Hydrophobic-Charged Block Copolymer Micelles Induced by Oppositely Charged Surfaces: Salt and pH Dependence

Abstract

We analyze the possibility of inducing surface micellization of hydrophobic and charged block copolymers by an oppositely charged surface using a two-state model with lateral correlations among adsorbed chains. The electrostatic attraction between the charged block and the charged surface induces diblock copolymer micellization on the surface at copolymer concentrations well below the critical micelle concentration in the bulk. We study systems with strong charge groups which have fixed charge densities and systems with weak charge groups which have solution-dependent degrees of ionizations. We analyze the effects of salt concentration, solution pH, surface charge density, polyelectrolyte block line charge density, surface tension of the hydrophobic block, and polymerization degrees of the blocks on the induced micellization. It is found that at low salt concentrations the number of chains per micelle does not significantly depend on the degree of polymerization of the charged block. The addition of salt increases the critical surface micelle concentration when the electrostatic attraction between the charged blocks and the surface dominates the electrostatic repulsion among adsorbed chains. At low salt concentration, the excluded volume has a minor effect on surface induced micelles for systems with strong charge groups. However, in systems with weak charge groups, where both the surface and block degrees of ionizations are determined self-consistently as a function of pH, the excluded volume decreases the pH effect on the polyelectrolyte degree of ionization at surfaces.