Co-reporter:Rui-Yang Wang, Shu-Fen Zou, Bai-Yu Jiang, Bin Fan, Meng-Fei Hou, Biao Zuo, Xin-Ping Wang, Jun-Ting Xu, and Zhi-Qiang Fan
Crystal Growth & Design November 1, 2017 Volume 17(Issue 11) pp:5908-5908
Publication Date(Web):October 2, 2017
DOI:10.1021/acs.cgd.7b01016
Concomitant double crystallization processes widely occur in semicrystalline polymers and their blends because of structural and morphological heterogeneity. In this work, a generalized kinetics model was established for the isothermal crystallization in the presence of concomitant double crystallization processes, based on the Avrami theory for single crystallization process. The different situations of the double crystallization processes, including independent, competitive, and composite types, are considered in the model by introducing the concept of “domains”. This model was applied to crystallization of triblock terpolymer with morphological defects, polymorphic poly(vinylidene fluoride)/nanoclay nanocomposite, isotactic polypropylene with a broad isotacticity distribution, and poly(ethylene terephthalate) ultrathin film. It is found that, besides the information on crystallization kinetics, other information such as morphological defect, nucleation density, cocrystallization, and structure of ultrathin film can also be provided by this model.
Co-reporter:Jun-Huan Li, Yilin Li, Jun-Ting Xu, and Christine K. Luscombe
ACS Applied Materials & Interfaces May 31, 2017 Volume 9(Issue 21) pp:17942-17942
Publication Date(Web):May 9, 2017
DOI:10.1021/acsami.7b03074
Due to their low cost and high efficiency, polymer/nanocrystal hybrid solar cells (HSCs) have attracted much attention in recent years. In this work, water-soluble hybrid materials consisting of amphiphilic block copolymers (ABCPs) and cadmium telluride nanocrystals (CdTe NCs) were used as the active layer to fabricate the HSCs via aqueous processing. The ABCPs composed of poly(3-hexylthiophene) (P3HT) and poly(acrylic acid) (PAA) self-assembled into ordered nanostructured micelles which then transformed to nanowires by comicellization with P3HT additives. Furthermore, after annealing, the hybrid materials formed an interpenetrating network which resulted in a maximum power conversion efficiency of 4.8% in the HSCs. The properties of the hybrid materials and the film morphology were studied and correlated to the device performance. The results illustrate how the inclusion of ABCPs for directed assembly and homo-P3HT for charge transport and light absorption improves device performance. The aqueous-processed HSCs based on the ABCPs and NCs offer an effective method for the fabrication of efficient solar cells.Keywords: amphiphilic block copolymer; aqueous-processed; hybrid; self-assembled; solar cells;
Co-reporter:Ping Li, Jun-Huan Li, Bin Fan, Jun-Ting Xu, Zhi-Qiang Fan
Composites Science and Technology 2017 Volume 148(Volume 148) pp:
Publication Date(Web):18 August 2017
DOI:10.1016/j.compscitech.2017.05.015
In the present work, carbon nanotubes (CNTs)-induced solution crystallization of N, N′-dioctyl perylene tetracarboxylic diimide (PTCDI-C8) in o-dichlorobenzene was studied. It is found that the nanohybrid shish-kebab (NHSK) supramolecular structure, wherein the single-walled carbon nanotubes (SWCNTs) serve as the shish and PTCDI-C8 crystals are the kebabs, with regular arrangement of the kebabs can be formed. UV–vis, photoluminescence spectroscopy and XPS studies reveal that there exist strong π-π interaction between PTCDI-C8 and SWCNTs, and some PTCDI-C8 molecules are already adsorbed on SWCNTs surface prior to crystallization. This is the first example of NHSK structure formed by CNTs and organic small molecules. Nevertheless, multi-walled carbon nanotubes (MWCNTs) cannot induce PTCDI-C8 to form NHSK structure under the same conditions. This indicates that geometric confinement may be the predominant factor affecting the orientation of the pre-adsorbed PTCDI-C8 molecules and epitaxial growth of the crystals.Download high-res image (154KB)Download full-size image
Co-reporter:Jun-Huan Li;Yuyin Xi;Lilo D. Pozzo;Christine K. Luscombe
Journal of Materials Chemistry C 2017 vol. 5(Issue 21) pp:5128-5134
Publication Date(Web):2017/06/01
DOI:10.1039/C7TC01419H
The nanoscale structure and macroscopic morphology of π-conjugated polymers are very important for their electronic application. While ordered single crystals of small molecules have been obtained via solution deposition, macroscopically aligned films of π-conjugated polymers deposited directly from solution have always required surface modification or complex pre-deposition processing of the solution. Here, ordered nanowires were obtained via shear-enhanced crystallization of π-conjugated polymers at the air–liquid–solid interface using simple deposition of the polymer solution onto an inclined substrate. The formation of macroscopically aligned nanowire arrays was found to be due to the synergy between intrinsic (π-conjugated backbone) and external (crystallization conditions) effects. The oriented nanowires showed remarkable improvement in the charge carrier mobility compared to spin-coated films as characterized in organic field-effect transistors (OFETs). Considering the simplicity and large-scale applicability, shear-enhanced crystallization of π-conjugated polymers provides a promising strategy to achieve high-performance polymer semiconductor films for electronics applications.
Co-reporter:Rui-Yang Wang, Xiang-Yue Wang, Bin Fan, Jun-Ting Xu, Zhi-Qiang Fan
Polymer 2017 Volume 117(Volume 117) pp:
Publication Date(Web):19 May 2017
DOI:10.1016/j.polymer.2017.04.024
•Microphase separation and crystallization behaviors of bi-phased triblock terpolymers were studied.•The competitive dissolution of the middle block leads to shift of the phase boundaries.•Break-out crystallization occurs more easily due to the competitive dissolution of the middle block.A series of poly(ε-caprolactone)-b-poly(n-butyl acrylate)-b-polystyrene (PCL-b-PnBA-b-PS) triblock terpolymers with fixed PCL and PnBA block lengths but different PS block lengths were prepared. In all of these triblock terpolymers the PnBA block can be competitively dissolved in both the PCL and PS phases to form bi-phase structures in the melt, as revealed by atomic force microscopy (AFM). Due to the “competitive dissolution effect” of the PnBA middle block, the microphase separation and crystallization behaviors of these triblock terpolymers are different from those of common diblock copolymers to some extent. As revealed by the Flory-Huggins parameters, more PnBA segments tend to dissolved in the PS phase. Therefore, the volume fraction of the PS-rich phase (fPS-rich) is evidently larger than the calculated volume fraction of the PS block (fPS), and the phase boundaries between two different structures shift to lower fPS. There also exists a thick interphase layer between the PS-rich and PCL-rich phases due to competitive dissolution of the PnBA block. However, confined crystallization can only occur at a larger fPS-rich, though the measured glass transition temperature (Tg) is high for the PS block. This can be attributed to a high fraction of the soft zone surrounding the PCL-rich phase and the lower volume fraction of the hard zone.Download high-res image (79KB)Download full-size image
Co-reporter:Zaizai Tong, Junyi Zhou, Rui-Yang Wang, Jun-Ting Xu
Polymer 2017 Volume 130(Volume 130) pp:
Publication Date(Web):9 November 2017
DOI:10.1016/j.polymer.2017.09.071
•A series of crystalline/liquid crystalline block copolymers (PMMAzo-b-PLLA) with well-defined structure were synthesized.•The interplay of microphase separation, crystallization and LC ordering in these crystalline/LC BCPs were investigated.•PLLA crystallization can stabilize the liquid crystalline structure, leading to an enhanced LC ordering.•Under suitable conditions, the LC ordering can induce formation of PLLA ε-crystals in the bulk.A series of liquid crystalline/crystalline block copolymers (BCPs) containing poly(methacrylate) block with liquid crystalline (LC) azobenzene moieties in the side chains (PMMAzo) and crystalline block poly(l-lactide) (PLLA) were prepared. The interplay of microphase separation, crystallization and LC ordering in these BCPs was investigated. It is revealed that microphase separation between two blocks is favorable to the LC ordering, which is attributed to the enhanced local concentration of LC moieties in PMMAzo microdomains. For a similar reason, crystallization of PLLA can intensify microphase separation thus facilitate LC ordering of PMMAzo. PLLA crystallization may also stabilize the LC structure, leading to phase transition temperatures of the BCPs higher than that of PMMAzo homopolymer. On the other hand, the LC ordering can conversely affect crystallization of PLLA. The crystallizability of PLLA is weakened by the chemically linked PMMAzo block. The special PLLA ε-crystals, which are usually formed in the presence of organic solvents, are unexpectedly observed under suitable conditions.Download high-res image (203KB)Download full-size image
Co-reporter:Bing Zhou, Jun-Ting Xu, Zhi-Qiang Fan
Composites Science and Technology 2016 Volume 132() pp:24-30
Publication Date(Web):23 August 2016
DOI:10.1016/j.compscitech.2016.06.009
In the present work, the nucleation mechanism for crystallization of poly(ε-caprolactone)s grafted on multi-walled carbon nanotubes (MWCNTs-g-PCLs), in which the PCL chains are structurally confined, was studied using self-nucleation method and the effects of the molecular weight and grafting density were investigated. It is found that the structural confinement reduces the nucleation activity of the self-nuclei but enhances the interaction between MWCNTs and PCL chains, leading to a narrower self-nucleation domain (DII) or even disappearance of DII. The PCL chains are more stretched at a larger grafting density and higher molecular weight of PCL, which facilitates formation of self-nuclei but also increases the nucleation activity of MWCNTs. The nucleation activity of MWCNTs may be enhanced at a higher grafting density as well. The values of nucleation efficiency of MWCNTs in the blend and MWCNTs-g-PCLs were also evaluated. Higher nucleation efficiency is observed for the MWCNTs-g-PCL with shorter PCL chains but higher grafting density.
