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TRANSIENT EFFECT OF A BOGER FluID FLOWING AROUND A CONFINED CYLINdeR

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chinese Journal of polymer science 2001年第4期19卷 377-384页

作者： Xian-feng Li Huai-tian Bu de-lu zhao state key laboratory of polymer physics and chemistry center for molecular science,institute of chemistry, chinese academy of sciences, beijing 100080, china 中科院化学所高分子物理与化学国家重点实验室北京

This paper is concerned with the numerical simulation of the transient effect of an inertialess Boger flow past a confined circular cylinder and the comparison of predictions with particle image velocimetry (PIV) measurements given by Shiang et al.. Dynamic simulation based on the Oldroyd-B constitutive model was carried out using a Lagrangian-Eulerian algorithm. The evolution of velocity field was obtained for the flow at two deborah (de) numbers, i.e. de = 1.2 and 3.0. At low de, the flow reached steady state rapidly, and showed a symmetric flow regime. However, at high de, the time required to reach steady flow behind the cylinder increased significantly, and the distribution of the velocity field appears to be asymmetric with respect to the stagnation line. Fairly good agreement between the numerical results and the experimental observations is reported. It can be concluded that both the experimental measurements and the present simulations indicate that the elasticity of the polymeric flow strongly affect the flow regime of viscoelastic flow around a confined cylinder.

关键词： transient effect flow around a cylinder Lagrangian-Eulerian algorithm Oldroyd-B model

PREPARATION OF BISPHENOL A EPOXY RESIN WATERBORNE DISPERSIONS BY THE PHASE INVERSION EMULSIFICATION TECHNIQUE

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chinese Journal of polymer science 2000年第1期18卷 33-38页

作者： Zhen-zhong Yang de-lu zhao polymer physics laboratory, institute of chemistry, chinese academy of sciences, beijing 100080, china 中科院化学所高分子物理及化学国家重点实验室北京

The phase inversion emulsification technique (PIET) is an effective physical method for preparing waterborne dispersions of polymer resins. Some results concerning the preparation of bisphenol A epoxy resin waterborne dispersions by PIET in our laboratory were summarized. Electrical properties, rheological behavior and morphological evolution during phase inversion progress were systematically characterized. The effects of the emulsifier concentration and emulsification temperature on phase inversion progress and the structural features of the waterborne particles were studied as well. The deformation and break up of water drops in a shear field were analyzed in terms of micro-theology, while the interaction and coalescence dynamics of water drops were discussed in terms of DLVO theory and Smoluchowski effective collision theory, respectively. Based on the experimental results and theoretical analysis, a physical model of phase inversion progress was suggested, by which the effects of the parameters on phase inversion progress and the structural features of the waterborne particles were interpreted and predicted.

关键词： phase inversion emulsification waterborne dispersions epoxy resin mechanism physical model

EFFECT OF PARTICLE SIZE ON THE FILMING PROCESS OF POLYSTYRENE LATEX STUDIED BY AFM

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chinese Journal of polymer science 2002年第6期20卷 509-515页

作者： Xiao-zhong Qu Yi Shi Liu-sheng Chen Xi-gao Jin state key laboratory of polymer physics & chemistry, center for molecular science,institute of chemistry, chinese academy of sciences, beijing 100080 china state key Lab. of polymer Phy./Chem. Institute of Chemistry Chinese Academy of Sciences Beijing 100080 China

The film formation process of micro-PS particles (diameter 742 nm) and nano-PS particles (diameter 29 nm) was studied by atomic force microscopy and differential scanning calorimetry. During a step heating process, the particles were annealed for 0.5 h at each selected temperature. It was found that the deformation and interdiffusion temperatures of the micro-PS particles are ca. 120-130degreesC and 140-150degreesC, that of the nano-PS particles are 90degreesC and 100-110degreesC respectively. The DSC traces of nano-PS particles showed that there was an exothermic peak near T-g after annealing for 0.5 h at the selected temperatures below 90degreesC; otherwise, the exothermic peak disappeared after annealing at 100degreesC or above. Compared with the micro-PS particles, the sintering process of nano-PS particles occurs at much lower temperature determined by the confined state of polymer chains with higher conformational energy in nano-particles, and completes in a much narrower temperature range driven mainly by the larger total surface energy.

