MACROMOLECULAR ORDERING ; CHAIN FOLDING AND THE INTERFACES

大分子，如合成聚合物、蛋白质a和DNA，由于其新颖的性质而引起了人们的极大关注，这些性质对于通常的低分子量物质从未被研究过。特别是大分子有序化是高分子结晶、蛋白质折叠等过程中的一个基本过程，因此引起了人们极大的兴趣。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水平结构在研究高分子结晶过程中具有重要意义。本文用分子动力学和Monte Carlo模拟方法研究了晶体表面的结构和分子运动，发现晶体表面相当无序，分子运动大大增强。此外，在表面的无序结构被发现对应于高温结晶相。分子在表面的大迁移率应反映在晶体表面聚合物结晶的微观过程中。我们用分子动力学方法模拟了链折叠结晶过程，发现聚合物链在几纳秒内就形成了一个相当整齐的链折叠片层，链分子如正构烷烃可以形成单层或双层。近年来，人们发现正构烷烃液体具有特殊的有序表面单层结构。这种特殊的有序结构的形成机制是非常有趣的。用分子动力学模拟方法研究了正构烷烃液体的表面结构。我们发现在熔点以上几度范围内出现了特殊的有序蒙莱。

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.