Co-reporter:Bin Fan, Lei Liu, Jun-Huan Li, Xi-Xian Ke, Jun-Ting Xu, Bin-Yang Du and Zhi-Qiang Fan
Soft Matter 2016 vol. 12(Issue 1) pp:67-76
Publication Date(Web):28 Sep 2015
DOI:10.1039/C5SM02226F
Crystallization-driven self-assembly of polyethylene-b-poly(tert-butylacrylate) (PE-b-PtBA) block copolymers (BCPs) in N,N-dimethyl formamide (DMF) was studied. It is found that all three PE-b-PtBA BCPs used in this work can self-assemble into one-dimensional crystalline cylindrical micelles. When the BCP solution is cooled to crystallization temperature (Tc) from 130 °C, the seed micelles may be produced via two competitive processes in the initial period: stepwise micellization/crystallization and simultaneous crystallization/micellization. Subsequently, the seed micelles can undergo growth driven by the epitaxial crystallization of the unimers. The lengths of both the seed micelles and the grown micelles are longer for the BCP with a longer PtBA block at a higher Tc. Quasi-living growth of the PE-b-PtBA crystalline cylindrical micelles is achieved at a higher Tc. A longer PtBA block evidently retards the attachment of unimers to the crystalline micelles, leading to a slower growth rate.
Co-reporter:Shao-Fei Song, Yin-Tian Guo, Rui-Yang Wang, Zhi-Sheng Fu, Jun-Ting Xu, and Zhi-Qiang Fan
Macromolecules 2016 Volume 49(Issue 16) pp:6001-6011
Publication Date(Web):August 5, 2016
DOI:10.1021/acs.macromol.6b01324
A new series of polyethylene (PE) containing arylene ether units as defects in the main chain, which were precisely separated by 20 CH2 units, were synthesized via acyclic diene metathesis (ADMET) polymerization. The thermal stability, crystallization, and melting behaviors, crystal structure, and chain stacking were investigated with TGA, DSC, WAXD, and SAXS. It is found that the substitution position in the arylene units has a remarkable influence on the chain stacking and their location in the solid phase. The ortho-substituted phenylene units are excluded from the crystal phase, leading to a low melting temperature (Tm). In contrast, the para-substituted phenylene units can be included into the crystal, leading to a high Tm. The meta-substituted phenylene units can be partially included into the crystal, resulting in mixed crystal structures and an intermediate Tm. Such an effect of substitution position in precision PEs is different from that in poly(ethylene oxide) reported in the literature, which can be ascribed to the matchable configuration of the defects in the main chain with the conformation of PE in the crystals. When the defects become naphthylene ether units, the crystallization and melting behaviors of the polymers are similar to or different from those of the precision PEs with phenylene ether defects, depending on the substitution position. This shows that both the substitution position in the arylene ether defects and the defect size exert effects on crystallization, melting behaviors, and chain stacking of precision PEs.
Co-reporter:Jie-Xin Yang, Bin Fan, Jun-Huan Li, Jun-Ting Xu, Bin-Yang Du, and Zhi-Qiang Fan
Macromolecules 2016 Volume 49(Issue 1) pp:367-372
Publication Date(Web):December 24, 2015
DOI:10.1021/acs.macromol.5b02349
Two hydrogen (H)-bond donors, phenol and l-threonine, were added into the aqueous solutions containing crystalline micelles of a poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) block copolymer, respectively. Dynamic light scattering (DLS) characterization showed that the micellar size became smaller after addition of phenol. Transmission electron microscopy (TEM) results revealed that the long crystalline cylindrical micelles formed in the neat aqueous solution were fragmented into short cylinders and even quasi-spherical micelles, as the phenol concentration increased. By contrast, the spherical PCL-b-PEO crystalline micelles could be transformed into short cylinders and then long cylinders after addition of l-threonine. Reversible morphological transformation was realized for the PCL-b-PEO crystalline micelles by adding these two H-bond donors alternately. It is confirmed that both phenol and l-threonine could form H-bonds with PEO. We proposed that, the micellar corona was swollen by phenol, leading to fragmentation of the micellar core, whereas the PEO blocks in the micellar corona was dynamically cross-linked by l-threonine beacuse of its multiple H-bond-donation groups, resulting in a smaller reduced tethering density.
Co-reporter:Jie Huang, Rui-Yang Wang, Jun-Ting Xu, Zhi-Qiang Fan
Polymer 2016 Volume 99() pp:332-339
Publication Date(Web):2 September 2016
DOI:10.1016/j.polymer.2016.07.045
•H-bonding interaction was introduced into block copolymers to compete with microphase separation.•The inverse order-to-order transition was achieved.•The effect of chain conformation induced by H-bonds on microphase separation was revealed.Hydrogen (H)-bonding interaction was introduced into a poly(ethylene oxide)-b-poly(tert-butyl acrylate) (PEO-b-PtBA) block copolymer (BCP) by partial hydrolysis of tBA units into acrylic acid (AA) ones, in order to compete with the segregation force between the PEO and PtBA blocks. It was found that, as the hydrolysis degree (Dhyd) of the PtBA block increased, the structure of the PEO-b-P(tBA-co-AA) BCPs underwent the change from hexagonally packed cylindrical (HEX) into body-centered cubic spherical (BCC), then into HEX. The first HEX-to-BCC transition at lower Dhyd arose from the enhanced compatibility between the PEO and P(tBA-co-AA) blocks induced by the H-bonding interaction. When a PEO-b-P(tBA-co-AA) BCP with a HEX structure was heated, the BCC-to-HEX order-order transition (OOT), which was opposed to that in the common BCPs with an upper critical ordering temperature (UCOT) phase diagram, could be achieved because the H-bonding interaction was weakened at higher temperature. The second BCC-to-HEX at higher Dhyd was interpreted in terms of the enhanced chain rigidity and the chain arrangement approximately parallel to the microdomain interface induced by H-bonding interaction. The variation of the H-bonding interaction with temperature and the conformational change of the PEO block induced by H-bonding interaction were verified with FT-IR.
Co-reporter:Jun-Huan Li, Ping Li, Jun-Ting Xu, Christine K. Luscombe, and Zhi-Qiang Fan
The Journal of Physical Chemistry C 2016 Volume 120(Issue 48) pp:27665-27674
Publication Date(Web):November 17, 2016
DOI:10.1021/acs.jpcc.6b09691
The straightened morphology of single-walled carbon nanotubes (SWCNTs) driven by rigid and conjugated regioregular poly(3-hexylthiophene) (rr-P3HT) and the related mechanism were studied with transmission electron microscopy (TEM), atomic force microscopy (AFM), and spectroscopic methods. It was found that bent SWCNTs could be straightened significantly in solutions with low SWCNT concentration, which was quantitatively confirmed by the increased persistence length. UV–vis and photoluminescence spectroscopic studies revealed that there exists strong π–π interaction between P3HT chains and SWCNTs. The P3HT chains also became more rigid after interaction with SWCNTs. We proposed that SWCNTs were straightened by the coaxially adsorbed P3HT chains instead of epitaxial P3HT crystals. Multiwalled carbon nanotubes (MWCNTs) could not be straightened by P3HT under the same conditions, showing that the straightening force was limited. This result may be useful in preparation of aligned arrays of SWCNTs/conjugated polymer supramolecular structures.
Co-reporter:Bing Zhou, Jun-Huan Li, Bin Fan, Ping Li, Jun-Ting Xu, and Zhi-Qiang Fan
Crystal Growth & Design 2016 Volume 16(Issue 12) pp:
Publication Date(Web):November 3, 2016
DOI:10.1021/acs.cgd.6b00915
The crystal morphology of poly(ε-caprolactone)/multiwalled carbon nanotube (PCL/MWCNT) blends and MWCNT-g-PCL grafting polymers crystallized in n-hexanol was investigated. Two typical morphologies are observed: a straight and rod-like core–sheath structure with embedded MWCNTs as the core and PCL polycrystals of high crystallinity as the sheath, and a bent double-layer structure with MWCNTs covered by a PCL layer of low crystallinity. It is found that thinner (outer diameter <15 nm) and shorter (length <2 μm) MWCNTs are easier to be straightened by PCL crystals, and the grafted PCL chains have weaker crystallizability due to structural confinement and thus a weaker ability of straightening MWCNTs. Electron diffraction and high-resolution transmission electron microscopy reveal that the PCL crystals are randomly orientated with the b-axis perpendicular to the MWCNT surface. The growth direction of the PCL crystals is not perpendicular to the axis of MWCNT, possibly due to the nucleation effect of the preadsorbed PCL chains in the solution, which helically wrap MWCNTs. This leads to wrapping and straightening of MWCNTs by rigid PCL crystals.