关键词： polystyrene latex filming process particle size effect

VISCOELASTIC BEHAVIOR OF THE NON-HOOKE deFORMATION BEFORE YIELDING IN UNIAXIAL DRAWING OF AMORPHOUS POLY(ETHYLENE TEREPHTHALATE)

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chinese Journal of polymer science 2001年第4期19卷 399-405页

作者： Zhen-hua Yuan de-yan Shen Ren-yuan Qian polymer physics laboratory center for molecular science, institute of chemistry chinese academy of sciences, beijing 100080 china 中科院化学所高分子物理及化学国家重点实验室北京

Viscoelastic behavior of the non-Hooke deformation of amorphous PET film before yield was investigated in the temperature region 74-80.5 degreesC around the glass transition temperature. The film specimen was drawn to yield point followed by unloading to zero stress, then the residual deformation was held constant; while the subsequent evolution of the stress was recorded. An induction period was found in the course of stress evolution followed by a stress step-increase. The induction period decreases with increasing drawing temperature with an activation energy of 1.10 MJ/mol.K, which is attributed to the time needed for the relaxation of rubbery deformation through cooperative internal rotations. At temperatures lower than 74 degreesC, there is no stress increase or the induction period becomes too long to be observed. Thus the nature of anelasticity in the non-Hooke region before yielding is attributed to stress induced rubbery deformation. The experimental results are interpreted in terms of Perez' theological model of a series connected Hooks spring and a Voigt element consisting of a parallel connected elastic spring and a dashpot.

关键词： pre-yield deformation PET uniaxial drawing non-Hooke deformation viscoelasticity stress induced rubbery deformation

molecular SIMULATION STUDY ON THE CHANGE OF polymer STRUCTURE DURING YIELDING

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chinese Journal of polymer science 2001年第5期19卷 527-529页

作者： Chen-guang Xu Tai-ning Liang Juan Sun Xiao-zhen Yang state key laboratory of polymer physics and chemistry center for molecular science, institute of chemistry chinese academy of sciences, beijing 100080 china 中科院化学所高分子物理与化学国家重点实验室北京

A better understanding of a recently raised argument on whether there occurs a structure change during yielding has been acquired by using molecular simulation. That is, when monitoring the displacements of all atoms before and after the yield, a structure transition does occur, which is the 'atomic jump' that coordinates the amount of the atoms in the polymer and makes a large step beyond similar to0.05 nm for all those atoms. Results indicate that the complex of polymer chain packing induces the multiple atomic jumps around the yield point. This explains why polymers have a broader yielding peak.

关键词： polymer deformation yield structure transition atomic jump multiple yields

STUDY ON PYROLYSIS OF POLYPHENYLSILSESQUIOXANE

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chinese Journal of polymer science 2002年第6期20卷 573-577页

作者： Jun Ma Liang-he Shi Jian-min Zhang Bai-yu Li de-yan Shen Jian Xu state key laboratory of polymer physics & chemistry center for molecular science, institute of chemistry,chinese academy of sciences, beijing 100080 china center for molecular science Institute of Chemistry Chinese Academy of Sciences State Key Laboratory of Polymer Physics & Chemistry 北京 100080

X-ray photoelectron spectroscopy and Raman spectroscopy were' used to determine the chemical change of polyphenylsilsesquioxane (PPSQ) during pyrolysis in flowing nitrogen. Two temperature ranges were found for pyrolysed PPSQ below and above 600degreesC, respectively. The former is related to the rearrangement of PPSQ backbone and the latter reflects that most of backbone structure of PPSQ might be broken down and unorganized. Carbon formed in carbonization of PPSQ sample pyrolysed at 900degreesC should be sp(3) bonded carbon with crystallite size effects or defects.

