检索结果-南通市图书馆

coil to globule transition of homo- and block-copolymer with different topological constraint and chain stiffness

在线全文

学校读者我要写书评

暂无评论

Science China Chemistry 2015年第9期58卷 1471-1477页

作者： Wei Wang Yanchun Li Zhongyuan Lu State Key Laboratory of Supramolecular Structure and Materials Institute of Theoretical Chemistry Jilin University

In this paper, we present the coil-to-globule(CG) transitions of homopolymers and multiblock copolymers with different topology and stiffness by using molecular dynamics with integrated tempering sampling method. The sampling method was a novel enhanced method that efficiently sampled the energy space with low computational costs. The method proved to be efficient and precise to study the structural transitions of polymer chains with complex topological constraint, which may not be easily done by using conventional Monte Carlo method. The topological constraint affects the globule shape of the polymer chain, thus further influencing the CG transition. We found that increasing the topological constraint generally decreased CG transition temperature for homopolymers. For semiflexible chains, an additional first-order like symmetry-broken transition emerged. For block copolymers, the topological constraint did not obviously change the transition temperature, but greatly reduced the energy signal of the CG transition.

关键词： coil-to-globule transition topological constraint chain stiffness molecular dynamics

The phase behaviour of single polyethylene chains with and without fixing one end

在线全文

学校读者我要写书评

暂无评论

Chinese Physics B 2008年第8期17卷 3115-3122页

作者：苏加叶章林溪 Department of Physics Zhejiang University Department of Physics Wenzhou University

The phase behaviour of a single polyethylene chain is studied by using molecular dynamics simulations. A free chain and a chain with fixing one end are considered here, since the atomic force microscope （AFM） tip can play a significant role in polymer crystallization in experiment. For a free chain, it is confirmed in our calculation that the polymer chain exhibits an extended coil state at high temperatures, collapses into a condensed state at low temperatures, i.e. the coil-to-globule transition that is determined by a high temperature shoulder of the heat capacity curve, and an additional liquid-to-solid transition that is described by a low temperature peak of the same heat curve. These results accord with previous studies of square-well chains and Lennard-Jones homopolymers. However, when one of the end monomers of the same chain is fixed the results become very different, and the chain cannot reach an extended coil-like state as a free chain does at high temperatures, i.e. there exists no coil-to-globule-like transition. These results may provide some insights into the influence of AFM tip when it is used to study the phase behaviour of polymer chains. If the interaction force between AFM tip and polymer monomers is strong, some monomers or one of them can be seen as being fixed by the tip, which is similar to our simulation model, and it is also found that AFM tip could induce polymer crystallization.

关键词： molecular dynamics simulations coil-to-globule transition polyethylene chains

THE ■-STATE OF A SINGLE HOMOPOLYMER CHAIN IN SOLUTION

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Polymer Science 1999年第4期17卷 367-370页

作者：吴奇 Department of Chemical Physics The Open Laboratory for Bond Selective Chemistry University of Science and Technology of China Hefei 230026 China Department of Chemistry The Chinese University of Hong Kong Shatin N. T. Hong Kong China

It has been an established practice to estimate the Θ-temperature of a polymer solution from thedisappearance of the interchain interactions (A_2 = 0) Recently, in studies of the temperature dependence ofthe chain conformation in solution, we found that the change of the chain conformation clearly underwentthree different stages which could be viewed as the 'gas'. 'liquid' and 'solid' states in terms of the freedomof the 'blobs' on the chain. The transition temperature between the first and second stages corresponds nicelyto the Θ-temperature determined by the conventional method. It reveals, for the first time, that the Θ-temperature can be deduced from the conformation change of a single polymer chain in solution, which isimportant not only in conception, but also in practice.

关键词： O-state coil-to-globule transition Poly(N-isopropylacrylamide)

聚合物A/B共混理论:相平衡及coil-to-globule转变

在线全文

学校读者我要写书评

暂无评论

聚合物A/B共混理论:相平衡及Coil-to-Globule转变