Co-reporter:Zai-Zai Tong, Rui-Yang Wang, Jie Huang, Jun-Ting Xu and Zhi-Qiang Fan
Polymer Chemistry 2015 vol. 6(Issue 12) pp:2214-2225
Publication Date(Web):16 Jan 2015
DOI:10.1039/C5PY00004A
The double hydrophobic azobenzene-containing diblock copolymers, namely, poly(L-lactide)-b-poly[6-(4-(4-methoxyphenylazo)phenoxy)hexyl methacrylate] (PLLA-b-PMMAZO), were successfully prepared by sequential atom transfer radical polymerization (ATRP) and ring opening polymerization. These block copolymers (BCPs) can self-assemble into various morphologies in aqueous solution via host–guest interaction between the azobenzene (azo) groups and methyl-β-cyclodextrin (β-CD). The complexation equilibrium between azo and β-CD can be shifted by changing the length of the hydrophobic PLLA block, the micelle concentration or the β-CD/azo molar ratio; thus the micellar morphology and the size of the PLLA-b-PMMAZO/β-CD complexes are altered. A vesicle-to-sphere-to-entrapped vesicle transition was observed at β-CD/azo = 1 as the PLLA block length increases. In addition, a large β-CD/azo ratio or higher micelle concentration leads to a vesicle-like morphology, while entrapped vesicles tend to be formed at a smaller β-CD/azo ratio or a lower micelle concentration. It is found that prolongation of the UV irradiation time can also induce a vesicle-to-sphere-to-entrapped vesicle transition of the micellar morphology. Such a transition is reversible upon irradiation of visible light. In summary, the self-assembly behavior of PLLA-b-PMMAZO/β-CD complexes can be readily regulated by different methods. Moreover, the complexation between the azo groups and β-CD is inhomogeneous, which is responsible for the formation of entrapped vesicles and the microphase separation in the core of the spherical micelles and entrapped vesicles.
Co-reporter:Zai-Zai Tong, Jin-Qiao Xue, Rui-Yang Wang, Jie Huang, Jun-Ting Xu and Zhi-Qiang Fan
RSC Advances 2015 vol. 5(Issue 6) pp:4030-4040
Publication Date(Web):05 Dec 2014
DOI:10.1039/C4RA12844C
A series of triblock copolymers with liquid crystalline (LC) poly{6-[4-(4-methoxyphenylazo)phenoxy]hexyl methacrylate} (PMMAZO) as the end blocks and rubbery poly(n-butyl acrylate) (PnBA) as the midblock were synthesized. The effect of the interplay between the LC ordering and microphase separation on the hierarchical assembly of the triblock copolymers was studied. It is found that microphase separation at a larger scale can affect the LC ordering at a smaller scale, such as the stacking of the LC moieties, LC temperature and the domain size of the LC phase. On the other hand, alteration of the LC ordering, such as isotropization and smetic-to-nematic transition, may also lead to an order–order transition (OOT) or change in the long period of the microphase-separated structure. UV light can trigger the isomerization of the azobenzene LC moieties, which can be further amplified and exerts an effect on the microphase separation behavior, including the regularity of the microphase-separated structure and the OOT. The triblock copolymers also exhibit light-variable tensile properties. The results reveal that the phase behavior and mechanical properties of this type of triblock copolymer can be readily regulated by light, thus it may be used as smart and functional thermoplastic elastomer.
Co-reporter:Zai-Zai Tong;Jie Huang;Bing Zhou;Zhi-Qiang Fan
Journal of Applied Polymer Science 2015 Volume 132( Issue 14) pp:
Publication Date(Web):
DOI:10.1002/app.41771
ABSTRACT
The self-nucleation behavior of olefinic blocky copolymer (OBC) / organically modified montmorillonite (OMMT) nanocomposites with a novel collapsed clay structure (c-OMMT) was studied and compared with that of the nanocomposites with an intercalated clay structure (OBC/i-OMMT). Their behaviors appear different in three temperature domains, Domain I (DI) in which the polymer is completely melted and only the heterogeneous nuclei are present, Domain II (DII) in which only self-nucleation occurs and Domain III (DIII) where both self-nucleation and annealing take place. As the OMMT loading increases, the boundary temperature of DI and DII (TIII) shifts to lower temperature and DII becomes narrower. For the OBC/c-OMMT nanocomposites, the TIII or TIIII (the boundary temperature of DI and DIII) can be lower than the end melting temperature ( ) and leads to appearance of a subdomain of DI, DI′, in which the self-nuclei of un-melted fragmental crystals exist but the following crystallization is still initiated by c-OMMT. DII may even disappear at high c-OMMT loadings. By contrast, the TIII of the OBC/i-OMMT nanocomposites is always approximate to or higher than the . DII does not disappear and no DI′ is observed for the OBC/i-OMMT nanocomposites. The nucleation efficiency of c-OMMT is also evidently higher than that of i-OMMT. These results verify that the c-OMMT has stronger nucleation ability than i-OMMT at the same OMMT loading. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41771.
Co-reporter:Xi-xian Ke 徐君庭;Bin-yang Du
Chinese Journal of Polymer Science 2015 Volume 33( Issue 7) pp:1038-1047
Publication Date(Web):2015 July
DOI:10.1007/s10118-015-1656-5
The hybrid micelles of polystyrene-b-poly((N-isopropyl acrylamide)-co-(4-vinylbenzyl chloride)) block copolymer (PS-b-P(NIPAM-co-VBC)) with Prussian blue (PB) in the corona were prepared by reaction of pentacyano(4-(dimethylamino)-pyridine)ferrate (Fe-DMAP)-attached PS-b-P(NIPAM-co-VBC) with FeCl3. The formation of the PB framework inside the micelles was verified by UV-Vis, FTIR and TGA. The morphology of the hybrid micelles was studied by TEM and compared with that of the neat and Fe-DMAP-attached PS-b-P(NIPAM-co-VBC). It is found that attachment of Fe-DMAP may change the short rod-like micelles of the neat PS-b-P(NIPAM-co-VBC) into spherical ones and lead to a smaller micelle size. The morphology of the hybrid micelles may be altered or remain unchanged after formation of the PB framework, depending on the chain structure of PS-b-P(NIPAM-co-VBC) and starting concentration. The thermoresponsive behavior of different micelles was studied using DLS. It is observed that attachment of Fe-DMAP can improve the hydrophilicity of the P(NIPAM-co-VBC) block, leading to weaker hysteresis of the micelle size during the heating and cooling cycle. However, the crosslinked PB framework in the micellar corona may result in a more evident hysteresis phenomenon and blur the two-stepwise change of the micellar size with temperature.
Co-reporter:Zai-Zai Tong, Yao Huang, Jun-Ting Xu, Zhi-Sheng Fu, and Zhi-Qiang Fan
The Journal of Physical Chemistry B 2015 Volume 119(Issue 19) pp:6050-6061
Publication Date(Web):April 23, 2015
DOI:10.1021/acs.jpcb.5b01845
Segmented ethylene-propylene copolymers (SEPs) with different propylene contents were prepared by an unbridged metallocene bis(2,4,6-trimethylindenyl)zirconium dichloride [(2,4,6-Me3Ind)2ZrCl2] catalyst. Due to oscillation of the unbridged ligands in the catalyst, the SEPs are composed of segments with low propylene contents, alternated by the segments with high propylene contents. Such a chain structure was verified by 13C NMR and successive self-nucleation and annealing (SSA). As the propylene/ethylene feed ratio during copolymerization increases, the comonomer contents in both segments are increased, leading to noncrystallizability of the high propylene segments and smaller crystallinity of the low propylene segments. Consequently, SEPs may be used as thermoplastic elastomers (TPEs). The aggregation state structures at nano- and micro-scales were characterized with small angle X-ray scattering, transmission electron microscopy and polarized optical microscopy, and compared with those of ethylene–octene multiblocky copolymers (OBCs) with similar crystallinity. It is found that SEPs form thinner lamellar crystals with a lower melting temperature due to shorter length and higher comonomer content of the low propylene segments. Moreover, the short length of the high propylene segments in SEPs results in an evidently thinner amorphous layer among the lamellar crystals, thus lots of amorphous phases are excluded out of the interlamellae. Accordingly, ill-developed spherulites or even bundle crystals are formed in SEPs, as compared with the well-developed spherulites in OBCs. SEPs exhibit the tensile property of typical TPEs with diffused yielding and large strain at break.
Co-reporter:Xi-Xian Ke, Lian Wang, Jun-Ting Xu, Bin-Yang Du, Ying-Feng Tu and Zhi-Qiang Fan
Soft Matter 2014 vol. 10(Issue 28) pp:5201-5211
Publication Date(Web):16 May 2014
DOI:10.1039/C4SM00698D
The effect of temperature on the micellar morphology of two polystyrene-b-poly(N-isopropylacrylamide) (PS-b-PNIPAM) diblock copolymers in an aqueous solution was investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM). At 25 °C, a mixture of vesicles and spheres are observed for the micelles of PS65-b-PNIPAM108, while PS65-b-PNIPAM360 exhibits mixed cylindrical and spherical micellar morphology. Upon increasing the temperature, the micellar morphology becomes spherical for PS65-b-PNIPAM108 at 60 °C and for PS65-b-PNIPAM360 at 40 °C. Such vesicle-to-sphere and cylinder-to-sphere transitions of micellar morphology are reversible when the micellar solutions are cooled back to 25 °C. However, these temperature-induced morphological transitions of the PS-b-PNIPAM micelles are contrary to the theoretical prediction. Qualitative analysis of the free energy shows that vesicular or cylindrical micelles tend to form at higher temperatures if only the overall volume change of the PNIPAM block is considered. The contradiction between the experimental results and theoretical prediction is interpreted in terms of the local deformability of the PNIPAM chains. At elevated temperatures, the collapsed PNIPAM globules are less deformable and must occupy larger areas at the micellar interface, although the overall volume is smaller at higher temperatures. This will lead to a larger repulsion between the PNIPAM globules and a remarkable increase in the free energy of the corona; thus, the formation of vesicles or cylinders at higher temperatures is prohibited.
