallization of the microencapsulated n-docosane. More interestingly, it is confirmed that after the bulk crystallization, the ordered triclinic phase coexists with the rotator phase I (RI) for the microencapsulated n-docosane. We argue that the reduction of the free energy difference between the two phases, resulting from the microencapsulation process, leads to the coexistence of the ordered triclinic and rotator phases of the normal alkanes.
Co-reporter:Dongsheng Fu, Yufeng Liu, Guoming Liu, Yunlan Su and Dujin Wang
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 33) pp:NaN15036-15036
Publication Date(Web):2011/07/26
DOI:10.1039/C1CP21281H
The present work reports the confined crystallization behaviours of binary even–even normal alkane (n-alkane) mixtures of n-octadecane (n-C18H38) and n-eicosane (n-C20H42), which are microencapsulated in monodisperse microcapsules, using the combination of differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). A new metastable rotator phase (RII) absent in the bulk state, has been detected for the n-alkane mixture in confined geometry under all the investigated compositions. Such a crossover is attributed to the lower interfacial energy due to the same in-planar hexagonal structure of the surface monolayer and RII, as well as the weakened intermolecular interaction in alkane mixtures. This is the first time that RII is found in such a binary even–even n-alkane mixture that neither of the components contains RII phase in the crystallization process. Furthermore, based on the variation of alkane molecule conformation and in-planar structure with temperature, the correlations between the phase transition temperature and composition have been discussed.
![Poly[oxy[(2E)-1,4-dioxo-2-butene-1,4-diyl]oxy-1,4-butanediyl]](http://img.cochemist.com/ccimg/36900/36813-67-9.png)
![Poly[oxy[(2E)-1,4-dioxo-2-butene-1,4-diyl]oxy-1,4-butanediyl]](http://img.cochemist.com/ccimg/36900/36813-67-9_b.png)
![Poly[imino-1,6-hexanediylimino(1,12-dioxo-1,12-dodecanediyl)]](http://img.cochemist.com/ccimg/25000/24936-74-1.png)
![Poly[imino-1,6-hexanediylimino(1,12-dioxo-1,12-dodecanediyl)]](http://img.cochemist.com/ccimg/25000/24936-74-1_b.png)
![POLY[OXY[(1R)-1-METHYL-2-OXO-1,2-ETHANEDIYL]]](http://img.cochemist.com/ccimg/27000/26917-25-9.png)
![POLY[OXY[(1R)-1-METHYL-2-OXO-1,2-ETHANEDIYL]]](http://img.cochemist.com/ccimg/27000/26917-25-9_b.png)
![Poly[oxy[(1S)-1-methyl-2-oxo-1,2-ethanediyl]]](http://img.cochemist.com/ccimg/26200/26161-42-2.png)
![Poly[oxy[(1S)-1-methyl-2-oxo-1,2-ethanediyl]]](http://img.cochemist.com/ccimg/26200/26161-42-2_b.png)
![Stannane, 1,1'-[4,8-bis[(2-butyloctyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]bis[1,1,1-trimethyl-](/data/chemimg/154400/1271439-08-7.png)
![Stannane, 1,1'-[4,8-bis[(2-butyloctyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]bis[1,1,1-trimethyl-](/data/chemimg/154400/1271439-08-7_b.png)
