Analysis of Partitioning of Salt through Doping of Polyelectrolyte Complex Coacervates
Analysis of Partitioning of Salt through Doping of Polyelectrolyte Complex Coacervates
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DOI：
10.1021/acs.macromol.0c00797
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发表时间：
2020-08-25
期刊：
影响因子：
5.5
通讯作者：
Larson, Ronald G.
中科院分区：
文献类型：
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作者：
Ghasemi, Mohsen;Friedowitz, Sean;Larson, Ronald G.
盐离子在化学计量比聚电解质复合凝聚体(PECs)中的掺杂被模拟为一个理论，该理论包括作为平衡反应的聚合物离子配对和反离子吸附，以及捕捉聚电解质电荷连接性影响的Flory-Huggins自由能和静电关联。该模型表明，在低盐浓度下，PEC中的盐含量与(外部)上清液中的盐浓度成线性关系，这与Schlenoff小组的实验观测结果一致。我们发现，只有在强盐离子吸附的极限下，PEC中的所有盐离子都与聚电解质结合；对于每个离子的结合自由能高达几个k(B)T，即使在最低的盐浓度下，PEC中的相当一部分盐离子也是自由的(或未结合的)。当上清液中的盐浓度增加到超过这一线性区域的较高值时，PEC与水和游离盐离子强烈膨胀，与实验观察到的类似。该模型还预测了盐离子在PEC中的分配行为主要受离子专一性的影响，表现为盐离子吸附和聚电解质离子配对的强度，这与Schlenoff和他的同事的观察结果一致。在适当选择参数的情况下，理论与文献中的实验掺杂和相行为数据符合得很好。
Doping of salt ions within stoichiometric poly-electrolyte complex coacervates (PECs) is modeled with a theory that includes polymer ion pairing and counterion adsorption as equilibrium reactions along with Flory-Huggins free energy and electrostatic correlations that capture the effects of polyelectrolyte charge connectivity. The model shows at low salt concentration a region in which the salt content in the PEC depends linearly on the salt concentration in the (external) supernatant, consistent with the experimental observations of the Schlenoff group. We find that only in the limit of strong salt ion adsorption are all salt ions in the PEC bound to polyelectrolytes; for binding free energies up to several k(B)T per ion, a significant fraction of the salt ions in the PEC are free (or unbound), even at the lowest salt concentration. When the salt concentration in the supernatant is increased to higher values beyond this linear regime, the PEC strongly swells with water and free salt ions, similar to that observed experimentally. The model also predicts that the partitioning behavior of salt ions into the PEC is primarily governed by ion-specific effects, which manifest themselves in the strength of salt ion adsorption and polyelectrolyte ion-pairing, in agreement with observations of Schlenoff and co-workers. With an appropriate choice of parameters, the theory provides good agreement with experimental doping and phase behavior data in the literature.