Krakoviack V, Hansen J-P, Louis A A
Department of Chemistry, University of Cambridge, Lensfield Road, United Kingdom.
Phys Rev E Stat Nonlin Soft Matter Phys. 2003 Apr;67(4 Pt 1):041801. doi: 10.1103/PhysRevE.67.041801. Epub 2003 Apr 25.
Solutions of interacting linear polymers are mapped onto a system of "soft" spherical particles interacting via an effective pair potential. This coarse-graining reduces the individual monomer-level description to a problem involving only the center of mass (c.m.) of the polymer coils. The effective pair potentials are derived by inverting the c.m. pair distribution function, generated in Monte Carlo simulations, using the hypernetted chain closure. The method, previously devised for the self-avoiding walk model of polymers in good solvent, is extended to the case of polymers in solvents of variable quality by adding a finite nearest-neighbor monomer-monomer attraction to the previous model and varying the temperature. The resulting effective pair potential is found to depend strongly on temperature and polymer concentration. At low concentration the effective interaction becomes increasingly attractive as the temperature decreases, eventually violating thermodynamic stability criteria. However, as polymer concentration is increased at fixed temperature, the effective interaction reverts to mostly repulsive behavior. These issues help to illustrate some fundamental difficulties encountered when coarse-graining complex systems via effective pair potentials.
相互作用的线性聚合物溶液被映射到一个通过有效对势相互作用的“软”球形粒子系统。这种粗粒化将单个单体水平的描述简化为一个仅涉及聚合物链质心（c.m.）的问题。有效对势是通过使用超网链闭合反转在蒙特卡罗模拟中生成的质心对分布函数来推导的。该方法先前是为良溶剂中聚合物的自回避行走模型设计的，通过在先前模型中添加有限的最近邻单体 - 单体吸引力并改变温度，扩展到了不同质量溶剂中聚合物的情况。发现所得的有效对势强烈依赖于温度和聚合物浓度。在低浓度下，随着温度降低，有效相互作用变得越来越有吸引力，最终违反热力学稳定性标准。然而，在固定温度下增加聚合物浓度时，有效相互作用大多恢复为排斥行为。这些问题有助于说明通过有效对势对复杂系统进行粗粒化时遇到的一些基本困难。
