MACROMOLECULAR ORDERING; MOLECULAR DYNAMICS OF CHAIN FOLDING

大分子，如合成聚合物、蛋白质和dna，由于其在通常的低分子质量物质中从未被研究过的新特性而引起了人们的极大关注。特别是在大分子中，有序是聚合物结晶、蛋白质折叠等过程的基本过程，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的分子过程。我们首先研究了聚合物晶体生长表面上二次成核的分子机制。我们采用了一个由500个由弹簧连接的小珠组成的聚乙烯分子的简化模型，并忽略周围的分子，考虑气相结晶。在真空条件下，在聚合物晶体的无限宽侧表面附近放置一个强折叠链，并通过分子动力学模拟研究了分子的吸附和排序过程。更重要的是，聚合物链被迅速吸附，以逐步的方式，形成层状结构：在较低的温度下是多层的，在较高的温度下是单层的。吸附在表面的链段彼此平行排列，并在几ns内逐渐生长成整齐的链折叠薄片，主要是邻接再入褶皱。晶片厚度受结晶温度的影响较大，在熔点附近迅速增大。链式分子，如正烷烃，最近被发现在液体的自由表面呈现单层或双层结构。我们还通过分子动力学模拟研究了表面结晶、单层形成、单层内和单层与持续熔融相之间的链扩散。除了这些关于聚合物有序的工作外，我们还通过实验方法和计算机模拟对聚合物晶体的结构相变进行了研究。少

Macromolecules, such as synthetic polymers, proteins, 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 processes of macromolecular ordering by experiments and computer simulations.We have first investigated the molecular mechanism of secondary nucleation on a growth surface of the polymer crystal. We adopt a simplified model of polyethylene molecule made of 500 beads connected by springs, and consider the crystallization from a vapor phase neglecting surrounding molecules. A strongly collapsed chain in a vacuum was placed near the infinitely wide lateral-surface of the polymer crystal, and the molecular processes of adsorption and ordering were investigated by molecular dynamics simulation. It was found t … More hat the polymer chain is quickly adsorbed, in a stepwise manner, to form a layer structure : a multilayered at lower temperature and a monolayered at higher temperature. The chain segments adsorbed to the surface align parallel with each other and gradually, within several ns, grow into a neat chain folded lamella with predominantly adjacent-reentry folds. The thickness of the lamella sensibly depends on the crystallization temperature and shows a rapid increase around the melting point.The chain molecules, such as n- alkanes, are recently found to show monolayers or bilayers on free surface of the liquid. We have also investigated, by molecular dynamics simulation, the surface crystallization, monolayer formation, and chain diffusion within the monolayer and between the monolayer and the sustaining melt phase.Beside these works on polymer ordering, we have made investigations on the structural phase transitions in polymer crystals both by experimental methods and by computer simulation. Less