![Dithieno[3,2-e:2',3'-g]-2,1,3-benzothiadiazole](/data/chemimg/154400/1256138-50-7.png)
![Dithieno[3,2-e:2',3'-g]-2,1,3-benzothiadiazole](/data/chemimg/154400/1256138-50-7_b.png)
![Benzo[2,1-b:3,4-b']dithiophene-4,5-diamine](/data/chemimg/154400/1256138-44-9.png)
![Benzo[2,1-b:3,4-b']dithiophene-4,5-diamine](/data/chemimg/154400/1256138-44-9_b.png)
![Stannane, 1,1'-[4,8-bis[(2-hexyldecyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]bis[1,1,1-trimethyl-](/data/chemimg/154400/1254985-74-4.png)
![Stannane, 1,1'-[4,8-bis[(2-hexyldecyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]bis[1,1,1-trimethyl-](/data/chemimg/154400/1254985-74-4_b.png)
![Benzo[1,2-b:4,5-b']dithiophene, 4,8-bis[(2-hexyldecyl)oxy]-](/data/chemimg/154400/1254985-73-3.png)
![Benzo[1,2-b:4,5-b']dithiophene, 4,8-bis[(2-hexyldecyl)oxy]-](/data/chemimg/154400/1254985-73-3_b.png)
![Aluminate(2-), borate[μ-[orthoborato(3-)-κO:κO']][μ-[orthoboric acid trimol. dianhydridato(5-)]]-, hydrogen, compd. with methanamine, hydrate (1:2:2:1)](http://img.cochemist.com/ccimg/1253900/1253816-54-4.png)
![Aluminate(2-), borate[μ-[orthoborato(3-)-κO:κO']][μ-[orthoboric acid trimol. dianhydridato(5-)]]-, hydrogen, compd. with methanamine, hydrate (1:2:2:1)](http://img.cochemist.com/ccimg/1253900/1253816-54-4_b.png)
![Aluminate(2-), borate[μ-[orthoborato(3-)-κO:κO']][μ-[orthoboric acid trimol. dianhydridato(5-)]]-, hydrogen, compd. with methanamine, hydrate (1:2:2:2)](http://img.cochemist.com/ccimg/1253900/1253816-51-1.png)
![Aluminate(2-), borate[μ-[orthoborato(3-)-κO:κO']][μ-[orthoboric acid trimol. dianhydridato(5-)]]-, hydrogen, compd. with methanamine, hydrate (1:2:2:2)](http://img.cochemist.com/ccimg/1253900/1253816-51-1_b.png)
![1,3-Propanediol, 2,2-bis[(4S)-4-(1,1-dimethylethyl)-4,5-dihydro-2-oxazolyl]-](/data/chemimg/106800/871576-28-2.png)
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![4H-Imidazol-4-one, 1,5-dihydro-5-[(4-hydroxyphenyl)methylene]-](http://img.cochemist.com/ccimg/350600/350578-12-0.png)
![4H-Imidazol-4-one, 1,5-dihydro-5-[(4-hydroxyphenyl)methylene]-](http://img.cochemist.com/ccimg/350600/350578-12-0_b.png)
![Aziridine, 2-decyl-1-[(4-methylphenyl)sulfonyl]-](http://img.cochemist.com/ccimg/211000/210972-34-2.png)
![Aziridine, 2-decyl-1-[(4-methylphenyl)sulfonyl]-](http://img.cochemist.com/ccimg/211000/210972-34-2_b.png)
![Propanoic acid,2-[4-[(7-chloro-2-quinoxalinyl)oxy]phenoxy]-](http://img.cochemist.com/ccimg/157500/157435-10-4.png)
![Propanoic acid,2-[4-[(7-chloro-2-quinoxalinyl)oxy]phenoxy]-](http://img.cochemist.com/ccimg/157500/157435-10-4_b.png)
![[1,1'-Biphenyl]-4-carboxaldehyde, 4'-ethenyl-](/data/chemimg/106900/155686-71-8.png)
![[1,1'-Biphenyl]-4-carboxaldehyde, 4'-ethenyl-](/data/chemimg/106900/155686-71-8_b.png)
![Aziridine, 2-hexyl-1-[(4-methylphenyl)sulfonyl]-](http://img.cochemist.com/ccimg/149000/148961-16-4.png)