关键词： pyrolysis polyphenylsilsesquioxane

Relaxation of Chain Extension of Amorphous PET Fiber Above the Glass Transition Temperature

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chinese Chemical Letters 2000年第10期11卷 925-928页

作者： Xin LINGHU, Jun zhao, Rui SONG, Qing Rong FAN (polymer physics laboratory, center of molecular science, institute of chemistry, chinese academy of sciences, beijing, 100080) polymer physics laboratory Center of Molecular Science Institute of Chemistry Beijing 100080 China

The recovery of amorphous PET fiber in global chain orientation but nearly random segmental orientation (GOLR) state was studied by the hot shrinkage measurement above the glass transition temperature. The relaxation curves in the form of di-exponential decay were acquired and the change of two special times with the variation of treating temperature and residual recovery ratio ' was discussed.

关键词： GOLR state PET recovery of chain extension hot shrinkage measurement.

COALESCENCE INDUCED GRADIENT MORPHOLOGY NEAR A WALL IN PHASE SEPARATED polymer BLENDS DURING QUIESCENT ANNEALING

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chinese Journal of polymer science 2002年第6期20卷 543-550页

作者： Wei Yu Chi-xing Zhou de-lu zhao department of polymer science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 china state key laboratory of polymer physics and chemistry, institute of chemistry, chinese academy of sciences beijing 100080, china department of polymer science and Engineering Shanghai Jiao Tong University 上海 200240 institute of chemistry Chinese Academy of Sciences State Key Laboratory of Polymer Physics and Chemistry 北京 100080

A fast coalescence mechanism is proposed to account for the wall effect on the formation of gradient morphology in phase separated polymer blends during quiescent annealing. The existence of solid wall with high polarity is believed to change the potential field around the dispersed particles near the wall. This additional potential interaction between the solid wall and the dispersed particles causes faster coalescence of the dispersed particles near the wall than in the bulk. The gradient phase morphology thus formed can be predicted by combining the wall-particle interaction and the touch-coalescence mechanism. The effect of interfacial tension on the gradient morphology is also discussed.

关键词： gradient morphology wall effect coalescence polymer blends interfacial tension

Interfacial behaviors of PMMA-PEO block copolymers at the air/water interface

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science china chemistry 2005年第6期48卷 567-573页

作者： CHENG Caixia1, JIAO Tifeng2, TANG Rupei1, LIU Minghua2 & XI Fu1 1. state key laboratory of polymer physics and chemistry, Joint laboratory of polymer science and Materials, institute of chemistry, chinese academy of sciences, beijing 100080, china 2. CAS key laboratory of Colloid and Interface science, institute of chemistry, chinese academy of sciences, beijing 100080, china state key laboratory of polymer physics and chemistry Joint Laboratory of Polymer Science and Materials Institute of Chemistry Chinese Academy of Sciences Beijing China CAS key laboratory of Colloid and Interface science Institute of Chemistry Chinese Academy of Sciences Beijing China

Diblock copolymer of PMMA291-b-PEO114 and triblock copolymer of PMMA120-b- PEO227-b-PMMA120 were synthesized and their interfacial properties at the air-water interface were investigated, where both blocks of polyethylene oxide (PEO) and poly(methyl methacrylate) (PMMA) are surface active but the former is soluble in water while the latter is not. Both the block copolymers could form monolayers with two obvious transition regions. The first transition point is around 10 mN/m, which could be assigned to the pancake-brush change of the PEO chains. The other is around 18 mN/m, which could be ascribed to the condensed packing of PMMA. The surface morphological changes during the compression of the Langmuir monolayers are inves-tigated by using the AFM and SEM methods for the films deposited at different surface pressure or molecular areas. At a lower surface pressure, a typical morphology of PEO-con- taining lipopolymers is observed. Upon compression, sphere-dominant morphologies were observed. While the diblock copolymer is easy to folding, the triblock copolymer is in favor of formation of circular domains through vesiculation.

关键词： PMMA-PEO, block copolymers, monolayer, Langmuir-Blodgett films, AFM.