Co-reporter:Zai-Zai Tong, Bing Zhou, Jie Huang, Jun-Ting Xu and Zhi-Qiang Fan
RSC Advances 2014 vol. 4(Issue 30) pp:15678-15688
Publication Date(Web):18 Mar 2014
DOI:10.1039/C4RA00628C
The hierarchical structures of olefinic blocky copolymer (OBC)/organically modified montmorillonite (OMMT) nanocomposites with different dispersion states of clay, including collapsed and intercalated OMMT (c-OMMT and i-OMMT), were characterized by various techniques. It is observed that, there are more densely stacked clay layers in single clay particles with a smaller size but larger distance between the adjacent clay particles in OBC/c-OMMT. c-OMMT exhibits stronger nucleation ability on crystallization of OBC than i-OMMT. This leads to a smaller size of the macroscopic crystals, thicker lamellar crystals, and more amorphous phase included in the inter-lamellae but less amorphous phase among different macroscopic crystals in OBC/c-OMMT. These differences in the hierarchical structure are responsible for the more obvious strain-hardening behavior but smaller strain at break of the OBC/c-OMMT nanocomposites.
Co-reporter:Yi-Min Liu;Zai-Zai Tong;Zhi-Sheng Fu ;Zhi-Qiang Fan
Journal of Applied Polymer Science 2014 Volume 131( Issue 18) pp:
Publication Date(Web):
DOI:10.1002/app.40753
ABSTRACT
In this work, we reported calcium tetrahydrophthalate as a high efficient β-nucleating agent (β-NA) for impact-resistant polypropylene copolymer (IPC). The relative fraction of the β-crystal can reach as high as 93.5% when only 0.03% β-NA is added. The non-isothermal and isothermal crystallization behaviors, morphology, lamellar structure and mechanical properties of IPCs with various β-NA contents were studied. During non-isothermal crystallization, the cooling rate has an important influence on the relative fraction of the β-crystal, which decreases remarkably as the cooling rate increases. The β-NA also greatly accelerates crystallization rate of IPC, resulting from both more crystal nuclei and larger Avrami exponent. The small angle X-ray scattering characterization shows that more amorphous components are included into the inter-lamellae after addition of β-NA. Dynamical mechanical analysis (DMA) reveals that the storage modulus at low temperature and the loss factor above 0 °C from the PP component can be enhanced upon addition of β-NA and reach a maximum at the β-NA content of 0.05 wt %. Impact test shows that the impact strength of the IPC at 0°C can be improved as much as 40% when the content of calcium tetrahydrophthalate is 0.10 wt %. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40753.
Co-reporter:Jie-xin Yang;Wei-na He 徐君庭;Bin-yang Du
Chinese Journal of Polymer Science 2014 Volume 32( Issue 9) pp:1128-1138
Publication Date(Web):2014 September
DOI:10.1007/s10118-014-1512-z
Different inorganic salts, including NaSCN, NaCl, MgCl2 and Na2SO4, were added into the aqueous solution containing poly(ɛ-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) semicrystalline micelles. The effects of inorganic salt on the micellar size and morphology were investigated with TEM and DLS. It is found that addition of NaSCN leads to increase of the micellar size, but the micelles remain to be spherical. By contrast, the other three inorganic salts can induce sphere-to-cylinder or sphere-to-lamella transformations of the PCL-b-PEO semicrystalline micelles. The alteration rate of the micellar size with the time after addition of the inorganic salts decreases in the following order: Na2SO4 > NaCl ≈ MgCl2 > NaSCN. These results were interpreted in terms of the “salting-out” ability of the cations and anions. The anions SO42− and Cl− have a stronger “salting-out” ability, driving the morphological transformations of the micelles and leading to a rapid change in micellar size. By contrast, SCN− has a weaker salting-out” ability. The cations Na+ and Mg2+ may associate with the PEO blocks, leading to a “salting-out” effect as well. However, the “salting-out” ability of cations is weaker than that of SO42− and Cl− anions, and the “salting-out” abilities of Na+ and Mg2+ are similar.
Co-reporter:Jie Huang, Rui-Yang Wang, Zai-Zai Tong, Jun-Ting Xu, and Zhi-Qiang Fan
Macromolecules 2014 Volume 47(Issue 23) pp:8359-8367
Publication Date(Web):November 24, 2014
DOI:10.1021/ma502057q
The microphase separation behavior of the hybrids of poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) with different inorganic salts at various doping ratios (r) was studied by temperature-variable SAXS. It was observed that the salts could induce microphase separation to form ordered structure in the originally miscible melt of PCL-b-PEO. The effects of the metal ion and anion were correlated with the competitive interactions of PEO/salt and PCL/salt, which were characterized by FT-IR and DSC, respectively. It was found that at lower doping ratios the salts preferentially interacted with PEO. The larger association number of the metal ion and stronger association between PEO and salt led to a lower onset doping ratio for formation of ordered structure (r0). At higher doping ratios the salt interacted with PCL as well. When the metal ion exhibited a highly selective interaction toward PEO, a more ordered structure with a higher order–order transition temperature (TODT) tended to be formed. The anion in the salt also affected the interactions of PEO/salt and PCL/salt. Weaker Lewis basicity of the anion would result in a stronger interaction of PEO/salt and thus a lower r0. The results showed that the microphase separation behavior of the PCL-b-PEO/salt hybrids was sensitive to the competitive interactions of the salt with the PCL and PEO blocks.
Co-reporter:Jie Huang, Zai-Zai Tong, Bing Zhou, Jun-Ting Xu, Zhi-Qiang Fan
Polymer 2014 Volume 55(Issue 4) pp:1070-1077
Publication Date(Web):25 February 2014
DOI:10.1016/j.polymer.2014.01.012
The phase behavior of a series of LiClO4-doped poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) was studied as a function of PEO volume fraction (fPEO), doping ratio (r) and temperature (T). It is found that the morphology of the hybrids changes from disordered structure (DIS) to hexagonally packed cylindrical (HEX) structure and then to lamellar (LAM) structure as the volume fraction of the PEO/salt phase (fPEO/salt) increases at fPEO/salt < 0.5. Order–order transitions are observed upon heating some hybrids. An approximate phase diagram of the PCL-b-PEO/LiClO4 hybrids with fPEO/salt < 0.5 was constructed in terms of fPEO/salt and the segregation strength (χeffN). As compared with the phase diagram of the weakly segregated diblock copolymers, the phase diagram of the hybrids has two features: the boundaries of the LAM and HEX structures shifts to lower fPEO/salt and body-centered cubic spherical (BCC) structure is not observed for the samples studied. This can be attributed to the weaker ability of the salt inducing microphase separation at low fPEO and the conformational change of the PEO block induced by the salt. Some unexpected phase behaviors were observed for the hybrids with fPEO/salt > 0.5, including the hexagonally perforated layers (HPL) to LAM transition upon heating the same hybrid and HEX to gyroid (GYR) transition with the increase of doping ratio at the same temperature. These unexpected phase behaviors are qualitatively interpreted based on the competitive association of the PCL block with Li+ ions at elevated temperatures and higher doping ratios, which leads to re-distribution of the Li+ ions in different phases and the inconsistency between the calculated fPEO/salt and the real volume fraction of the PEO/salt phase.
Co-reporter:Zai-Zai Tong, Bing Zhou, Jie Huang, Jun-Ting Xu, and Zhi-Qiang Fan
Macromolecules 2014 Volume 47(Issue 1) pp:333-346
Publication Date(Web):January 2, 2014
DOI:10.1021/ma4023263
Two olefinic blocky copolymers (OBCs) were quenched from different mixing states in the melt, and crystallization kinetics and morphology at various crystallization temperatures (Tcs) and corresponding mechanical properties were studied. It is observed that, at lower Tcs, premesophase separation in the melt accelerates crystallization of OBC-A with a weak segregation strength and a larger fraction of the crystalline hard blocks due to enrichment of the hard blocks in the hard-block-rich domains. By contrast, premesophase separation retards crystallization of OBC-B with a stronger segregation strength and lower fraction of the hard blocks because of the prevailing confinement effect at lower Tcs. Moreover, since the hard blocks dissolved in the soft-block-rich domains can crystallize at lower Tcs, which can bridge the crystals formed in different hard-block-rich domains, the crystal growth is not restricted. At higher Tcs, OBC-A crystallizes more slowly from the premesophase-separated melt than that from the homogeneous melt, which is attributed to the weaker crystallizability of the hard blocks dissolved in the soft-block-rich domains and thus the restricted crystal growth. Nevertheless, mesophase separation always takes place prior to crystallization at higher Tcs for OBC-B because of the faster rate of mesophase separation. Therefore, the mixing state in the melt has little effect on crystallization and morphology of OBC-B at higher Tcs. It is found that the mechanical properties of OBCs can be regulated in a wide range by alteration of crystallization conditions. Better mechanical properties can be achieved when OBCs crystallize from the homogeneous melt and at a lower Tc.
Co-reporter:Bing Zhou, Zai-Zai Tong, Jie Huang, Jun-Ting Xu and Zhi-Qiang Fan
CrystEngComm 2013 vol. 15(Issue 38) pp:7824-7832
Publication Date(Web):31 Jul 2013
DOI:10.1039/C3CE40606G
The isothermal crystallization kinetics of poly(ε-caprolactone) (PCL) grafted on multi-walled carbon nanotubes (MWNTs-g-PCL) with high grafting degrees were studied and compared with those of neat PCL and a PCL/MWNTs blend. The Avrami exponent n altered from 3.0 for the neat PCL to nearly 2.0 for the grafting polymers. The grafting polymers exhibit a significantly faster crystallization rate but lower crystallinity than the neat PCL and PCL/MWNTs blend. In the grafting polymers, MWNTs exert both stronger nucleation and confinement effects on the crystallization of PCL than those for the PCL/MWNTs blend. The grafting density affects crystallization of PCL more severely than the molecular weight of the grafting PCL. The crystallization activation energy of the grafting polymers is smaller than that of the PCL/MWNTs blend but larger than that of the neat PCL. The grafted PCL chains are over-crowded and highly stretched, and the PCL crystals lie on the surface of MWNTs with the b-axis basically perpendicular to the surface.