![Aziridine, 2-hexyl-1-[(4-methylphenyl)sulfonyl]-](http://img.cochemist.com/ccimg/149000/148961-16-4_b.png)
![Benzenemethanol, 4-nitro-α-[(1R)-1-nitroethyl]-, (αS)-rel-](/data/chemimg/106700/142839-99-4.png)
![Benzenemethanol, 4-nitro-α-[(1R)-1-nitroethyl]-, (αS)-rel-](/data/chemimg/106700/142839-99-4_b.png)
![N-[1-(2,3-DIOLEYLOXY)PROPYL]-N,N,N-TRIMETHYLAMMONIUM CHLORIDE](http://img.cochemist.com/ccimg/132200/132172-61-3.png)
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![2,2′-Methylenebis[(4S)-4-tert-butyl-2-oxazoline]](/data/chemimg/106700/132098-54-5.png)
![2,2′-Methylenebis[(4S)-4-tert-butyl-2-oxazoline]](/data/chemimg/106700/132098-54-5_b.png)
![Aziridine, 2-butyl-1-[(4-methylphenyl)sulfonyl]-](http://img.cochemist.com/ccimg/117000/116905-61-4.png)
![Aziridine, 2-butyl-1-[(4-methylphenyl)sulfonyl]-](http://img.cochemist.com/ccimg/117000/116905-61-4_b.png)
![Phenol, 4-[[(2-aminophenyl)imino]methyl]-](http://img.cochemist.com/ccimg/85600/85573-09-7.png)
![Phenol, 4-[[(2-aminophenyl)imino]methyl]-](http://img.cochemist.com/ccimg/85600/85573-09-7_b.png)
![1,4-Benzenediamine, N1-[4-[(4-aminophenyl)amino]phenyl]-N4-[4-(phenylamino)phenyl]-](/data/chemimg/1332600/80471-62-1.png)
![1,4-Benzenediamine, N1-[4-[(4-aminophenyl)amino]phenyl]-N4-[4-(phenylamino)phenyl]-](/data/chemimg/1332600/80471-62-1_b.png)
![1,4-Benzenediamine, N-(4-aminophenyl)-N'-[4-(phenylamino)phenyl]-](http://img.cochemist.com/ccimg/80500/80471-61-0.png)
![1,4-Benzenediamine, N-(4-aminophenyl)-N'-[4-(phenylamino)phenyl]-](http://img.cochemist.com/ccimg/80500/80471-61-0_b.png)
![7-Azabicyclo[4.1.0]heptane, 7-[(4-methylphenyl)sulfonyl]-](http://img.cochemist.com/ccimg/68900/68820-12-2.png)
![7-Azabicyclo[4.1.0]heptane, 7-[(4-methylphenyl)sulfonyl]-](http://img.cochemist.com/ccimg/68900/68820-12-2_b.png)
![(6E)-6-[1-(2-quinolin-2-ylhydrazino)ethylidene]cyclohexa-2,4-dien-1-one](http://img.cochemist.com/ccimg/59100/59034-56-9.png)
![(6E)-6-[1-(2-quinolin-2-ylhydrazino)ethylidene]cyclohexa-2,4-dien-1-one](http://img.cochemist.com/ccimg/59100/59034-56-9_b.png)
![D-Streptamine,O-2-amino-2,7-dideoxy-D-glycero-a-D-gluco-heptopyranosyl-(1®4)-O-[3-deoxy-4-C-methyl-3-(methylamino)-b-L-arabinopyranosyl-(1®6)]-2-deoxy-](http://img.cochemist.com/ccimg/49900/49863-47-0.png)
![D-Streptamine,O-2-amino-2,7-dideoxy-D-glycero-a-D-gluco-heptopyranosyl-(1®4)-O-[3-deoxy-4-C-methyl-3-(methylamino)-b-L-arabinopyranosyl-(1®6)]-2-deoxy-](http://img.cochemist.com/ccimg/49900/49863-47-0_b.png)
![2,8-dibenzyl-1,3,7,9-tetrahydro-[1,3]benzoxazino[8,7-h][1,3]benzoxazine](http://img.cochemist.com/ccimg/41200/41193-15-1.png)
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![Benzenemethanol, α-[(1R)-1-nitroethyl]-, (αR)-rel-](/data/chemimg/3769800/38316-08-4.png)
![Benzenemethanol, α-[(1R)-1-nitroethyl]-, (αR)-rel-](/data/chemimg/3769800/38316-08-4_b.png)
