Adsorption of anionic surfactants on polystyrene latex surfaces

The adsorption of several anionic surfactants on polystyrene latexes of variable surface charge density was studied to provide a comprehensive understanding of the effects of surface charge density on surfactant adsorption. Adsorbed amounts were determined from direct analysis of the bulk surfactant concentration using ion chromatography. The data indicates that the relationship between adsorbed amount and surface charge density is more complex than previously believed.;The results suggest that as the surface charge density of the same sign as the adsorbing species increases, the adsorbed amount initially increases at very low surface potentials (0 to ;Analysis of two-component adsorption indicated that when anionic surfactants compete for an adsorbing surface, the adsorbed amount is greater than observed in the single component adsorption situations. This is true even for weakly adsorbed surfactants, and is presumably due to initially adsorbed surfactant causing enhanced chain-on-chain adsorption which results in higher adsorbed amounts. This effect is particularly evident for a two-tailed surfactant, since one of the hydrophobic tails may be free and available for adsorption while the other is attached to the surface. Displacement adsorption results displayed no significant change from the competitive adsorption cases because no displacement was occurring. This was found to be due to the enhanced chain-on-chain adsorption which resulted in increased adsorbed amounts identical to the coadsorption situation.