Department of Physics, Ningbo University, Ningbo, Zhejiang, 315211, China.
Soft Matter. 2019 Mar 20;15(12):2560-2570. doi: 10.1039/c8sm02131g.
Langevin dynamics (LD) simulations have been performed to study the conformations and stratification of grafted three-arm polyelectrolyte (PE) stars in response to external electric fields. The grafted chains with neutral stems and fully charged branches were immersed in a salt-free solution sandwiched between the grafting electrode and a second oppositely charged electrode. The branching points of neutral-stem PE brushes at low grafting densities exhibit a bimodal distribution normal to the grafting electrode. With increasing grafting density, the molecular conformations in the brush layer become more complex with the emergence of multi-mode distributions of the branching point monomers. Under strong electric fields, the fraction of grafted chains with either nearly completely stretched stems or collapsed branches onto the grafting electrode gradually decreases with increasing grafting density due to the stronger electrostatic screening from counterions and monomer charges at higher grafting densities. Simulation results revealed that a collapsing electric field promotes the stratification within the brush layer, leading to high degrees of charge overcompensation from charged monomers collapsed onto the oppositely charged grafting electrode. An approximate analytical self-consistent field model was developed to examine the stratification within the brush layer. Regarding the fraction of grafted chains with the free branches in the upper layer, the prediction of the analytical model qualitatively agrees with the simulation results.
朗之万动力学（LD）模拟已被用于研究接枝三臂聚电解质（PE）星在外部电场作用下的构象和分层。中性支链和全带电支链的接枝链被浸入在接枝电极和第二对带相反电荷的电极之间的无盐溶液中。在低接枝密度下，中性支链 PE 刷的支化点沿垂直于接枝电极的方向呈双峰分布。随着接枝密度的增加，刷层中的分子构象变得更加复杂，支化点单体的多模态分布出现。在强电场下，由于更高接枝密度下的反离子和单体电荷的更强静电屏蔽作用，具有几乎完全伸展的支链或坍塌支链的接枝链的分数逐渐降低。模拟结果表明，坍塌电场促进了刷层内的分层，导致带电荷的单体坍塌到带相反电荷的接枝电极上，从而实现了高电荷过度补偿。开发了一个近似的解析自洽场模型来研究刷层内的分层。对于上层中带有自由支链的接枝链分数，解析模型的预测定性上与模拟结果一致。
