Salt Resistance as a Measure of the Strength of Polyelectrolyte Complexation
Salt Resistance as a Measure of the Strength of Polyelectrolyte Complexation
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DOI：
10.1021/acs.macromol.1c02151
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发表时间：
2022-02-08
期刊：
影响因子：
5.5
通讯作者：
Schlenoff, Joseph B.
中科院分区：
文献类型：
--
作者：
Digby, Zachary A.;Yang, Mo;Schlenoff, Joseph B.
当混合时，正聚电解质和负聚电解质的溶液可以自发地相分离成共混的水合复合物或凝聚物（佩奇）。在佩奇内带相反电荷的聚电解质之间的电荷配对相互作用随着盐MA的加入而减弱。在足够高浓度的MA下，PEC可以解离回到单独的聚电解质中，从而逆转由电荷配对和其他相互作用引起的液-液相分离。该临界盐浓度（CSC）或“耐盐性”已被广泛用于比较佩奇中缔合的稳定性和强度。然而，CSC并不总是观察到的，它显示出很强的依赖于包含MA的离子的类型。此外，CSC更可能在由聚羧酸酯组装的佩奇（一种弱聚羧酸酯）中观察到。在这里，它表明，缺乏实验CSC与离子M+和A（-）在PEC中的优选作用，反离子对共离子，或特定离子对特定的反离子重复单元的特异性相关，通过量热测量揭示。定量地证明了弱聚电解质的电离焓在提供实验可测量的CSC中的重要性。
When mixed, solutions of positive and negative polyelectrolytes may spontaneously phase-separate into blended, hydrated complexes or coacervates (PECs). Charge-pairing interactions between oppositely-charged polyelectrolytes within PECs are weakened with the addition of salt MA. With a sufficiently high concentration of MA, the PEC may dissociate back into the individual polyelectrolytes, reversing the liquid-liquid phase separation induced by charge pairing and other interactions. This critical salt concentration (CSC), or "salt resistance," has been extensively used to compare the stability and strength of association in PECs. However, the CSC is not always observed, and it shows a strong dependence on the type of ions comprising MA. In addition, the CSC is more likely to be observed with PECs assembled from polycarboxylates, a type of weak polyelectrolyte. Here, it is shown that a lack of experimental CSC is correlated with the preferred role of ions M+ and A(-) in the PEC, counterion versus co-ion, or the specificity of a particular ion for a particular polyelectrolyte repeat unit, revealed by calorimetric measurements. The importance of the enthalpy of ionization of weak polyelectrolytes in providing an experimentally measurable CSC is quantitatively demonstrated.