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991.
Lucineide Balbino da Silva Marcelo Massayoshi Ueki Marcelo Farah Vitor Manuel Coelho Barroso João Manuel Luis Lopes Maia Rosario Elida Suman Bretas 《Rheologica Acta》2006,45(3):268-280
Blends of polyethylene terephthalate (PET) with a liquid crystalline polymer (LCP) and a compatibilizer were produced by twin
screw extrusion and injection molding. Transesterification and compatibilization studies were made in a torque rheometer.
The morphology of the injection-molded plaques was studied by scanning electron microscopy. The blends shear growth function
was measured in a cone and plate rheometer. The elongational growth function
was measured in a modified rotational rheometer. Transesterification was observed in the PET/LCP/compatibilizer 95/5/0 blend.
The injection-molded plaques displayed the usual “skin-core” morphology. All the blends were highly shear-thinning, even at
low shear rates; thus, a zero-shear viscosity could not be calculated. The compatibilized blend had the highest shear viscosity
of all the blends, confirming the strong PET/LCP interphase and the effectiveness of the compatibilizing agent. On the other
hand, the 90/10/0 blend had the lowest shear viscosity. All the blends showed strain softening behavior, similar to the PET.
The 90/10/0 blend had the highest elongational growth function, while the 95/5/0 had the lowest. The compatibilized blend
had an intermediate behavior between both blends. 相似文献
992.
The bonding and crystalline structures of oil‐fried fly ash collected from a power plant were analyzed by using Raman spectroscopy and X‐ray diffraction (XRD), respectively. These carbon powders underwent a series of annealing treatment for graphitization and crystallization. In Raman spectra, the refined, unburned carbon contains clearly the D, G and D′ peaks under 2000 or 2700 °C treatment. The Raman spectral line shape of refined, unburned carbon heated at 2700 °C is similar to that of commercial graphite made from graphitization process. In the XRD spectra, the refined, unburned carbon contains (002), (100) and (004) diffraction peaks under heating at 2000 or 2700 °C. The XRD spectral line shape of refined, unburned carbon heated at 2700 °C is similar to that of a commercial graphite bar. The quantitative graphitization level from Raman spectra and crystallization degree from XRD spectra on refined, unburned carbon powders serve as preliminary guide for the qualitative evaluation of these unburned carbon powders. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
993.
994.
Arun K. Kalkar Vineeta D. Deshpande Milind J. Kulkarni 《Journal of Polymer Science.Polymer Physics》2010,48(10):1070-1100
The article deals with the melting and nonisothermal crystallization behavior of neat poly (phenylene sulphide) (PPS) and its composites with a thermotropic liquid crystalline polymer (TLCP)—Vectra A950, prepared by melt mixing and probed by differential scanning calorimetry. The various macrokinetic models namely, the Ozawa, the modified Avrami, the Tobin, and the Mo models were applied to describe the crystallization kinetics under nonisothermal conditions. The kinetic crystallizabilty of PPS/TLCP composites calculated using the approach of Ziabicki varies depending on these two composite composition‐induced effects. Similarly Mo model predicts that to obtain a higher degree of crystallizabilty for PPS/TLCP composites, a higher cooling rate should be used. The effective energy barrier based on the differential isoconversional method of Friedman is found to be an increasing function of relative degree of melt conversion. The effect is explained in terms of nucleation theory proposed by Wunderlich to crystallization of polymers. The Lauritzen–Hoffman parameters are estimated using G = 1/t0.5 effective activation energy equation proposed by Vyazovkin and Sbirrazzuoli. The Kg values estimated from latter equations are more comparable with values obtained using isothermal crystallization data than 1/t0.5 method. Furthermore, the kinetic analysis using this equation shows a regime transition from regime II to regime III for 100/00, 90/10, 80/20 PPS/TLCP composites, basically attributed to reduced mobility of PPS chains in composites. This regime II to III transition is accompanied by a morphological transition from defective spherulitic sheaf‐like structures to ordered sheaf‐like structures. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1070–1100, 2010 相似文献
995.