![2-Oxazolidinone, 3-[(4-methylphenyl)sulfonyl]-5-phenyl-](http://img.cochemist.com/ccimg/34900/34889-55-9.png)
![2-Oxazolidinone, 3-[(4-methylphenyl)sulfonyl]-5-phenyl-](http://img.cochemist.com/ccimg/34900/34889-55-9_b.png)
![b-D-Glucopyranoside,2-[[[(1-hydroxy-6-oxo-2-cyclohexen-1-yl)carbonyl]oxy]methyl]phenyl](http://img.cochemist.com/ccimg/29900/29836-41-7.png)
![b-D-Glucopyranoside,2-[[[(1-hydroxy-6-oxo-2-cyclohexen-1-yl)carbonyl]oxy]methyl]phenyl](http://img.cochemist.com/ccimg/29900/29836-41-7_b.png)
![b-D-Glucopyranoside,2-[[[(1-hydroxy-6-oxo-2-cyclohexen-1-yl)carbonyl]oxy]methyl]phenyl, 2-benzoate](http://img.cochemist.com/ccimg/29900/29836-40-6.png)
![b-D-Glucopyranoside,2-[[[(1-hydroxy-6-oxo-2-cyclohexen-1-yl)carbonyl]oxy]methyl]phenyl, 2-benzoate](http://img.cochemist.com/ccimg/29900/29836-40-6_b.png)
![4-{[2-(2-oxo-2H-indol-3-yl)hydrazino]sulfonyl}benzoic acid](http://img.cochemist.com/ccimg/29600/29519-87-7.png)
![4-{[2-(2-oxo-2H-indol-3-yl)hydrazino]sulfonyl}benzoic acid](http://img.cochemist.com/ccimg/29600/29519-87-7_b.png)
](http://img.cochemist.com/ccimg/27000/26913-06-4.png)
](http://img.cochemist.com/ccimg/27000/26913-06-4_b.png)
![Poly[oxy(1-oxo-1,6-hexanediyl)]](http://img.cochemist.com/ccimg/25300/25248-42-4.png)
![Poly[oxy(1-oxo-1,6-hexanediyl)]](http://img.cochemist.com/ccimg/25300/25248-42-4_b.png)
![Poly[(1,3-dihydro-1,3-dioxo-2H-isoindole-2,5-diyl)carbonyl(1,3-dihydro-1,3-dioxo-2H-isoindole-5,2-diyl)-1,4-phenyleneoxy-1,4-phenylene]](http://img.cochemist.com/ccimg/25000/24991-11-5.png)
![Poly[(1,3-dihydro-1,3-dioxo-2H-isoindole-2,5-diyl)carbonyl(1,3-dihydro-1,3-dioxo-2H-isoindole-5,2-diyl)-1,4-phenyleneoxy-1,4-phenylene]](http://img.cochemist.com/ccimg/25000/24991-11-5_b.png)
![Aziridine,1-[(4-methylphenyl)sulfonyl]-2-phenyl-](http://img.cochemist.com/ccimg/24400/24395-14-0.png)
![Aziridine,1-[(4-methylphenyl)sulfonyl]-2-phenyl-](http://img.cochemist.com/ccimg/24400/24395-14-0_b.png)
![Benzo[2,1-b:3,4-b']dithiophene-4,5-dione](/data/chemimg/1467500/24243-32-1.png)
![Benzo[2,1-b:3,4-b']dithiophene-4,5-dione](/data/chemimg/1467500/24243-32-1_b.png)
![2(1H)-Pyrimidinone,4-amino-1-[5-O-(tricyclo[3.3.1.13,7]dec-1-ylcarbonyl)-b-D-arabinofuranosyl]-](http://img.cochemist.com/ccimg/23200/23113-01-1.png)
![2(1H)-Pyrimidinone,4-amino-1-[5-O-(tricyclo[3.3.1.13,7]dec-1-ylcarbonyl)-b-D-arabinofuranosyl]-](http://img.cochemist.com/ccimg/23200/23113-01-1_b.png)
![21-[6-(methylsulfanyl)-9H-purin-9-yl]pregn-4-ene-3,20-dione](http://img.cochemist.com/ccimg/21200/21170-27-4.png)
![21-[6-(methylsulfanyl)-9H-purin-9-yl]pregn-4-ene-3,20-dione](http://img.cochemist.com/ccimg/21200/21170-27-4_b.png)
![4H-1-Benzopyran-4-one,2-[4-(b-D-glucopyranosyloxy)phenyl]-5,7-dihydroxy-](http://img.cochemist.com/ccimg/20500/20486-34-4.png)
![4H-1-Benzopyran-4-one,2-[4-(b-D-glucopyranosyloxy)phenyl]-5,7-dihydroxy-](http://img.cochemist.com/ccimg/20500/20486-34-4_b.png)
