Coadsorption of polylysine and the cationic surfactant cetyltrimethylammonium bromide on silica

Coadsorption of polymers and surfactants is a poorly understood process that occurs in a variety of complex fluid applications. In single-component solutions, the cationic polyelectrolyte polylysine and the cationic surfactant cetyltrimethylammonium bromide (CTAB) both adsorb to negatively charged silica surfaces. Here we use scanning angle reflectometry to contrast adsorption from single-component solutions with a sequential adsorption process and a coadsorption process. When adsorbed from single-component solutions, polylysine adsorbs irreversibly, whereas CTAB adsorption is reversible. In the sequential adsorption case, CTAB neither displaces nor adsorbs to preadsorbed polylysine layers. When solutions contain both CTAB and polylysine, they coadsorb to form mixed layers. Mixed layer formation is indicated by a dramatic alteration of the kinetics and reversibility of adsorption compared to either single-component case. The amounts of CTAB and polylysine adsorbed in the mixed layers are both similar to the amounts adsorbed from the respective single-component solution.