Co-reporter:Yi-Min Liu, Zai-Zai Tong, Jie Huang, Bing Zhou, Jun-Ting Xu, Zhi-Sheng Fu, and Zhi-Qiang Fan
Industrial & Engineering Chemistry Research 2013 Volume 52(Issue 46) pp:16239-16246
Publication Date(Web):2017-2-22
DOI:10.1021/ie402711f
The low molecular weight ethylene–propylene random copolymer (LEPR) in a polypropylene (PP)/EPR in-reactor alloy is replaced by high molecular weight EPR (HEPR). It is found that the phase separation rate of PP/HEPR alloy is much slower than that of PP/LEPR alloy. The effect of phase separation on the crystallization kinetics of PP/HEPR alloy is studied and compared with that of PP/LEPR alloy. The pre-phase-separated PP/HEPR alloy exhibits a faster spherulitic growth rate and overall crystallization rate, as compared with the directly quenched one. This is contrary to the PP/LEPR alloy and is interpreted in terms of the relative rate of crystallization and phase separation based on phase diagram. It is also observed that directly quenched PP/HEPR alloy has a larger long period after crystallization. This can be attributed to more inclusion of EPR-rich phase into inter-lamellae, which is advantageous to the mechanical properties.
Co-reporter:Zai-Zai Tong;Jie Huang;Bing Zhou;Zhi-Qiang Fan
Macromolecular Chemistry and Physics 2013 Volume 214( Issue 5) pp:605-616
Publication Date(Web):
DOI:10.1002/macp.201200615
Abstract
The chain microstructure, crystallization, and morphology of three olefinic blocky copolymers (OBCs) are compared. The weight percentage of the hard block and the octene content in it are calculated from the 13C NMR spectra with a two-site first-order Markovian model. The lengths of the hard blocks are compared from the melting and crystallization behaviors. The remarkable difference between the crystallinity measured by DSC, and wide-angle X-ray diffraction (WAXD) indicates the presence of partially ordered phases. Small angle X-ray scattering (SAXS) shows that the partially ordered phases in OBC-A are mainly located at the interface between the crystalline and amorphous phases, but exist as separated microdomains in OBC-B. As the hard block becomes shorter, there are also more, separated partially ordered phases in OBC-C. Spherulites are observed in all OBCs by POM and the size of the spherulites decreases in the order: OBC-A > OBC-B > OBC-C. TEM shows that spherulites are poorly developed in a thin film of OBC-B.
Co-reporter:Yi-Min Liu;Zhi-Sheng Fu ;Zhi-Qiang Fan
Journal of Applied Polymer Science 2013 Volume 127( Issue 2) pp:1346-1358
Publication Date(Web):
DOI:10.1002/app.37689
Abstract
In the present work, the effect of phase separation on overall isothermal crystallization kinetics of two polypropylene/ethylene-propylene random copolymer (PP/EPR) in-reactor alloys was investigated. It is found that at lower crystallization temperatures (Tc), the overall crystallization rate decreases with increasing phase separation temperature (Ts). This is attributed to the lower linear spherulitic growth rate incurred by the lower PP content in the PP-rich phase at higher Tss. In contrast, at higher Tcs, quenching from a higher Ts to Tc promotes nucleation as a result of more dramatic concentration fluctuation, leading to a faster overall crystallization rate. The overall crystallization rate of the PP/EPR in-reactor alloy prepared by multi-stage sequential polymerization process (MSSP) is retarded by increasing phase separation time (ts). However, prolonging phase separation time has little effect on the crystallization rate of the sample prepared by two-stage polymerization process (TSP). This result can be attributed to the different phase separation rates of these two samples. The SAXS result confirms that at higher Tc, phase separation in the melt before crystallization can retard crystallization, when compared with the directly quenched samples. It is also found that the phase-separated PP/EPR in-reactor alloys exhibit a larger long period because of more amorphous phases included between the lamellar crystals. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
Co-reporter:Bing Zhou, Zai-Zai Tong, Jie Huang, Jun-Ting Xu, Zhi-Qiang Fan
Materials Chemistry and Physics 2013 Volume 137(Issue 3) pp:1053-1061
Publication Date(Web):15 January 2013
DOI:10.1016/j.matchemphys.2012.11.027
Poly(ε-caprolactone) (PCL) was grafted onto multiwalled carbon nanotubes (MWNTs) with high grafting degrees. The surface of MWNTs was first modified by 2-hydroxyethyl benzocyclobutene (BCB-EO) via a [2 + 4] cyclo-addition reaction. Polymerization of ε-caprolactone was conducted in the presence of BCB-EO modified MWNTs and the catalyst stannous octoate. Alternatively, the grafted-BCB-EO first reacted with CpTiCl3 and then the reactant was used to catalyze polymerization of ε-caprolactone. The grafting degrees of PCL prepared from BCB-EO modified MWNTs can reach at least 94%, much higher than those prepared by other two conventional methods. TEM result shows that the morphology and thickness of the grafted PCLs strongly depend on the grafting degree and grafting method. The crystallization and melting behaviors of the MWNTs-grafted PCL were investigated. MWNTs can exert both nucleation and confinement effects on crystallization of the grafted PCL, leading to lower crystallinity but higher crystallization temperature (Tc) and melting temperature (Tm) of the grafted PCLs. It is found that crystallinity of the grafted PCLs increases with the grafting degree, but Tc and Tm also depend on the molecular weight.Highlights► MWNTs-grafted PCLs with high grafting degrees were prepared. ► The morphology and thickness of the grafted PCL depend on the grafting degree. ► MWNTs exert both confinement and nucleation effects on crystallization of PCL.
Co-reporter:Zai-Zai Tong;Sheng-Jie Xia ;Zhi-Qiang Fan
Polymer International 2013 Volume 62( Issue 2) pp:228-237
Publication Date(Web):
DOI:10.1002/pi.4288
Abstract
The microstructure and morphology of an olefinic blocky copolymer (OBC) and an ethylene-hexene copolymer prepared by conventional Ziegler-Natta catalysis (ZNEH) are compared. It is found that these two samples have similar melting temperatures, but the overall comonomer content in OBC is slightly higher. The crystallization temperature and crystallinity of OBC are markedly lower than those of ZNEH. A successive self-nucleation annealing experiment reveals that OBC has a more uniform distribution of crystal thickness, indicating a more homogeneous composition distribution in its hard blocks. Small-angle X-ray scattering (SAXS) results show that the long period of OBC hardly changes with temperature in the low-temperature range, whereas that of ZNEH increases gradually with temperature due to melting of the less perfect crystals. The average lamellar thickness of crystals is larger for OBC than for ZNEH, but the thickness of the thickest crystals is comparable in the two. The SAXS profiles were analyzed using a one-dimensional correlation function. The result reveals that the partially ordered interphases in OBC are mainly located at the interface of the crystalline and amorphous phases. In contrast, the interface of the crystalline and amorphous phases in ZNEH is quite sharp and it is inferred that the partially ordered interphases are distributed in the bulk as separated domains. Scattered tiny crystals are formed in ZNEH, but OBC exhibits a macroscopic morphology of large spherulites. It is also observed that more amorphous phases are rejected outside of the lamellar stacks and spherulites in OBC. © 2012 Society of Chemical Industry
Co-reporter:Jie Huang, Zai-Zai Tong, Bing Zhou, Jun-Ting Xu, Zhi-Qiang Fan
Polymer 2013 Volume 54(Issue 12) pp:3098-3106
Publication Date(Web):24 May 2013
DOI:10.1016/j.polymer.2013.03.070
In the present work, a poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) block copolymer was doped with LiClO4 at various salt concentrations. The morphology of the hybrids was characterized with time-resolved small-angle X-ray scattering (SAXS). It is observed that LiClO4 can induce microphase separation of the miscible PCL-b-PEO in the melt. With increase in doping ratio, the morphology of the hybrids changes from cylinder into lamella. The order–disorder transition temperature (TODT) and domain spacing increase with doping ratio in the low salt concentration range, but decrease at higher salt concentrations. FT-IR, UV and DSC results show that LiClO4 preferentially interacts with PEO at low doping ratios, but also associates with PCL at high doping ratios. The effective Flory–Huggins interaction parameters (χeff) for the hybrids were calculated. It is found that at low salt concentrations the χeff increases linearly with doping ratio due to selective interaction between PEO and LiCLO4, but the competitive interaction of LiClO4 with PCL and PEO at high salt concentration can lead to decrease of χeff.
Co-reporter:L. Liu;Z. Z. Tong;J. T. Xu;Z. Q. Fan
Journal of Thermal Analysis and Calorimetry 2013 Volume 114( Issue 2) pp:573-579
Publication Date(Web):2013 November
DOI:10.1007/s10973-013-3019-1
In the present work, successive self-nucleation and annealing (SSA) was applied to a series of tetrafluoroethylene-hexafluoropropylene random copolymers (FEPs). Multiple melting peaks were observed for all FEP samples after SSA thermal treatment. The lamellar crystal thicknesses were calculated from the melting temperatures, and the mass percentages of the crystals of specific thickness were obtained from the areas of the melting peaks. As a result, distributions of the lamellar thickness, which can be correlated to the composition distribution, were determined. It was found that the composition distribution of the FEP samples tended to become more heterogeneous as the content of hexafluoropropylene (HFP) comonomer increases. Samples with the same HFP content might also have different composition distributions.
