Polyelectrolytes and Oppositely Charged Surfactants in Organic Solvents: From Reversed Micelles to Soluble Polymer-Surfactant Complexes

Abstract

This work studies aggregates formed by poly(N-ethyl-4-vinylpyridinium bromide) (PEVP) and oppositely charged sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol OT) molecules in aliphatic hydrocarbon solvents (octane and hexane). It demonstrates that various polycation-surfactant structures are formed during PEVP solubilization in Aerosol OT solutions depending on the amount of water added to the system. At high degrees of hydration PVPE incorporates in the water pool of a reversed micelle formed by the surfactant where the polycation chain is substantially condensed. According to the light scattering and ultracentrifugation data, the incorporation of the polycation affects little the size of the reversed micelles. Under these conditions the water pools of PEVP-containing micelles may also incorporate other macromolecules (e.g., bovine serum albumin) simultaneously with the polycation. At the critical degree of hydration PEVP represents a swollen globule compressed by the micellar matrix. The density of the polycation in such globules equals about 0.5 g/cm 3 and about 50% of the globule volume is occupied by water molecules. Below the critical degree of hydration the polycation and the surfactant form a stoichiometric polymer-surfactant complex soluble in aliphatic hydrocarbons. The dimensions of such complexes are significantly higher than those of the initial empty reversed micelles, and they apparently represent «comblike» structures in which the Aerosol OT head groups are electrostatically bound with the charged units of PEVP, whereas the hydrophobic tails of the surfactant, «grafted» to the polycation, are exposed to the bulk solvent