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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

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.

STRESS-INDUCED CRYSTALLIZATION OF POLYURETHANE/MONTMORILLONITE NANOCOMPOSITE

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chinese Journal of polymer science 2002年第5期20卷 481-483页

作者： Xin-hua Dai Xiang-dong luo Qun Gu Xiao-li Zhang de-yan Shen Liang-he Shi Jian Xu state key laboratory of polymer physics and Chemiscy 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 and Chemistry 北京 100080

Exfoliated polyurethane/montmorillonite nanocomposites with both high elongation at break and high tensilestrength were studied by dynamic-infrared spectroscopy (dynamic-IR). The results show that crystallization indu... 详细信息

关键词： PU/montmorillonite nanocomposite dynamic-IR crystallization

CRYSTALLIZATION KINETICS OF HOMOGENEOUS AND HETEROGENEOUS LLDPE

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chinese Journal of polymer science 2002年第4期20卷 339-345页

作者： Hong-xiang Teng Wen-hong Tang Yi Shi Xi-gao Jin state key laboratory of polymer physics and chemistry center for molecular science, institute of chemistry chinese academy of sciences beijing 100080 china department of chemistry Jilin University Changchun 130023, china center for molecular science Institute of Chemistry Chinese Academy of Sciences State Key Laboratory of Polymer Physics and Chemistry 北京 100080 department of chemistry Jilin University Changchun 130023

Based on thermal analysis, the isothermal and nonisothemal crystallization kinetics of Ziegler-Natta catalyzed linear low density polyethylene (Z-N LLDPE) and metallocene catalyzed LLDPE (m-LLDPE) were studied. Treating the results with the Avrami equation and the Ozawa equation, the crystallization constant Igk and the Avrami exponent n were obtained. Some other crystallization parameters were also discussed. According to the different characteristics of the chain structures of Z-N LLDPE and metallocene LLDPE, their crystallization behaviors were analyzed. It is indicated that the homogeneity and heterogeneity of the two polymers act in different way during the crystallization process of polymers, including the nucleation and the growth of crystals under various conditions.

关键词： crystallization kinetics homogeneity heterogeneity LLDPE

MORPHOLOGICAL STUDY ON THE ORIENTED CHITOSAN FILM OBTAINED FROM PRE-SHEARED LIQUID CRYSTALLINE SOluTION IN DICHLOROACETIC ACID

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chinese Journal of polymer science 2001年第4期19卷 385-390页

作者： Zhong-ming Hu Li-heng Wu Da-cheng Wu Shou-xi Chen state key laboratory of polymer physics and chemistry, center for molecular science, institute of chemistry chinese academy of sciences, beijing 100080, china china Textile academy beijing 100025, china Textile College, Sichuan University Chengdu 610065, china 中科院化学所高分子物理与化学国家重点实验室北京中国纺织研究院北京四川大学四川成都

The oriented chitosan films obtained from pre-sheared liquid crystalline chitosan/dichloroacetic acid (DCA) solutions were studied by means of polarized optical microscopy (POM), scanning electron microscopy (SEM), infra-red dichroism technique and wide angle X-ray diffraction (WAXD). The sheer induced band texture in the film was found to correspond to the sinusoidal fibrillar microstructure along the shearing direction on the basis of POM and SEM observations. The sinusoidal fibril was found to be lying within the film plane. The model of chitosan molecular orientation in the pre-sheared film with band texture can be established assuming that the main chain orients in the shearing direction and the side group is perpendicular to the shearing direction. The WAXD azimuthal scanning at 2 theta = 20 degrees indicates that the (002) plane orients perpendicular to the shearing direction.

关键词： chitosan morphology orientation shear induced band texture liquid crystalline solution