Kos Pavel I, Ivanov Viktor A, Chertovich Alexander V
Faculty of Physics, Lomonosov Moscow State University, 119991 Moscow, Russia.
Soft Matter. 2021 Mar 11;17(9):2392-2403. doi: 10.1039/d0sm01545h.
We studied the crystallization of semiflexible polymer chains in melts and poor-solvent solutions with different concentrations using dissipative particle dynamics (DPD) computer simulation techniques. We used the coarse-grained polymer model to reveal the general principles and microscopic scenario of crystallization in such systems at large time and length scales. It covers both primary and secondary nucleation as well as crystallites' merging. The parameters of the DPD model were chosen appropriately to reproduce the entanglements of polymer chains. We started from an initial homogeneous disordered solution of Gaussian chains and observed the initial stages of crystallization process caused in our model by orientational ordering of polymer chains and polymer-solvent phase separation. We found that the overall crystalline fraction at the end of the crystallization process decreases with the increasing polymer volume fraction while the steady-state crystallization speed at later stages does not depend on the polymer volume fraction. The average crystallite size has a maximal value in the systems with a polymer volume fraction from 0.7 to 0.95. In our model, these polymer concentrations represent an optimal value in the sense of balance between the amount of polymer material available to increase the crystallite size and chain entanglements, that prevent crystallites' growth and merging. On large time scales, our model allows us to observe lamellar thickening linear in logarithmic time scale.
我们使用耗散粒子动力学（DPD）计算机模拟技术，研究了不同浓度的半柔性聚合物链在熔体和不良溶剂溶液中的结晶过程。我们采用粗粒化聚合物模型，以揭示此类系统在长时间和大长度尺度下结晶的一般原理和微观过程。该模型涵盖了初级和次级成核以及微晶的合并。我们适当选择了DPD模型的参数，以重现聚合物链的缠结。我们从高斯链的初始均匀无序溶液开始，观察了模型中由聚合物链的取向有序化和聚合物 - 溶剂相分离引起的结晶过程的初始阶段。我们发现，结晶过程结束时的总结晶分数随聚合物体积分数的增加而降低，而后期的稳态结晶速度则不依赖于聚合物体积分数。在聚合物体积分数为0.7至0.95的系统中，平均微晶尺寸具有最大值。在我们的模型中，从增加微晶尺寸可用的聚合物材料量与防止微晶生长和合并的链缠结之间的平衡角度来看，这些聚合物浓度代表了一个最佳值。在长时间尺度上，我们的模型使我们能够观察到在对数时间尺度上呈线性的片晶增厚现象。
