链段刚性对非溶剂致相分离成膜过程影响的耗散粒子动力学模拟

通过分子动力学(MD)模拟映射方法构建了符合聚醚砜(PES)刚性结构的耗散粒子动力学(DPD)简谐力场, 并研究了PES链段刚性对PES/N-甲基-2-吡咯烷酮(NMP)/水体系非溶剂致相分离(NIPS)过程的影响. 结果表明, 由于非溶剂和溶剂在两相界面上发生的质量交换, 导致在相界面处PES链段发生堆积, 形成了薄而致密的聚合物表层, 在PES溶液内部, 由于非溶剂的侵入导致体系发生了旋节相分离, 从而在整体上得到了明显的非对称结构; 同时, PES链段刚性的提升能够明显加快体系的相分离速度, 导致相界面处的PES薄层形成得更加快速, 薄层更加致密、 孔径更小, 而对内部的疏松结构影响较小; 此外, 结合不同力场下聚合物浓度对相分离过程的影响可以发现, 不同PES浓度下, 链段刚性的提升对相分离过程的特征和演变趋势没有造成根本性的影响, 与经典的弹簧力场的模拟结果在整体趋势上有相似性. 研究结果表明, 简谐力场能提升PES链段的刚性, 从而能更真实地模拟实际体系的非溶剂相分离法成膜过程.

Dissipative Particle Dynamics Simulation of the Effect of Polymer Chain Rigidity on Membranes Formation by Nonsolvent Induced Phase Separation Process

In this work， a new harmonic force field that was consistent with polyethersulfone（PES） structure was constructed by a mapping between the molecular dynamics（MD） simulation and the dissipative particle dynamics（DPD）， and the effect of polymer chain rigidity on the formation of PES membranes via the nonsolvent induced phase separation（NIPS） process with N-methyl-2-pyrrolidone（NMP） as the solvent and H₂O as the nonsolvent coagulant was investigated. The results showed that the rapid exchange of the solvent and nonsolvent at the interface between NMP/PES solution and H₂O caused the accumulation of PES at the interface， resulting in the formation of a thin but dense polymer layer near the interface. And in the interior region of the PES solution， the addition of the nonsolvent induced a spinodal decomposition of the PES solution， thus presenting asymmetric morphologies with a dense layer on the top surface and a porous sub-layer beneath the top surface. Also， the enhancement of PES chain rigidity can significantly improve the phase separation speed of the system and lead to the formation of the surface layer with a smaller pore size more quickly. Moreover， the effect of PES chain rigidity on membrane structure is obviously on the surface layer rather than the sub-layer. In addition， by comparing the influence of polymer concentration on the NIPS process in different force fields， it can be found that the enhancement of PES chain rigidity with different PES concentrations did not cause fundamental changes in the characteristics and evolution trend of the phase separation process. And the effect of the harmonic force field and classical spring force field on the NIPS process is similar. The simulation results reveal that the harmonic force field constructed in this study can obviously improve the rigidity of the PES chain， and thus can be helpful to simulate the membrane formation process of phase separation more realistically.