Physics Department, Lomonosov Moscow State University, Leninskie gory, 1, build. 2, 119991 Moscow, Russia.
Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninsky prosp. 29, 119991 Moscow, Russia.
J Chem Phys. 2013 Dec 14;139(22):224901. doi: 10.1063/1.4837215.
Phase diagrams for monodisperse and polydisperse diblock copolymer melts and a random multiblock copolymer melt are constructed using dissipative particle dynamics simulations. A thorough visual analysis and calculation of the static structure factor in several hundreds of points at each of the diagrams prove the ability of mesoscopic molecular dynamics to predict the phase behavior of polymer systems as effectively as the self-consistent field-theory and Monte Carlo simulations do. It is demonstrated that the order-disorder transition (ODT) curve for monodisperse diblocks can be precisely located by a spike in the dependence of the mean square pressure fluctuation on χN, where χ is the Flory-Huggins parameter and N is the chain length. For two other copolymer types, the continuous ODTs are observed. Large polydispersity of both blocks obeying the Flory distribution in length does not shift the ODT curve but considerably narrows the domains of the cylindrical and lamellar phases partially replacing them with the wormlike micelle and perforated lamellar phases, respectively. Instead of the pure 3d-bicontinuous phase in monodisperse diblocks, which could be identified as the gyroid, a coexistence of the 3d phase and cylindrical micelles is detected in polydisperse diblocks. The lamellar domain spacing D in monodisperse diblocks follows the strong-segregation theory prediction, D∕N(1∕2) ~ (χN)(1∕6), whereas in polydisperse diblocks it is almost independent of χN at χN < 100. Completely random multiblock copolymers cannot form ordered microstructures other than lamellas at any composition.
使用耗散粒子动力学模拟构建了单分散和多分散两嵌段共聚物熔体以及无规多嵌段共聚物熔体的相图。在每个相图的几百个点中的几个点上进行了彻底的可视化分析和静态结构因子的计算，证明了介观分子动力学能够像自洽场理论和蒙特卡罗模拟一样有效地预测聚合物体系的相行为。结果表明，单分散两嵌段的有序-无序转变（ODT）曲线可以通过均方压力涨落对 χN 的依赖性中的尖峰来精确定位，其中 χ 是 Flory-Huggins 参数，N 是链长。对于另外两种共聚物类型，观察到了连续的 ODT。长度上遵循 Flory 分布的两个嵌段的大多分散性不会移动 ODT 曲线，但会显著缩小圆柱相和层状相的区域，分别用蠕虫状胶束和穿孔层状相部分取代。在单分散两嵌段中，可以识别为向列型的纯 3d 双连续相，在多分散两嵌段中检测到 3d 相和圆柱胶束的共存。单分散两嵌段中的层状畴间距 D 遵循强分离理论预测，D∕N(1∕2)~(χN)(1∕6)，而在多分散两嵌段中，在 χN < 100 时，它几乎与 χN 无关。完全无规的多嵌段共聚物在任何组成下都不能形成除层状以外的有序微结构。
