胡文兵
高分子结晶学及其相关的物理化学问题,以分子水平上的格子理论和蒙特卡罗模拟研究为主,辅以温度调制式差热分析技术及其它物理表征手段。
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- 姓名:胡文兵
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学术头衔:
博士生导师
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学科领域:
高分子化学
- 研究兴趣:高分子结晶学及其相关的物理化学问题,以分子水平上的格子理论和蒙特卡罗模拟研究为主,辅以温度调制式差热分析技术及其它物理表征手段。
胡文兵,男,汉族,南京大学化学化工学院教授。1966年出生,1989年本科毕业于复旦大学材料科学系高分子材料科学与工程专业,1995年博士毕业于复旦大学高分子科学系高分子化学与物理专业,导师于同隐教授,其后留校任教,主讲本科生“高分子物理”和研究生“高分子结晶与结构”课程,分别于1998-1999年赴德国弗莱堡大学物理系Strobl研究组、2000-2001年美国田纳西大学化学系Wunderlich研究组、2001-2003年荷兰物质科学研究院(FOM)原子与分子物理研究所Frenkel研究组从事博后研究,2004年到南京大学任教至今。主要研究方向:高分子结晶学及其相关的物理化学问题,以分子水平上的格子理论和蒙特卡罗模拟研究为主,辅以温度调制式差热分析技术及其它物理表征手段。
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胡文兵
,-0001,():
-1年11月30日
从高分子的主要物理行为与分子结构之间已知的、内在的本质对应关系出发,初步勾勒出一个简单的包含高分子物理基础教学中所要求介绍的大多数基本概念的逻辑框架,即以两个共性特征和3个个性特征来描述高分子的基本结构,以便理顺高分子结构与性质之间的对应关系,在较短的时间内达到更好的教学效果。
高分子科学,, 链结构,, 结构与性质之间的对应关系
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胡文兵, Maoxiang Wang, †, Wenbing Hu, *, ‡, Yu Ma, ‡ and Yu-qiang Ma†
Macromolecules 2005, 38, 2806-2812,-0001,():
-1年11月30日
We studied the athermal relaxation of bulk extended chains and the isothermal crystallization in an intermediately relaxed melt by means of dynamic Monte Carlo simulations of latticepolymer systems. The melt contained a memory of chain orientations but no more crystalline order. We found that the athermal relaxation is continuous and homogeneous among the bulk chains, and its rate depends on the chain length. The orientational memory in the melt significantly enhances the rate of rystallization. Nevertheless, no precursor of crystallization occurs in the melt of uniform chain lengths. But, in a binary blend of different chain lengths, the crystallization of oriented long chains acts as the precursor to induce epitaxial crystallization of the relaxed short chains. This mechanism explains the formation of shish-kebab crystals observed frequently in the processing of semicrystalline polymers. The results suggest that in flow-induced polymer crystallization the orientational relaxation of chains decides a selection of the long-chain component and then the precursor formation.
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【期刊论文】Chain folding in polymer melt crystallization studied by dynamic Monte Carlo simulations
胡文兵, Wenbing Hu
J. Chem. Phys., Vol. 115, No. 9, 1 September 2001,-0001,():
-1年11月30日
The morphological metastability of spontaneous crystallization from the melt of short-chain semiflexible homopolymers was studied through dynamic Monte Carlo simulations of a lattice multiple-chain system. Frictional hindrance for the sliding diffusion of the chains in the crystallites was employed to enhance the metastability of folded-chain crystallites, and distinguish the polymer crystallite from its mesophase, though their phase transitions have the similar driving forces. The integral folding of short chains in the crystallites and the constant linear crystal growth rate were identified with the actual polymers. In addition, the roughness of the local growth front accompanied with the occasional reversals and jumplike advancing was observed, which cannot be explained by current models. The crowding of the dangling ends on the fold surface seems to be the main reason for suppressing the lateral growth front, and the mechanism of chain folding was proposed. Its implications to the special behaviors of polymer melt crystallization, such as the semicrystalline state, the effect of the chain rigidity and molecular weight to crystal growth, the reversible premelting, and molecular segregation are briefly discussed.
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【期刊论文】Simulation of Shish-Kebab Crystallite Induced by a Single Prealigned Macromolecule
胡文兵, Wenbing Hu, † Daan Frenkel, *, † and Vincent B. F. Mathot‡
Macromolecules 2002, 35, 7172-7174,-0001,():
-1年11月30日
Crystal nucleation is an activated process. In a supersaturated solution, small crystallites may dissolve again. Crystals can only be formed when a (rare) fluctuation leads to the formation of a crystallite with a size that exceeds a threshold. The probability to form such a "critical" crystal nucleus is determined by its excess free energy. For a simple molecular crystal, 1 the free energy change for forming a small crystallite from the liquid is approximately given by
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【期刊论文】Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations
胡文兵, Wenbing Hu, *, †, Vincent B. F. Mathot, ‡ and Daan Frenkel†
Macromolecules 2003, 36, 2165-2175,-0001,():
-1年11月30日
We report a numerical study of crystallization and melting in bulk statistical homogeneous (random), homogeneous (slightly alternating), and heterogeneous (produced in a batch reaction) copolymers formed by crystallizable monomers and noncrystallizable comonomers. In our dynamic Monte Carlo simulations of lattice chains, the current model further assumes that the comonomers cannot move into crystalline regions by sliding diffusion of the chains. We find that both the overall composition and the statistical distribution of the monomers affect the phase-transition temperature, the resulting relative crystallinity, and the crystal morphology. However, the final absolute crystallinity of homogeneous copolymers seems insensitive to these parameters. Intramolecular segregation between monomers and comonomers is accompanied by crystallization, demonstrating the concept of sequence segregation or nanophase separation of statistical copolymers with assembling structures like in thermoplasticelastomers. Moreover, if crystallization of homogeneous copolymers has started but not yet completed on cooling, subsequent heating will show cold crystallization before melting, which can be attributed to insertion-mode lamellar growth. For heterogeneous copolymers, intermolecular segregation occurs on cooling before crystallization. On the basis of our observations, a pair of master melting and crystallization curves for the crystallinity of a statistical copolymer as a function of temperature are suggested to reflect the characteristic of the monomer-sequence-length distribution. This suggestion facilitates the clarification to the kinetic disturbance in local temperature regions and to the principle of some fractionation methods, such as temperature rising elution fractionation (TREF).
