Department of Applied Physics, National Defense Academy, Yokosuka 239-8686, Japan.
Faculty of Materials Science and Engineering, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan.
J Chem Phys. 2019 Feb 21;150(7):074901. doi: 10.1063/1.5080332.
To investigate crystallinities based on trans-structures, we determined the differences in the crystallization properties of ring and linear polymers by performing united-atom-model molecular dynamics (MD) simulations of homogeneous polyethylene melts of equal length, N, which refers to the number of monomers per chain. Modified parameters based on the DREIDING force field for the CH units were used in order to accelerate the crystallization process. To detect polymer crystallization, we introduced some local-order parameters that relate to trans-segments in addition to common crystallinities using neighboring bond orders. Through quenching MD simulations at 5 K/ns, we roughly determined temperature thresholds, T, at which crystallization is observed although it was hard to determine the precise T as observed in the laboratory time frame with the present computing resources. When N was relatively small (100 and 200), T was determined to be 320 and 350 K for the linear- and ring-polyethylene melts, respectively, while T was found to be 330 and 350 K, respectively, when N was 1000. Having confirmed that the crystallization of a ring-polyethylene melt occurs faster than that of the analogous linear melt, we conclude that the trans-segment-based crystallinities are effective for the analysis of local crystal behavior.
为了研究基于反式结构的结晶度，我们通过对等长、N（指每条链上的单体数）的均聚聚乙烯熔体进行统一原子模型分子动力学（MD）模拟，来确定环状和线状聚合物的结晶性能差异。为了加速结晶过程，我们使用了基于 Dreiding 力场的 CH 单元的修改参数。除了常用的结晶度外，我们还通过引入一些与反式片段相关的局部有序参数来检测聚合物结晶。通过在 5 K/ns 下进行淬火 MD 模拟，我们大致确定了观察到结晶的温度阈值 T，尽管很难像实验室时间框架那样使用当前的计算资源来确定精确的 T。当 N 较小时（100 和 200），线性和环状聚乙烯熔体的 T 分别确定为 320 和 350 K，而当 N 为 1000 时，T 分别为 330 和 350 K。我们确认了环状聚乙烯熔体的结晶速度快于类似的线性熔体，因此得出结论，基于反式片段的结晶度对于分析局部晶体行为是有效的。