![Ethanone, 1-(4'-ethenyl[1,1'-biphenyl]-4-yl)-](http://img.cochemist.com/ccimg/18600/18594-11-1.png)
![Ethanone, 1-(4'-ethenyl[1,1'-biphenyl]-4-yl)-](http://img.cochemist.com/ccimg/18600/18594-11-1_b.png)
![2-Methyl-2H-benzo[d][1,2,3]triazole](http://img.cochemist.com/ccimg/16600/16584-00-2.png)
![2-Methyl-2H-benzo[d][1,2,3]triazole](http://img.cochemist.com/ccimg/16600/16584-00-2_b.png)
![(4-chlorocyclohex-1-yliumyl)[tris(4-chlorophenyl)]borate(1-)](http://img.cochemist.com/ccimg/14700/14644-80-5.png)
![(4-chlorocyclohex-1-yliumyl)[tris(4-chlorophenyl)]borate(1-)](http://img.cochemist.com/ccimg/14700/14644-80-5_b.png)
![2-({2-[2-{[(6-amino-2-{3-amino-1-[(2,3-diamino-3-oxopropyl)amino]-3-oxopropyl}-5-methylpyrimidin-4-yl)carbonyl]amino}-3-[(5-{[1-({2-[4-({4-[(diaminomethylidene)amino]butyl}carbamoyl)-4',5'-dihydro-2,4'-bi-1,3-thiazol-2'-yl]ethyl}amino)-3-hydroxy-1-oxobuta](http://img.cochemist.com/ccimg/11100/11031-11-1.png)
![2-({2-[2-{[(6-amino-2-{3-amino-1-[(2,3-diamino-3-oxopropyl)amino]-3-oxopropyl}-5-methylpyrimidin-4-yl)carbonyl]amino}-3-[(5-{[1-({2-[4-({4-[(diaminomethylidene)amino]butyl}carbamoyl)-4',5'-dihydro-2,4'-bi-1,3-thiazol-2'-yl]ethyl}amino)-3-hydroxy-1-oxobuta](http://img.cochemist.com/ccimg/11100/11031-11-1_b.png)
![Cyclohexanamine,N-[(2-benzothiazolylthio)methyl]-N-cyclohexyl-](http://img.cochemist.com/ccimg/6400/6323-43-9.png)
![Cyclohexanamine,N-[(2-benzothiazolylthio)methyl]-N-cyclohexyl-](http://img.cochemist.com/ccimg/6400/6323-43-9_b.png)
![(5E)-5-[(4-methylphenyl)hydrazono]-6-oxo-5,6-dihydronaphthalene-2-sulfonic acid](http://img.cochemist.com/ccimg/5900/5859-07-4.png)
![(5E)-5-[(4-methylphenyl)hydrazono]-6-oxo-5,6-dihydronaphthalene-2-sulfonic acid](http://img.cochemist.com/ccimg/5900/5859-07-4_b.png)
![1-(naphthalen-2-yl)-2-[(6-nitro-1,3-benzothiazol-2-yl)sulfanyl]ethanone](http://img.cochemist.com/ccimg/5400/5397-96-6.png)
![1-(naphthalen-2-yl)-2-[(6-nitro-1,3-benzothiazol-2-yl)sulfanyl]ethanone](http://img.cochemist.com/ccimg/5400/5397-96-6_b.png)
![9-Octadecenoic acid(9Z)-,1,1'-[(1R)-1-[[[(2-aminoethoxy)hydroxyphosphinyl]oxy]methyl]-1,2-ethanediyl]ester](http://img.cochemist.com/ccimg/4100/4004-05-1.png)
![9-Octadecenoic acid(9Z)-,1,1'-[(1R)-1-[[[(2-aminoethoxy)hydroxyphosphinyl]oxy]methyl]-1,2-ethanediyl]ester](http://img.cochemist.com/ccimg/4100/4004-05-1_b.png)
![2-(3,4-dihydroxyphenyl)-3,5-dihydroxy-7-[(2s,3r,4s,5s,6r)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxychromen-4-one](http://img.cochemist.com/ccimg/500/491-50-9.png)
![2-(3,4-dihydroxyphenyl)-3,5-dihydroxy-7-[(2s,3r,4s,5s,6r)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxychromen-4-one](http://img.cochemist.com/ccimg/500/491-50-9_b.png)
![2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-3-[(2R,3S,4R,5S,6S)-3,4,5-trihydroxy-6-(hydroxymethyl)tetrahydropyran-2-yl]oxy-chromen-4-one](http://img.cochemist.com/ccimg/500/482-35-9.png)
