聚合物纳米球结晶机理的计算机模拟  

Computer simulation study on crystallization mechanism of polymer nano-globules

作　　者：王思邈 陶晓芳[3,4] 石静[3,4] 孔滨[1,2] 余翔 刘文志[3,4] 聂峰光 李晓霞[3,4] 杨小震[1,2] 

机构地区：[1]分子科学国家实验室 [2]中国科学院化学研究所高分子物理与化学实验室,北京100190 [3]多相复杂系统国家重点实验室 [4]中国科学院过程工程研究所,北京100190

出　　处：《中国科学：化学》2013年第1期49-54,共6页SCIENTIA SINICA Chimica

基　　金：国家自然科学基金(20874107,21073195);多相复杂系统国家重点实验室开放项目基金的资助

摘　　要：本文基于位置有序参数(SOP)分析了利用图形处理器(GPU)加速的分子动力学程序GMD模拟含有4.5万和36万个CH2联合原子的聚乙烯纳米球的分子动力学结晶过程中结晶度的变化,并使用Avrami方程得到了不同温度下的结晶指数.与一般实验结果相同,该指数n不为整数.我们提出了二元混合模型,认为纳米线团的结晶行为由两种机理按一定比例组成.当结晶温度升高时,两种尺寸的纳米线团的Avrami指数均升高并接近4,结晶机理趋向三维生长和均相成核.当温度低时,晶核多在接近纳米球的表面生成,Avrami指数趋近于1.我们对体系结晶成核阶段结束时晶核沿纳米球的径向分布进行了分析.结果表明Tn=0.60时晶核的生成位置接近表面,而Tn=0.68时晶核出现一个接近纳米球内部的峰.该结果与二元混合模型的Avrami指数的分析结果相吻合.Based on the site order parameter （SOP）, the present study analyzed molecular dynamics trajectory data of crystallinity evolution of polyethylene nano-globules with 45,000 or 360,000 united atoms of CH2 using GMD, a GPU enabled program of molecular dynamics. According to Avrami equation, Avrami exponents n, at various temperatures were obtained. As those obtained from most experiments, the exponents are not integers. In explanation of the non-integer result, we thus proposed a binary model that in one system there exist two crystallization mechanisms with two integers of Avrami exponents. We found that when temperature rises up, Avrami exponents of both nano-globules increase up to 4. The crystallization approaches the mechanism which is in homogenous nucleation and 3-dimensional growth. When the temperature falls down, most of the nuclei come into the area close to the surface of the globule, and Avrami exponents decrease to 1. We also found that nucleus distribution along the radius of the globules is various with temperature. Results show that the nuclei are located close to the surface when Tn = 0.60, while the nuclei appear near inner range as well when Tn = 0.68. This result supports the analysis of Avrami exponents in the binary model.

关 键 词：聚乙烯纳米球 高分子结晶 Avrami方程 分子动力学 图形处理器(GPU) 

分 类 号：TB383.1[一般工业技术—材料科学与工程]