Abstract
By means of computer simulation and analytical theory, we first demonstrated that the interpolyelectrolyte complexes in dilute solution can spontaneously form hollow spherical particles with thin continuous shells (vesicles) or with porous shells (perforated vesicles) if the polyions forming the complex differ in their affinity for the solvent. The solvent was considered good for the nonionic groups of one macroion and its quality was varied for the nonionic groups of the other macroion. It was found that if the electrostatic interactions are weak compared to the attraction induced by the hydrophobicity of the monomer units, the complex in poor solvent tends to form “dense core–loose shell” structures of different shapes. The strong electrostatic interactions favor the formation of the layered, the hollow, and the filled structured morphologies with the strongly segregated macroions. Vesicles with perforated walls were distinguished as the intermediate between the vesicular and the structured solid morphologies. The order parameter based on the spherical harmonics expansion was introduced to calculate the pore distribution in the perforated vesicles depending on the solvent quality. The conditions of the core–shell and hollow vesicular-like morphologies formation were determined theoretically via the calculations of their free energy. The results of the simulation and theoretical approaches are in good agreement.
Highlights
Interpolyelectrolyte complexes (IPECs) are formed in solutions by oppositely charged polyions.IPECs play an important role in nature; for example, polyelectrolyte complexation occurs in chromatine fiber, formed by DNA and histones [1], and within cells in the interaction between DNA and enzyme proteins [2]
The formation of IPECs is driven by electrostatic interactions between the oppositely charged groups, as well as entropy change upon the release of counterions, which were bound to the free polyions [12,13,14,15]
The aim of the present study is to investigate the shape and distribution of monomer units in stoichiometric interpolyelectrolyte complexes consisting of two chains having different affinities for the solvent, depending on the length of the chains, solvent quality, and the Bjerrum length; namely, to obtain the conditions for the emergence of various morphologies, indicate the area of the hollow structures formation, and quantitatively describe the shapes of these hollow structures
Summary
Interpolyelectrolyte complexes (IPECs) are formed in solutions by oppositely charged polyions.IPECs play an important role in nature; for example, polyelectrolyte complexation occurs in chromatine fiber, formed by DNA and histones [1], and within cells in the interaction between DNA and enzyme proteins [2]. Interpolyelectrolyte complexes (IPECs) are formed in solutions by oppositely charged polyions. The formation of IPECs is driven by electrostatic interactions between the oppositely charged groups, as well as entropy change upon the release of counterions, which were bound to the free polyions [12,13,14,15]. If the charges of one sign prevail, the complexes are called nonstoichiometric They form micelles with the charged surface and are water-soluble due to the electrostatic interaction between water and charged monomer units. Solutions of oppositely charged polyelectrolytes, which carry an equal amount of positive and negative charges (stoichiometric case), have zero net charge and reveal macroscopic separation into polymer-rich and dilute phases [7,18,19,20,21]
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