Surfactant Microstructure and Particle Aggregation Control Using Amphiphile Adsorption on Surface-Functionalized Polystyrene Spheres

Abstract

Surfactant microstructure and particle aggregation control upon adding surface-functionalized 100 nm diameter polystyrene (PS) spheres to a cetyltrimethylammonium bromide (CTAB)/dodecylbenzenesulfonic acid (HDBS) mixed surfactant system has been studied using cryogenic transmission electron microscopy (cryo-TEM). The key premise is that selective adsorption of surfactant onto the spheres, driven primarily by charge interactions, impacts surfactant concentrations in the solutions, thus driving structures to different, concentration-dependent states. A concurrent effect is the role played by adsorption on the clustering of the PS spheres. The effects of adsorption are quite pronounced when aldehyde-functionalized PS spheres are added to a small cationic vesicle/micelle suspension: only large vesicles remain. On the other hand, an anionic vesicle suspension remains unperturbed by the addition of these PS spheres. The addition of PS spheres to a 1:1 CTAB/HDBS mass ratio solution results in huge PS clusters that precipitate from the suspension. These large clusters are networks of PS spheres connected by surfactant bilayers arising from hydrophobic interactions with neutrally charged vesicles or vesicle fragments. These results indicate that solid surface adsorption provides a viable way to modify microstructures in a mixed surfactant system, with additional effects resulting from the aggregation of the PS particles. These effects can potentially be useful when surfactant composition must be changed without additional surfactant consumption, for rheology modification, in templated material synthesis, as well as in understanding situations where surfactant could potentially be adsorbed by neighboring solid boundaries, such as surfactant-mediated oil recovery from porous rocks and detergency.