Effect of formation of ion pairs on the stability of stoichiometric block ionomer complexes
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The dependences of the aggregation number and the size of micelles formed as a result of self-assembly in dilute solutions of block ionomers and oppositely charged polyelectrolytes on the degree of ionization of polyions, as well as on solvent quality and polarity, were theoretically analyzed. The micelle core is a polyelectrolyte complex and the corona is formed by hydrophilic nonionic blocks of the block ionomers. To describe the polyelectrolyte complex, a model that allows for the formation of ion pairs between oppositely charged groups on polymer chains was proposed. In terms of the Lifshitz approach to the description of polymer globules, the equilibrium concentration of the polymer in the complex and its surface tension as a function of the degree of ionization of polyelectrolyte chains and solvent polarity were found. It was shown that the proportion of ion pairs is small in a strongly polar complex and the polyelectrolyte complex is formed mainly as a result of attraction due to charge density correlation in the complex. As the solvent polarity increases, the proportion of ion pairs increases. In a solvent with low polarity, the formation of ion pairs that act as physical crosslinks between oppositely charged polyions is a driving force of complexation. With an increase in the number of ion pairs, the surface tension of polyelectrolyte complexes that form the micelle core of block ionomer complexes increases, thus leading to a considerable increase in the size of micelles.
KeywordsBlock Copolymer Polymer Science Series Diblock Copolymer Aggregation Number Polyelectrolyte Complex
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