Selective co-deposition of anionic silica particles at hydrophobic surfaces from formulations of oppositely charged polymers and surfactants

Abstract

The surface-selective surface deposition of anionic hydrophilic silica particles from aqueous polymer–surfactant formulations was investigated by in-situ null-ellipsometry. The formulations, with or without silica particles, contained anionic sodium dodecylsulfate (SDS) and a cationic polymer, cationic hydroxyethyl cellulose (cat-HEC) or a copolymer of acrylamide and methacrylamidopropyl trimethylammonium chloride (AAm/MAPTAC). Surface deposition from the formulations onto model surfaces of either anionic hydrophilic, or hydrophobized, silica was induced by controlled dilution of the formulations into the coacervation region, and was monitored with time by ellipsometry. The dilution simulated a rinsing process in a typical application. In all cases a steady-state surface layer remained after extensive dilution. An enhanced deposition from the silica-containing formulations was found on the hydrophobized silica surface, indicating a substantial co-deposition of silica particles. Much less co-deposition, or none at all, was found on hydrophilic silica. The opposite trend, enhanced co-deposition on hydrophilic silica, was previously found in similar experiments with hydrophobic silicone oil droplets as co-deposants (Clauzel et al., 2011). The amphiphilic cationic polymers evidently favor a “mismatched” co-deposition of anionic particles to hydrophobic surfaces, or vice versa. The findings suggest a strategy for surface-specific delivery of particles to surfaces.