Transfer Matrix Model of pH Effects in Polymeric Complex Coacervation
Transfer Matrix Model of pH Effects in Polymeric Complex Coacervation
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DOI：
10.1021/acs.jpcb.1c03065
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发表时间：
2021-07-30
影响因子：
3.3
通讯作者：
Sing, Charles E.
中科院分区：
文献类型：
--
作者：
Knoerdel, Ashley R.;McTigue, Whitney C. Blocher;Sing, Charles E.
带相反电荷的聚电解质可以发生缔合相分离，这一过程称为聚合物复合物凝聚。这种现象是由聚阴离子和聚阳离子之间的静电引力驱动的，导致形成聚合物致密凝聚相和共存的聚合物稀释上清相。最近人们对凝聚的物理起源和特征产生了极大的兴趣。但值得注意的是，实验经常使用弱聚电解质，其电荷状态取决于溶液 pH 值，而理论或计算工作通常假设强聚电解质保持完全充电。为了解决这一限制，人们只做出了一些努力，因此很少有人探索 pH 值如何影响复杂的凝聚。在本文中，我们修改了凝聚的转移矩阵理论来解释酸碱平衡，利用其直接解释一些会影响单体充电的局部离子相关性的能力。我们表明，凝聚可以通过带相反电荷的单体的接近来稳定弱聚电解质的带电状态，并且可以导致不对称相图，其中带正电和带负电的聚电解质在任一链的 pK(a) 附近表现出不同的行为。具体而言，当一种聚电解质仅部分带电时，一种盐类被分配到凝聚层以维持电中性。这导致上清液中相同盐类的消耗，并且总体上可以抑制相分离。我们还证明，当其中一种物质仅部分带电时，体积分数非化学计量但电荷化学计量的混合物表现出形成凝聚相的最大倾向。
Oppositely charged polyelectrolytes can undergo an associative phase separation, in a process known as polymeric complex coacervation. This phenomenon is driven by the electrostatic attraction between polyanion and polycation species, leading to the formation of a polymer-dense coacervate phase and a coexisting polymer-dilute supernatant phase. There has been significant recent interest in the physical origin and features of coacervation; yet notably, experiments often use weak polyelectrolytes the charge state of which depends on solution pH, while theoretical or computational efforts typically assume strong polyelectrolytes that remain fully charged. There have been only a few efforts to address this limitation, and thus there has been little exploration of how pH can affect complex coacervation. In this paper, we modify a transfer matrix theory of coacervation to account for acid-base equilibria, taking advantage of its ability to directly account for some local ion correlations that will affect monomer charging. We show that coacervation can stabilize the charged state of a weak polyelectrolyte via the proximity of oppositely charged monomers, and can lead to asymmetric phase diagrams where the positively and negatively charged polyelectrolytes exhibit different behaviors near the pK(a) of either chain. Specifically, there is a partitioning of one of the salt species to a coacervate to maintain electroneutrality when one of the polyelectrolytes is only partially charged. This results in the depletion of the same salt species in the supernatant, and overall can suppress phase separation. We also demonstrate that, when one of the species is only partially charged, mixtures that are off-stoichiometric in volume fraction but stoichiometric in charge exhibit the greatest propensity to form coacervate phases.