Co-reporter:Wei-Na He, Jun-Ting Xu
Progress in Polymer Science 2012 Volume 37(Issue 10) pp:1350-1400
Publication Date(Web):October 2012
DOI:10.1016/j.progpolymsci.2012.05.002
The self-assembly of block copolymers (BCPs) in the presence of crystallization as the second driving force is reviewed, for BCPs in the bulk, thin films, single crystals and micelles. The crystallization of semicrystalline BCPs in the bulk is introduced briefly and the unique morphologies of semicrystalline BCPs at various levels due to crystallization are discussed. The thin film morphologies shown by crystalline BCPs are summarized in terms of the factors affecting the relative strengths of various driving forces. Special attention is paid to the thin film morphologies of functional BCPs containing crystalline poly(3-alkylthiophene) and perylene bisimide units. The single crystal morphologies of semicrystalline BCPs are also presented. Finally, the micellar morphologies of BCPs with a semicrystalline core are reviewed. The controlled and living growth of crystalline micelles, which is the unique characteristic of such micelle, is then discussed.
Co-reporter:Yi-Min Liu;Ying Li;Zhi-Sheng Fu ;Zhi-Qiang Fan
Journal of Applied Polymer Science 2012 Volume 123( Issue 1) pp:535-542
Publication Date(Web):
DOI:10.1002/app.34478
Abstract
In this work, the effect of phase separation on the spherulitic growth rate of a polypropylene/ethylene–propylene random (PP/EPR) copolymer in-reactor alloy was investigated. The PP/EPR in-reactor alloy was either directly quenched from homogeneous melt to crystallization temperature or held at various temperatures for phase separation prior to crystallization. It is found that at lower crystallization temperatures previous phase separation in the melt retards the crystallization rate. The higher the phase separation rate, the smaller the spherulitic growth rate. This can be attributed to faster crystallization rate than the rate of secondary phase separation. The composition of the PP-rich phase and corresponding depression of the equilibrium melting temperature of PP vary with phase separation temperature. On the other hand, at higher crystallization temperature, previous phase separation in the melt has little effect on the spherulitic growth rate because secondary phase separation can take place prior to crystallization. The transition temperature from regime II to regime III also shifts to lower temperature as the phase separation temperature increases. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Co-reporter:Bing Zhou;Yi-Liao Liu;Zhi-Qiang Fan
Journal of Applied Polymer Science 2012 Volume 123( Issue 6) pp:3321-3330
Publication Date(Web):
DOI:10.1002/app.34973
Abstract
Films of polypropylene/organically modified montmorillonite (PP/OMMT) nanocomposites were drawn at two different temperatures with various draw ratios. The effect of OMMT on the orientations of the crystalline and amorphous phases was studied using polarized infrared spectroscopy. It is found that OMMT layers always retard the orientation of the crystalline phase. The higher the OMMT loading, the stronger the retardance effect. In contrast, the effect of OMMT layers on the orientation of the amorphous phase depends on draw temperature and OMMT loading. A favorable effect on the orientation of the amorphous phase is observed at low OMMT loading and high draw temperature, but the retardance prevails at high OMMT loading and low draw temperature. The favorable effect on orientation at high draw temperature is attributed to the stabilization effect of OMMT layers on the conformation of amorphous PP chains. Such an effect was further verified by comparing the crystallization behavior and the morphologies of drawn PP and PP/OMMT films crystallized from 180°C. Memory effect is observed for crystallization of drawn PP/OMMT film, but it is not obvious for the drawn film of neat PP. Spherulites are formed for orientated neat PP films cooled from 180°C, but cylindrites are still formed after the drawn PP/OMMT films undergo melting at 180°C and recrystallization. The stabilization effect disappears at higher temperature (230°C). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
Co-reporter:Wei-Na He;Bin-Yang Du;Zhi-Qiang Fan;Fang-Li Sun
Macromolecular Chemistry and Physics 2012 Volume 213( Issue 9) pp:952-964
Publication Date(Web):
DOI:10.1002/macp.201100615
Abstract
The effect of pH on the micellar morphology of a semicrystalline poly(ϵ-caprolactone)-block-poly(ethylene oxide) block copolymer (PCL66-b-PEO44) in aqueous solution is investigated. Spherical micelles are formed in neutral and acidic solutions. However, addition of alkali to the neutral micellar solution triggers a sphere-to-cylinder transformation of the micellar morphology. The micelles are stable in both neutral and acidic solutions, but the size of the micelles becomes gradually larger in the alkali solution. This phenomenon is interpreted in terms of the effect of pH value on the reduced tethering density of the corona in the semicrystalline micelles.
Co-reporter:Kai Cao 徐君庭;Xiao-song Wang 王晓松
Chinese Journal of Polymer Science 2012 Volume 30( Issue 5) pp:674-681
Publication Date(Web):2012 September
DOI:10.1007/s10118-012-1161-z
In this work, a new type of block polymers, polystyrene-b-poly[(N-isopropyl acrylamide)-co-(vinyl benzyl chloride)] (PS-b-P(NIPAM-co-VBC)), was prepared via reversible addition fragmentation transfer polymerization, then pentacyano(4-(dimethylamino pyridine))ferrate (Fe-DMAP) was attached to VBC units through a quaternization process. The Fe(II)-coordinated PS-b-P[NIPAM-co-(VBC-Fe-DMAP)] block copolymers were characterized by 1H-NMR, FT-IR and TGA. The self-assembly behavior of the block copolymers was also investigated and the micelle morphology was characterized by TEM. It was found that the PS-b-P(NIPAM-co-VBC) block polymer and Fe-coordinated block copolymer could both form spherical micelles in DMF/MeOH mixed solvent.
Co-reporter:Lian Wang, Xinfei Yu, Shuguang Yang, Joseph X. Zheng, Ryan M. Van Horn, Wen-Bin Zhang, Junting Xu, and Stephen Z. D. Cheng
Macromolecules 2012 Volume 45(Issue 8) pp:3634-3638
Publication Date(Web):April 9, 2012
DOI:10.1021/ma3002752
Co-reporter:Wei-Na He, Bing Zhou, Jun-Ting Xu, Bin-Yang Du, and Zhi-Qiang Fan
Macromolecules 2012 Volume 45(Issue 24) pp:9768-9778
Publication Date(Web):December 4, 2012
DOI:10.1021/ma301267k
The micelles of a poly(ε-caprolactone)-b-poly(ethylene oxide) block copolymer (PCL59-b-PEO113) in different mixed solvents were held at 53 °C for 5 min, and seed solutions with different micellar morphologies and amounts of micellar semicrystalline seeds were prepared. The crystallinity of these seed micelles was identified by high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). It is found that mostly amorphous spherical micelles are formed by heating micellar solutions in H2O/THF (5/1 v/v) and H2O/dioxane (5/1 v/v) mixed solvents, a mixture of amorphous spherical micelles and short semicrystalline cylindrical micelles is yielded in H2O/DMF (5/1 v/v), whereas mostly short semicrystalline cylindrical micelles are obtained in H2O/DMSO (5/1 v/v) mixed solvent. The seed solutions were placed at 4 °C for micellar growth. Transmission electron microscope (TEM) shows that micellar growth driven by epitaxial crystallization of core-forming PCL chains takes place and the length of grown cylindrical micelles increases with time. Two growth modes are observed. One is the growth of unimers (or amorphous spherical micelles) on the active ends of semicrystalline cylindrical micelles in micellar solution in H2O/DMF (5/1 v/v) at the initial growth period. The other is the growth by end-to-end coupling of cylindrical micelles in H2O/DMSO (5/1 v/v). The kinetics of micellar growth is strongly dependent on the growth mechanism. The growth of the cylindrical micelles in the H2O/DMF (5/1 v/v) solution is much faster than that in the H2O/DMSO (5/1 v/v) solution. On long time scale, micellar growth by end-to-end coupling of semicrystalline cylindrical micelles occurs with slow rate in both H2O/DMF (5/1 v/v) and H2O/DMSO (5/1 v/v) solutions, and the growth rate in H2O/DMF (5/1 v/v) solution is even slower than that in H2O/DMSO (5/1 v/v).