Chang‐An Yang Guo Wang Helou Xie Qing Wang Hailiang Zhang Erqiang Chen Qifeng Zhou 《Journal of polymer science. Part A, Polymer chemistry》2010,48(5):1149-1159
The first‐ and second‐generation dendronized polymers containing azobenzene mesogen were designed and successfully synthesized via free radical polymerization. The chemical structures of the monomers were confirmed by elemental analysis, 1H NMR, and 13C NMR. The molecular characterizations of the polymers were performed with 1H NMR and gel permeation chromatography. The phase structures and transition behaviors were studied using differential scanning calorimetry, polarized light microscopy, and small‐angle X‐ray scatter experiments. The experiment results revealed that the first‐generation dendronized polymer exhibited liquid crystalline behavior of the conventional side‐chain liquid crystalline polymer with azobenzene mesogen, that is, the polymer exhibited smectic phase structure at lower temperature and nematic phase structure at higher temperature. However, the second‐generation dendronized polymers exhibited more versatile intriguing liquid crystalline structures, namely smectic phase structure at lower temperature and columnar nematic phase structure at higher temperature, and moreover, the phase structure still remained before the decomposition temperature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1149–1159, 2010 相似文献
996.
Shaoyong Huang Shichun Jiang Lijia An Xuesi Chen 《Journal of Polymer Science.Polymer Physics》2008,46(13):1400-1411
The crystallization behaviors and morphology of asymmetric crystalline–crystalline diblock copolymers poly(ethylene oxide‐lactide) (PEO‐b‐PLLA) were investigated using differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXD), and microscopic techniques (polarized optical microscopy (POM) and atomic force microscopy (AFM)). Both blocks of PEO5‐b‐PLLA16 can be crystallized, which was confirmed by WAXD, while PEO block in PEO5‐b‐PLLA30 is difficult to crystallize because of the confinement induced by the high glass transition temperature and crystallization of PLLA block with the microphase separation of the block copolymer. Comparing with the crystallization and morphology of PLLA homopolymer and differences between the two copolymers, we studied the influence of PEO block and microphase separation on the crystallization and morphology of PLLA block. The boundary temperature (Tb) was observed, which distinguishes the crystallization into high‐ and low‐temperature ranges, the growth rate and morphology were quite different between the ranges. Crystalline morphologies including banded spherulite, dendritic crystal, and dense branching in PEO5‐b‐PLLA16 copolymer were formed. The typical morphology of dendritic crystals including two different sectors were observed in PEO5‐b‐PLLA30 copolymer, which can be explained by secondary nucleation, chain growth direction, and phase separation between the two blocks during the crystallization process. Lozenge‐shaped crystals of PLLA with screw dislocation were also observed employing AFM, but the crystalline morphology of PEO block was not observed using microscopy techniques because of its small size. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1400–1411, 2008 相似文献
997.
Jesús del Barrio Luis Oriol Rafael Alcalá Carlos Sánchez 《Journal of polymer science. Part A, Polymer chemistry》2010,48(7):1538-1550
A range of block copolymers (BCs) consisting of a linear poly(methyl methacrylate) (PMMA) block linked to an aliphatic polyester dendron functionalized with azobenzene moieties have been synthesized by sequential atom transfer radical polymerization (ATRP) and Click Chemistry. Two alkyne‐functionalized PMMA homopolymers with different molecular weights were obtained by ATRP and coupled to generations 2 to 4 of azodendrons bearing an azide group at the focal points. In the case of the azodendron with the highest generation number, the length of the flexible spacer attaching the cyanoazobenzene units to the dendron has also been modified. The coupling of both blocks and purity of BCs were checked by gel permeation chromatography, nuclear magnetic resonance, and infrared spectroscopy. The thermal transitions and liquid crystalline behavior of the BCs were investigated by differential scanning calorimetry and polarized‐light optical microscopy. A morphological study was carried out by transmission electron microscopy, using samples annealed at 115 °C. Photo‐induced anisotropy was induced in thin films of these materials after annealed at 115 °C. The highest stable birefringence values were obtained for the BCs bearing 8 and 16 azobenzene units in the dendritic block. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1538–1550, 2010 相似文献
998.