![2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-3-[(2R,3S,4R,5S,6S)-3,4,5-trihydroxy-6-(hydroxymethyl)tetrahydropyran-2-yl]oxy-chromen-4-one](http://img.cochemist.com/ccimg/500/482-35-9_b.png)
![5,7-dihydroxy-2-(4-hydroxyphenyl)-3-[(2s,3r,4s,5s,6r)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxychromen-4-one](http://img.cochemist.com/ccimg/500/480-10-4.png)
![5,7-dihydroxy-2-(4-hydroxyphenyl)-3-[(2s,3r,4s,5s,6r)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxychromen-4-one](http://img.cochemist.com/ccimg/500/480-10-4_b.png)
![6H-Indolo[3,2,1-de][1,5]naphthyridin-6-one](http://img.cochemist.com/ccimg/500/479-43-6.png)
![6H-Indolo[3,2,1-de][1,5]naphthyridin-6-one](http://img.cochemist.com/ccimg/500/479-43-6_b.png)
![L-Phenylalanine,N-[[(3R)-5-chloro-3,4-dihydro-8-hydroxy-3-methyl-1-oxo-1H-2-benzopyran-7-yl]carbonyl]-](http://img.cochemist.com/ccimg/400/303-47-9.png)
![L-Phenylalanine,N-[[(3R)-5-chloro-3,4-dihydro-8-hydroxy-3-methyl-1-oxo-1H-2-benzopyran-7-yl]carbonyl]-](http://img.cochemist.com/ccimg/400/303-47-9_b.png)
![Pyridine, 2-[4-[2-(5-ethynyl-2-methyl-3-thienyl)-3,3,4,4,5,5-hexafluoro-1-cyclopenten-1-yl]-5-methyl-2-thienyl]-](/data/chemimg/154300/1399843-16-3.png)
![Pyridine, 2-[4-[2-(5-ethynyl-2-methyl-3-thienyl)-3,3,4,4,5,5-hexafluoro-1-cyclopenten-1-yl]-5-methyl-2-thienyl]-](/data/chemimg/154300/1399843-16-3_b.png)
![Pyridine, 2-[4-[3,3,4,4,5,5-hexafluoro-2-[2-methyl-5-[2-(trimethylsilyl)ethynyl]-3-thienyl]-1-cyclopenten-1-yl]-5-methyl-2-thienyl]-](/data/chemimg/154300/1399843-15-2.png)
![Pyridine, 2-[4-[3,3,4,4,5,5-hexafluoro-2-[2-methyl-5-[2-(trimethylsilyl)ethynyl]-3-thienyl]-1-cyclopenten-1-yl]-5-methyl-2-thienyl]-](/data/chemimg/154300/1399843-15-2_b.png)
![1-Propanaminium,N,N,N-trimethyl-2,3-bis[[(9Z)-1-oxo-9-octadecen-1-yl]oxy]-](http://img.cochemist.com/ccimg/113700/113669-21-9.png)
![1-Propanaminium,N,N,N-trimethyl-2,3-bis[[(9Z)-1-oxo-9-octadecen-1-yl]oxy]-](http://img.cochemist.com/ccimg/113700/113669-21-9_b.png)
![7-bromo-2,3-diphenyl-Pyrido[2,3-b]pyrazine](http://img.cochemist.com/ccimg/38900/38870-31-4.png)
![7-bromo-2,3-diphenyl-Pyrido[2,3-b]pyrazine](http://img.cochemist.com/ccimg/38900/38870-31-4_b.png)
![1-[4-(3-METHYL-BUTOXY)-PHENYL]-ETHANONE](http://img.cochemist.com/ccimg/30300/30237-26-4.png)
![1-[4-(3-METHYL-BUTOXY)-PHENYL]-ETHANONE](http://img.cochemist.com/ccimg/30300/30237-26-4_b.png)
![8-[3-(2-chlorophenothiazin-10-yl)propyl]-1-thia-4,8-diazaspiro[4.5]decan-3-one](http://img.cochemist.com/ccimg/24600/24527-27-3.png)
![8-[3-(2-chlorophenothiazin-10-yl)propyl]-1-thia-4,8-diazaspiro[4.5]decan-3-one](http://img.cochemist.com/ccimg/24600/24527-27-3_b.png)
![4-tert-butyl-2-[(cyclohexylamino)methyl]-6-methylphenol](http://img.cochemist.com/ccimg/6700/6640-90-0.png)
![4-tert-butyl-2-[(cyclohexylamino)methyl]-6-methylphenol](http://img.cochemist.com/ccimg/6700/6640-90-0_b.png)
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