Chain conformations and phase separation in polymer solutions with varying solvent quality
Chain conformations and phase separation in polymer solutions with varying solvent quality
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DOI：
10.1002/pol.20210526
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发表时间：
2021-10-02
影响因子：
3.4
通讯作者：
Cheng, Shengfeng
中科院分区：
文献类型：
--
作者：
Huang, Yisheng;Cheng, Shengfeng
分子动力学模拟用于研究以 Lennard-Jones 液体为溶剂的溶液中，当聚合物和溶剂之间的相互作用强度变化时，以 Kremer-Grest 珠弹簧模型为代表的单聚合物链的构象。结果表明，当聚合物-溶剂相互作用不利时，链会像在不良溶剂中所预期的那样崩溃。为了获得更有吸引力的聚合物-溶剂相互作用，溶剂质量得到改善，链逐渐被溶剂化，并表现出理想的然后膨胀的构象。然而，当聚合物-溶剂相互作用强度进一步增加至超过聚合物-聚合物和溶剂-溶剂相互作用强度的约两倍时，链表现出意想不到的塌缩行为。相应地，对于强聚合物-溶剂吸引力，在多链溶液中观察到相分离。这些结果表明，在非常有吸引力的聚合物-溶剂相互作用下，溶剂再次变得有效。尽管如此，在此极限下链崩解和相分离的机制不同于由不利的聚合物-溶剂相互作用导致的不良溶剂的情况。在后者中，溶剂被排除在塌缩链的域之外，而在前者中，溶剂仍然存在于塌缩链的弥漫体积中或与纯溶剂相分离的富含聚合物的域中。在强聚合物溶剂吸引力的限制下，溶剂充当将单体粘在一起的胶水，导致单链塌陷和多链聚集和相分离。
Molecular dynamics simulations are used to investigate the conformations of a single polymer chain, represented by the Kremer-Grest bead-spring model, in a solution with a Lennard-Jones liquid as the solvent when the interaction strength between the polymer and solvent is varied. Results show that when the polymer-solvent interaction is unfavorable, the chain collapses as one would expect in a poor solvent. For more attractive polymer-solvent interactions, the solvent quality improves and the chain is increasingly solvated and exhibits ideal and then swollen conformations. However, as the polymer-solvent interaction strength is increased further to be more than about twice the strength of the polymer-polymer and solvent-solvent interactions, the chain exhibits an unexpected collapsing behavior. Correspondingly, for strong polymer-solvent attractions, phase separation is observed in the solutions of multiple chains. These results indicate that the solvent becomes effectively poor again at very attractive polymer-solvent interactions. Nonetheless, the mechanism of chain collapsing and phase separation in this limit differs from the case with a poor solvent rendered by unfavorable polymer-solvent interactions. In the latter, the solvent is excluded from the domain of the collapsed chains while in the former, the solvent is still present in the pervaded volume of a collapsed chain or in the polymer-rich domain that phase separates from the pure solvent. In the limit of strong polymer-solvent attractions, the solvent behaves as a glue to stick monomers together, causing a single chain to collapse and multiple chains to aggregate and phase separate.