N. Gidopoulos S. Sorella E. Tosatti 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):217-226
We study the quantum phase transition between a band (“ionic”) insulator and a Mott-Hubbard insulator, realized at a critical
value in a bipartite Hubbard model with two inequivalent sites, whose on-site energies differ by an offset . The study is carried out both in D=1 and D=2 (square and honeycomb lattices), using exact Lanczos diagonalization, finite-size scaling, and Berry's phase calculations
of the polarization. The Born effective charge jump from positive infinity to negative infinity previously discovered in D=1 by Resta and Sorella is confirmed to be directly connected with the transition from the band insulator to the Mott insulating
state, in agreement with recent work of Ortiz et al. In addition, symmetry is analysed, and the transition is found to be associated with a reversal of inversion symmetry in
the ground state, of magnetic origin. We also study the D=1 excitation spectrum by Lanczos diagonalization and finite-size scaling. Not only the spin gap closes at the transition,
consistent with the magnetic nature of the Mott state, but also the charge gap closes, so that the intermediate state between
the two insulators appears to be metallic. This finding, rationalized within Hartree-Fock as due to a sign change of the effective
on-site energy offset for the minority spin electrons, underlines the profound difference between the two insulators. The band-to-Mott insulator
transition is also studied and found in the same model in D=2. There too we find an associated, although weaker, polarization anomaly, with some differences between square and honeycomb
lattices. The honeycomb lattice, which does not possess an inversion symmetry, is used to demonstrate the possibility of an
inverted piezoelectric effect in this kind of ionic Mott insulator.
Received 21 May 1999 相似文献
999.
R. Watanabe T. Iyoda T. Yamada H. Yoshida 《Journal of Thermal Analysis and Calorimetry》2006,85(3):713-717
Phase transition process of PEOm-b-PMA(Az)n was investigated
by the simultaneous DSC-XRD measurement using the synchrotron radiation facility.
Four endothermic DSC peaks were observed during heating process. These DSC
peaks were assigned to the melting of PEO, the transition from SmX, which
is a mixture of super-cooled SmC and crystal, to SmC, from SmC to SmA, and
from SmA to isotropic liquid state as determined by XRD profiles. In SmC phase,
the liner expansion coefficient calculated from the spacing variation of the
smectic layer distance was larger than that of the other phases. This result
reflected the fact azobenzene moieties in the long-side chains of PMA(Az)n
forming the smectic layers and then they were tilted and stood up during the
heating process. 相似文献
1000.
Yong‐feng Zhao Yi Yi Xinghe Fan Xiaofang Chen Xinhua Wan Qi‐Feng Zhou 《Journal of polymer science. Part A, Polymer chemistry》2005,43(12):2666-2674
Copolymers of a liquid crystalline monomer, 2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene (MPCS), with St and MMA were prepared by free radical polymerization at low conversion in chlorobenzene with 2,2′‐azobisisobutyronitrile (AIBN) as initiator. The copolymers of poly(MPCS‐co‐St) and poly(MPCS‐co‐MMA) were characterized by 1H NMR and GPC. The monomer reactivity ratios were determined by using the extended Kelen–Tudos (EKT) method. Structural parameters of the copolymers were obtained from the possibility statistics and monomer reactivity ratios. The influence of MPCS content in copolymers on the glass transition temperatures of copolymers was investigated by DSC. The thermal stabilities of the two copolymer systems increased with an increase of the molar fraction of MPCS in the copolymers. The liquid crystalline behavior of the copolymers was also investigated using DSC and POM. The results revealed that the copolymers with high MPCS molar contents exhibited liquid crystalline behaviors. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2666–2674, 2005 相似文献