Rakshit A, Picu R C
Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, USA.
J Chem Phys. 2006 Oct 28;125(16):164907. doi: 10.1063/1.2362820.
A coarse graining procedure aimed at reproducing both the chain structure and dynamics in melts of linear monodisperse polymers is presented. The reference system is a bead-spring-type representation of the melt. The level of coarse graining is selected equal to the number of beads in the entanglement segment, Ne. The coarse model is still discrete and contains blobs each representing Ne consecutive beads in the fine scale model. The mapping is defined by the following conditions: the probability of given state of the coarse system is equal to that of all fine system states compatible with the respective coarse state, the dissipation per coarse grained object is similar in the two systems, constraints to the motion of a representative chain exist in the fine phase space, and the coarse phase space is adjusted such to represent them. Specifically, the chain inner blobs are constrained to move along the backbone of the coarse grained chain, while the end blobs move in the three-dimensional embedding space. The end blobs continuously redefine the diffusion path for the inner blobs. The input parameters governing the dynamics of the coarse grained system are calibrated based on the fine scale model behavior. Although the coarse model cannot reproduce the whole thermodynamics of the fine system, it ensures that the pair and end-to-end distribution functions, the rate of relaxation of segmental and end-to-end vectors, the Rouse modes, and the diffusion dynamics are properly represented.
提出了一种粗粒化方法，旨在再现线性单分散聚合物熔体中的链结构和动力学。参考体系是熔体的珠-簧型表示。粗粒化水平选择为等于缠结段中的珠子数Ne。粗模型仍然是离散的，并且包含每个代表精细尺度模型中Ne个连续珠子的团块。映射由以下条件定义：粗体系给定状态的概率等于与相应粗状态兼容的所有精细体系状态的概率，两个体系中每个粗粒化对象的耗散相似，精细相空间中存在对代表性链运动的约束，并且粗相空间经过调整以表示这些约束。具体而言，链内团块被约束沿着粗粒化链的主链移动，而末端团块在三维嵌入空间中移动。末端团块不断重新定义内团块的扩散路径。基于精细尺度模型行为校准控制粗粒化体系动力学的输入参数。虽然粗模型不能再现精细体系的整个热力学，但它确保了对分布函数和端到端分布函数、链段和端到端矢量的松弛速率、Rouse模式以及扩散动力学得到正确表示。