Co-reporter:Yi-Liao Liu, Ying Li, Jun-Ting Xu and Zhi-Qiang Fan
ACS Applied Materials & Interfaces 2010 Volume 2(Issue 6) pp:1759
Publication Date(Web):May 18, 2010
DOI:10.1021/am1002525
Poly(vinylidene difluoride)/organically modified montmorillonite (PVDF/OMMT) composite nanofibers were prepared by electrospinning the solution of PVDF/OMMT precursor in DMF. Wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) show that in the bulk of the PVDF/OMMT precursor OMMT platelets are homogeneously dispersed in PVDF and can be both intercalated and exfoliated. It is found that the diameter of the PVDF/OMMT composite nanofibers is smaller than that of the neat PVDF fibers because the lower viscosity of PVDF/OMMT solution, which is attributed to the possible adsorption of PVDF chains on OMMT layers and thus reduction in number of entanglement. The crystal structure of the composite nanofibers was investigated using WAXD and Fourier transform infrared (FT-IR) and compared with that of thin film samples. The results show that the nonpolar α phase is completely absent in the electrospun PVDF/OMMT composite nanofibers, whereas it is still present in the neat PVDF electrospun fibers and in the thin films of PVDF/OMMT nanocomposites. The cooperative effect between electrospinning and nanoclay on formation of polar β and γ crystalline phases in PVDF is discussed. The IR result reveals that electrospinning induces formation of long trans conformation, whereas OMMT platelets can retard relaxation of PVDF chains and stabilize such conformation due to the possible interaction between the PVDF chains and OMMT layers. This cooperative effect leads to extinction of nonpolar α phase and enhances the polar β and γ phases in the electrospun PVDF/OMMT composite nanofibers.Keywords: clay; crystallization; electrospinning; poly(vinylidene fluoride)
Co-reporter:Wei-Na He;Bin-Yang Du;Zhi-Qiang Fan;Xiaosong Wang
Macromolecular Chemistry and Physics 2010 Volume 211( Issue 17) pp:1909-1916
Publication Date(Web):
DOI:10.1002/macp.201000184
Co-reporter:Min Cao;Jian-Qi Wang;Peng-Cheng Chen;Zhi-Qiang Fan
Journal of Polymer Science Part A: Polymer Chemistry 2010 Volume 48( Issue 17) pp:3834-3840
Publication Date(Web):
DOI:10.1002/pola.24169
Abstract
In this work, the polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymers with a trithiocarbonate group between the blocks were prepared by polymerization of styrene in the presence of a trithiocarbonate reversible addition fragmentation chain transfer (RAFT) agent connected with PEO. Decomposition of the trithiocarbonate group by UV irradiation was investigated in three different types of solvent: tetrahydrofuran (THF, common solvent for both blocks), cyclohexane/dioxane mixture (selective solvent for the PS block) and N,N-dimethylformamide (DMF)/ethanol mixture (selective solvent for the PEO block). It is found that cleavage of the block copolymers can take place in all these three solvents and the cleavage ratio ranges from 76 to 86%. The micellar morphologies in selective solvents before and after cleavage were examined. It is observed that the size of the micelles is reduced after cleavage and sometimes aggregation of the micelles occurs due to removal of the corona of micelles. It shows that this work provides a facile and general method for synthesis of cleavable block copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3834–3840, 2010
Co-reporter:Zi-Xiu Du, Jun-Ting Xu, Qi Dong, Zhi-Qiang Fan
Polymer 2009 50(11) pp: 2510-2515
Publication Date(Web):
DOI:10.1016/j.polymer.2009.04.006
Co-reporter:Ying Li, Jun-Ting Xu, Qi Dong, Zhi-Sheng Fu, Zhi-Qiang Fan
Polymer 2009 50(21) pp: 5134-5141
Publication Date(Web):
DOI:10.1016/j.polymer.2009.09.008
Co-reporter:Zi-Xiu Du;Zhi-Qiang Fan
Macromolecular Rapid Communications 2008 Volume 29( Issue 6) pp:467-471
Publication Date(Web):
DOI:10.1002/marc.200700795
Co-reporter:Yuan-Jin Qiu;Liang Xue;Zhi-Qiang Fan;Zhong-Hua Wu
Journal of Applied Polymer Science 2007 Volume 103(Issue 4) pp:2464-2471
Publication Date(Web):22 NOV 2006
DOI:10.1002/app.25362
Crystallization and morphology of polyethylene glycol with molecular weight Mn = 2000 (PEG2000) capped with cholesterol at one end (CS-PEG2000) and at both ends (CS-PEG2000-CS) were investigated. It is found that the bulky cholesteryl end group can retard crystallization rate and decrease crystallinity of PEG, especially for CS-PEG2000-CS. Isothermal crystallization kinetics shows that the Avrami exponent of CS-PEG2000 decreases as crystallization temperature (Tc). The Avrami exponent of CS-PEG2000-CS increases slightly with Tc, but it is lower than that of CS-PEG2000. Compared to the perfect spherulite morphology of PEG2000, CS-PEG2000 exhibits irregular and leaf-like spherulite morphology, while only needle-like crystals are observed in CS-PEG2000-CS. The linear growth rate of CS-PEG2000 shows a stronger dependence on Tc than PEG2000. The cholesterol end group alters not only the free energy of the folding surface, but also the temperature range of crystallization regime. The small angle X-ray scattering (SAXS) results show that lamellar structures are formed in all these three samples. By comparing the long periods obtained from SAXS with the theoretically calculated values, we find that the PEG chains are extended in PEG2000 and CS-PEG2000, but they are once-folded in CS-PEG2000-CS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2464–2471, 2007
Co-reporter:Zi-Xiu Du;Yong Yang;Zhi-Qiang Fan
Journal of Applied Polymer Science 2007 Volume 104(Issue 5) pp:2986-2991
Publication Date(Web):28 FEB 2007
DOI:10.1002/app.25932
The spherulitic growth rates of a series poly (ϵ-caprolactone) homopolymers and poly(ϵ-caprolactone)-b- poly(ethylene glycol) (PCL-b-PEG) block copolymers with different molecular weights but narrow polydispersity were studied. The results show that for both PCL homopolymers and PCL-b-PEG block copolymers, the spherulitic growth rate first increases with molecular weight and reaches a maximum, then decreases as molecular weight increases. Crystallization temperature has greater influence on the spherulitic growth rate of polymers with higher molecular weight. Hoffman–Lauritzen theory was used to analyze spherulitic growth kinetics and the free energy of the folding surface (σe) was derived. It is found that the values of σe decrease with molecular weight at low molecular weight level and become constant for high molecular weight polymers. The chemically linked PEG block does not change the values of σe significantly. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Co-reporter:Zi-Xiu Du;Yong Yang;Zhi-Qiang Fan
Journal of Applied Polymer Science 2007 Volume 105(Issue 2) pp:771-776
Publication Date(Web):2 APR 2007
DOI:10.1002/app.26113
A series of poly(ϵ-caprolactone)-b-poly(ethylene glycol) (PCL-b-PEG) block copolymers with different molecular weights were synthesized with a salicylaldimine-aluminum complex in the presence of monomethoxy poly(ethylene glycol). The block copolymers were characterized by 1H NMR, GPC, WAXD, and DSC. The 1H NMR and GPC results verify the block structure and narrow molecular weight distribution of the block copolymers. WAXD and DSC results show that crystallization behavior of the block copolymers varies with the composition. When the PCL block is extremely short, only the PEG block is crystallizable. With further increase in the length of the PCL block, both blocks can crystallize. The PCL crystallizes prior to the PEG block and has a stronger suppression effect on crystallization of the PEG block, while the PEG block only exerts a relatively weak adverse effect on crystallization of the PCL block. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Co-reporter:Guo-Dong Liang;Zhi-Qiang Fan;Guo-Dong Liang;Zhi-Qiang Fan
Journal of Applied Polymer Science 2006 Volume 102(Issue 3) pp:2632-2638
Publication Date(Web):23 AUG 2006
DOI:10.1002/app.24037
A series of polystyrene-b-polybutadiene (PSt-b-PBd) block copolymers with various chain lengths and compositions were synthesized by sequential living anionic polymerization and then converted into the corresponding polystyrene-b-poly(ethylene-co-butene) (PSt-b-PEB) block copolymers through the selective hydrogenation of unsaturated polybutadiene segments. Noncatalytic hydrogenation was carried out with diimide as the hydrogen source. The microstructures of PSt-b-PBd and PSt-b-PEB were investigated with gel permeation chromatography, 1H-NMR, 13C-NMR, Fourier transform infrared, and differential scanning calorimetry. The results showed that the hydrogenation reaction was conducted successfully and that the chain length and molecular weight distribution were not altered by hydrogenation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2632–2638, 2006
Co-reporter:Jun-Ting Xu;Yan-Qin Zhao;Qi Wang;Zhi-Qiang Fan
Macromolecular Rapid Communications 2005 Volume 26(Issue 8) pp:620-625
Publication Date(Web):21 APR 2005
DOI:10.1002/marc.200400595
Summary: Exfoliated and intercalated polyethylene/montmorillonite (PE/MMT) nanocomposites with high MMT content were prepared by in situ polymerization. The isothermal crystallization kinetics of the nanocomposites were analyzed with Lauritzen–Hoffman regime theory. Regime III crystallization, which is difficult to observe in linear polyethylene, appears in the PE/MMT nanocomposites. The broader temperature range of regime III crystallization in PE/MMT nanocomposites shows that the mobility and reptation ability of the PE chains are greatly reduced by the MMT, especially in the intercalated nanocomposite.
