MACROMOLECULAR ORDERING ; CHAIN FOLDING AND THE INTERFACES

大分子，如合成聚合物、蛋白质和DNA，由于其新颖的性质而引起了人们的极大关注，这些性质是通常的小分子物质从未研究过的。特别是大分子有序化是聚合物结晶、蛋白质折叠等的基本过程，本文通过实验和计算机模拟研究了大分子有序化的分子过程。晶体生长前沿的分子结构对考虑聚合物结晶具有重要意义。我们用分子动力学和蒙特卡罗模拟研究了晶体表面的结构和分子迁移率，发现晶体表面相当无序，分子迁移率大大提高。此外，表面的无序结构与高温晶相的无序结构相对应。表面分子的大迁移率应该反映在结晶表面聚合物结晶的微观过程中。我们用分子动力学的方法模拟了链状折叠结晶的过程，发现聚合物链在几纳秒内形成了相当整齐的链状折叠片层，链上的分子，如正构烷烃，通常形成单分子层或双分子层。近年来，人们发现正构烷烃的液体呈现出一种特殊的有序表面单层结构。这种特殊有序结构的形成从机理上来说是非常有趣的。用分子动力学模拟方法研究了正构烷烃液体的表面结构。我们发现，在高于熔点几度的范围内，出现了一种特殊的有序结构。

Macromolecules, such as synthetic polymers, proteinsa, and DNAs, have attracted great attention due to their novel properties that have never been studied for usual low molecular mass substances. Especially the macromolecular ordering is of great interest since it is a fundamental process involved in polymer crystallization, protein folding, etc. We have here investigated the molecular process of macromolecular ordering by experiments and computer simulations.A molecular level structure of the crystal growth front is of fundamental importance in considering the polymer crystallization. We here investigated, by molecular dynamics and Monte Carlo simulations, the structure and molecular mobility at the crystal surface, and found that the crystal surface is considerably disordered and that the molecular mobility is there greatly enhanced. Furthermore the disordered structure at the surface was found to correspond to that of the high temperature crystalline phase. The large mobility of the molecule at the surface should be reflected in the microscopic process of polymer crystallization at the crystal surface. We have simulated the process of chain folded crystallization by the molecular dynamics method, and we have found that the polymer chain forms a rather neat chain folded lamella within several nanoseconds.The chain molecules, such as n- alkanes, are known to form monolayrs or bilayrs. Recently, the liquid of n-alkane was found to exhibit peculiar ordered surface-monolayr. The formation of such peculiar ordered structure is very interesting with respect to its mechanism. We have investigated, by molecular dynamics simulation, the surface structure of n-alkane liquid. We have found that there appears peculiar ordered monlayr within a few degree above the melting point.