Modeling of charged amphiphilic copolymer stars near hydrophobic surfaces

Numerical self-consistent field theory has been applied to amphiphilic copolyelectrolyte stars in the solution and at interfaces both in one- and two-gradient coordinate systems. Our focus is on polymer stars for which the solvent is poor for the short blocks in the center and good for the longer charged chain parts at the periphery of the star. Both in solution as well as near an interface, the structure of the core is influenced by the hydrophobic interactions that tend to form a compact globule with size Rc and the forces exerted by the charged peripheral chain parts that like to expand the core. When the distance H of the center of the star to the surface becomes smaller than the total size R, the interaction force becomes significant; it is positive for Rc <H <R, and rather suddenly becomes strongly attractive at shorter distances when the core can adsorb. Hence, the adsorption as well as the desorption of stars involves the passing of an activation barrier. Details of this barrier are important for a rational design of polymer stars that are of use to modify surface properties