Co-reporter:Jun-Ting Xu;Yu-Jin Zhang;Fang-Xiao Guan;Zhi-Qiang Fan
Journal of Applied Polymer Science 2005 Volume 97(Issue 1) pp:240-247
Publication Date(Web):22 APR 2005
DOI:10.1002/app.21213
Isothermal crystallization and subsequent melting behavior of two propylene/hexene-1 copolymers and two propylene/octene-1 copolymers prepared with metallocene catalyst were investigated. It is found that γ-modification is predominant in all copolymers. The Avrami exponent shows a weak dependency on comonomer content and comonomer type. At higher crystallization temperatures (Tc) the crystallization rate constant changes more rapidly with Tc and the crystallization half-time substantially increases. Double melting peaks were also observed at high Tc, which is attributed to the inhomogeneous distribution of comonomer units along the polymer chains and the existence of crystals with different lamellar thicknesses. The equilibrium melting temperatures (T) of the copolymers were obtained by Hoffman–Weeks extrapolation. It was found that the T decreases with increasing comonomer content, but are independent of comonomer type, implying that comonomer units are excluded from the crystal lattice. Dilation of the crystal lattice was also observed, which depends on crystallization, comonomer content, and comonomer type. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 240–247, 2005
Co-reporter:Wei Jin;Zhi-Qiang Fan
Journal of Applied Polymer Science 2005 Volume 98(Issue 1) pp:208-215
Publication Date(Web):12 JUL 2005
DOI:10.1002/app.22060
Low-molecular-weight hydrogenated polybutadiene-b-poly(ethylene glycol) (HPBd-b-PEG) block copolymers with double crystallizable blocks were synthesized by the coupling of hydroxyl-end-group-containing hydrogenated polybutadiene and poly(ethylene glycol) with terephthaloyl chloride as a coupling reagent. The block structure was confirmed by 1H-NMR, and the molecular weights of the blocks were determined as well. Gel permeation chromatography showed that the HPBd-b-PEG block copolymers had narrow molecular weight distributions. The crystallization and superstructures of the HPBd-b-PEG block copolymers were studied with differential scanning calorimetry, wide-angle X-ray diffraction (WAXD), and polarized optical microscopy. The results revealed that the crystallization of both blocks was suppressed mutually, especially for the shorter block. WAXD patterns showed that the crystal structures remained unchanged for both blocks. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 208–215, 2005
Co-reporter:Jun-Ting Xu;Zhi-Sheng Fu;Zhi-Qiang Fan;Wei Jin
Journal of Applied Polymer Science 2005 Volume 98(Issue 1) pp:243-246
Publication Date(Web):12 JUL 2005
DOI:10.1002/app.22085
Fragmentation was observed in the polymerization process for the preparation of a polypropylene (PP)/poly(ethylene-co-propylene) (EPR) in situ alloy. Composition distributions of different polymer particles were analyzed by preparative temperature-rising elution fractionation. The fractions eluted at room temperature and 96, 110, and 117°C were selected for 13C-NMR characterization. There was more propylene homopolymer and ethylene–propylene block copolymer in the large particles, whereas the small particles contained more ethylene–propylene random copolymer and copolymer with a transition microstructure. On the basis of the formation mechanism of various components in the PP/EPR alloy, we inferred that the fragmentation of the polymer particles mainly took place in the copolymerization step. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 243–246, 2005
Co-reporter:Jun-Ting Xu;Zhi-Sheng Fu;Xian-Ping Wang;Jun-Sheng Geng;Zhi-Qiang Fan
Journal of Applied Polymer Science 2005 Volume 98(Issue 2) pp:632-638
Publication Date(Web):26 JUL 2005
DOI:10.1002/app.22074
Four polyolefin in-reactor alloys with different compositions and structures were prepared by sequential polymerization. All the alloys were fractionated into five fractions: a random copolymer of ethylene and propylene (25°C fraction), an ethylene–propylene segmented copolymer (90°C fraction), an ethylene homopolymer (110°C fraction), an ethylene–propylene block copolymer (120°C fraction), and a propylene homopolymer plus a minor ethylene homopolymer of high molecular weight (>120°C fraction). The effect of the structure on the morphology and spherulitic growth kinetics of the polypropylene (PP) component in the alloys was investigated. The polyolefin alloys containing a suitable block copolymer fraction and a larger amount of PP had a more homogeneous morphology, and the crystalline particles were smaller. Quenching the polyolefin alloys led to smaller crystallites and a more homogeneous morphology as well. Isothermal crystallization was carried out above the melting temperature of polyethylene, and the growth of PP spherulites was monitored with polarized optical microscopy with a hot stage. The alloys with higher propylene contents exhibited a faster spherulitic growth rate. The fold surface free energy was derived, and it was found that a large amount of block copolymer fractions and random copolymer fractions could reduce the fold surface free energy. The structure of the alloys also affected the crystallization regime of PP. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 632–638, 2005
Co-reporter:Jun-Ting Xu;Liang Xue;Shao-Min Mai;A. J. Ryan
Journal of Applied Polymer Science 2004 Volume 93(Issue 2) pp:870-876
Publication Date(Web):23 APR 2004
DOI:10.1002/app.20490
The nonisothermal crystallization and morphology of three oxyethylene–oxybutylene block copolymers with different architectures (E50B70, B65E75B65, and E35B114E35) were compared with those of three blends (E56B27/B14, B37E77B37/B14, and E38B38E38/B14) with the same composition and morphology (E and B represent oxyethylene and oxybutylene units, respectively, and the subscripts denote the degree of polymerization), and the effect of the amorphous block was examined. The neat block copolymers had larger d-spacings and higher melting temperatures than the corresponding blends. In nonisothermal crystallization, the neat block copolymers had lower crystallization temperatures at high cooling rates. The difference in the crystallization temperatures became smaller at low cooling rates, and some of the neat block copolymers could have higher crystallization temperatures. Polarized optical microscopy showed that the neat block copolymers had smaller dimensions of crystal growth and smaller size of spherulites than the blends. The lower crystallization temperatures and less perfect morphology were attributed to the slower rate of conformational rearrangement of the amorphous block, which was required by the chain folding of the crystallizable block. This effect was more evident in the E35B114E35 triblock copolymer, in which both ends of the amorphous B block were immobilized at the interface. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 870–876, 2004
Co-reporter:Jun-Ting Xu;Zhi-Qiang Fan;Liang Xue;Liang Xue;Zhi-Qiang Fan
Journal of Applied Polymer Science 2004 Volume 93(Issue 4) pp:1724-1730
Publication Date(Web):2 JUN 2004
DOI:10.1002/app.20643
The nonisothermal crystallization behavior of one metallocene-based isotactic polypropylene and three propylene–decene-1 copolymers was studied. The effects of comonomer content and cooling rate were investigated. It was found that comonomer units enchained systematically reduce the crystallization temperature (Tc), melting temperature (Tm), fusion enthalpy (ΔHf), and crystallinity (Xc). Such an effect becomes more evident at a faster cooling rate. With increasing comonomer content, the supercooling required for crystallization increases and the overall crystallization rate is reduced. The Avrami equation is applicable to describe the nonisothermal crystallization kinetics of propylene–decene-1 copolymer. It was shown that, although the reduced crystallization rate constant Zc increases with comonomer content, the Avrami exponent decreases with comonomer content and cooling rate, leading to the smaller overall crystallization rate and larger crystallization half-time of the copolymer with higher comonomer content. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1724–1730, 2004
Co-reporter:Jun-Ting Xu, Jian-Jun Yuan, Si-Yuan Cheng
European Polymer Journal 2003 Volume 39(Issue 11) pp:2091-2098
Publication Date(Web):November 2003
DOI:10.1016/S0014-3057(03)00155-1
Crystallization of a polystyrene-b-poly(ethylene oxide)-b-polystyrene (S–EO–S) triblock copolymer, S40EO136S40, with lamellar morphology in the melt and low glass transition temperature (Tg=47 °C) of the S block was studied. The triblock copolymer was cooled from ordered melt and isothermal crystallization was conducted at crystallization temperatures (Tc) near the Tg of the S block. It is found that crystallization behavior of S40EO136S40 strongly depends on Tc. When Tc is far below Tg, an Avrami exponent n=0.5 is observed, which is attributed to diffusion-controlled confined crystallization. As Tc slightly increases, the Avrami exponent is 1.0, indicating that crystallization is confined and crystallization rate is determined by the rate of homogeneous nucleation. When Tc is just below the Tg of the S block, crystallization tends to become breakout and accordingly Avrami exponent changes from 1.0 to 3.2. Crystallinity and melting temperature of the EO block in breakout crystallization are slightly higher than those in confined crystallization. Time-resolved small and wide angle X-ray scattering (SAXS/WAXS) were used to monitor isothermal crystallization of S40EO136S40. It shows that the long period is constant in confined crystallization, but it gradually increases during breakout crystallization. WAXS result reveals that confined or breakout crystallization has no effect on the crystal structure of the EO block.
Co-reporter:Wei-Na He, Jun-Ting Xu
Progress in Polymer Science (October 2012) Volume 37(Issue 10) pp:1350-1400
Publication Date(Web):1 October 2012
DOI:10.1016/j.progpolymsci.2012.05.002
The self-assembly of block copolymers (BCPs) in the presence of crystallization as the second driving force is reviewed, for BCPs in the bulk, thin films, single crystals and micelles. The crystallization of semicrystalline BCPs in the bulk is introduced briefly and the unique morphologies of semicrystalline BCPs at various levels due to crystallization are discussed. The thin film morphologies shown by crystalline BCPs are summarized in terms of the factors affecting the relative strengths of various driving forces. Special attention is paid to the thin film morphologies of functional BCPs containing crystalline poly(3-alkylthiophene) and perylene bisimide units. The single crystal morphologies of semicrystalline BCPs are also presented. Finally, the micellar morphologies of BCPs with a semicrystalline core are reviewed. The controlled and living growth of crystalline micelles, which is the unique characteristic of such micelle, is then discussed.
Co-reporter:Jun-Huan Li, Yuyin Xi, Lilo D. Pozzo, Jun-Ting Xu and Christine K. Luscombe
Journal of Materials Chemistry A 2017 - vol. 5(Issue 21) pp:NaN5134-5134
Publication Date(Web):2017/05/12
DOI:10.1039/C7TC01419H
The nanoscale structure and macroscopic morphology of π-conjugated polymers are very important for their electronic application. While ordered single crystals of small molecules have been obtained via solution deposition, macroscopically aligned films of π-conjugated polymers deposited directly from solution have always required surface modification or complex pre-deposition processing of the solution. Here, ordered nanowires were obtained via shear-enhanced crystallization of π-conjugated polymers at the air–liquid–solid interface using simple deposition of the polymer solution onto an inclined substrate. The formation of macroscopically aligned nanowire arrays was found to be due to the synergy between intrinsic (π-conjugated backbone) and external (crystallization conditions) effects. The oriented nanowires showed remarkable improvement in the charge carrier mobility compared to spin-coated films as characterized in organic field-effect transistors (OFETs). Considering the simplicity and large-scale applicability, shear-enhanced crystallization of π-conjugated polymers provides a promising strategy to achieve high-performance polymer semiconductor films for electronics applications.
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