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【期刊论文】Intramolecular Nucleation Model for Polymer Crystallization
胡文兵, Wenbing Hu, *, †, Daan Frenkel, † and Vincent B. F. Mathot‡
Macromolecules 2003, 36, 8178-8183,-0001,():
-1年11月30日
We report a numerical study of the free energy barrier for crystallization and melting of a single homopolymer chain. The simulations show that the free energy barrier separating the crystalline and molten states at the same free energy level strongly depends on the chain length. However, at a fixed temperature the barrier for single-chain crystallization is independent of chain length. This observation is in agreement with recent experiments on multichain bulk-polymer systems and can be understood theoretically if we assume that the primary nucleation of polymer crystals is determined by intramolecular nucleation. If we further assume that the subsequent growth of polymer crystals is controlled by two-dimensional intramolecular nucleation on the growth front, we can even account for the experimentally observed molecular segregation during crystal growth as well as the chain-length independence of the free energy barrier for secondary nucleation.
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胡文兵, Wenbing Hu a), Vincent B. F. Mathot
J. Chem. Phys., Vol. 119, No. 20, 22 November 2003,-0001,():
-1年11月30日
On the basis of an extended Flory-Huggins expression for the mixing free energy of the long-chain binary polymer blend, we showed that liquid-liquid demixing can be driven solely by the propensities of crystallization differing with respect to components. Demixing prior to crystallization on cooling was demonstrated by dynamic Monte Carlo simulations of the lattice model for a symmetric polymer blend where only one component is crystallizable.We discussed the implications of this principle to several experimental observations including the (in) compatibility of polymer chains with different stereochemical compositions, the memory effect of polymer crystallization, and the spinodal decomposition at an early stage of polymer crystallization.
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胡文兵, Wenbing Hu and Daan Frenkela), Vincent B. F. Mathot
J. Chem. Phys., Vol. 118, No. 22, 8 June 2003,-0001,():
-1年11月30日
We report Monte Carlo simulations of a lattice-polymer model that can account for both polymer crystallization and liquid-liquid demixing in solutions of semiflexible homopolymers. In our model, neighboring polymer segments can have isotropic interactions that affect demixing, and anisotropic interactions that are responsible for freezing. However, our simulations show that the isotropic interactions also have a noticeable effect on the freezing curve, as do the anisotropic interactions on demixing. As the relative strength of the isotropic interactions is reduced, the liquid-liquid demixing transition disappears below the freezing curve. A simple extended Flory-Huggins theory accounts quite well for the phase behavior observed in the simulations.
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【期刊论文】The melting point of chain polymers
胡文兵, Wenbing Hu a)
J. Chem. Phys., Vol. 113, No. 9, 1 September 2000,-0001,():
-1年11月30日
Based upon a consideration of the similarity in the driving force of polymer crystallization to the mesophase formation from the melt state, the equilibrium melting point of chain polymers relating to the details of molecular structure and the impure environment of crystallites was studied by classical lattice statistics and dynamic Monte Carlo simulations. The compact packing energy change of local chains during crystallization can be represented as an orientation-dependent attraction in the lattice model. The results as a function of driving force, chain length, content of random comonomers, and content of the diluent like small molecules or noncrystalline chains were compared with the semiempirical expressions that have been verified for several polymers. Good agreements were obtained. As a result, the classical lattice statistics can predict a disorder-order phase transition as well as a phase separation behavior in a mixture system containing polymers, and supply the thermodynamic background to explore details of these behaviors in computer simulations.
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【期刊论文】Oriented primary crystal nucleation in lamellar diblock copolymer systems
胡文兵, Wenbing Hu and Daan Frenkel
Faraday Discuss., 2005, 128, 253-260,-0001,():
-1年11月30日
We report a numerical study of the primary crystal nucleation of diblock copolymers in a lamellar phase. Only one of two polymer blocks is crystallizable; the other is maintained in a glassy state. We find that crystals in this lamellar geometry tend to nucleate with the chain axis perpendicular to the lamellar plane. However, if in the same lamellar structure, we break the junction between the crystallizable and non-crystallizable blocks of the olymers, we find that crystallites tend to align parallel to the lamellar plane. This observation clarifies the molecular origin of the competition between parallel and perpendicular crystallite orientations in real block-copolymer systems.
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