Surface Deposition and Phase Behavior of Oppositely Charged Polyion−Surfactant Ion Complexes. 2. A Means to Deliver Silicone Oil to Hydrophilic Surfaces

The delivery of emulsified silicone oil to hydrophilic silica surfaces by mixtures of cationic polysaccharides and SDS has been studied by in situ null ellipsometry, dynamic light scattering, and turbidity measurements. The emulsion contained silicone oil droplets with a hydrodynamic radius of 18 nm, stabilized by anionic and nonionic surfactants. The investigated polysaccharides were cat-guar and cat-HEC. Both polyions have qualitatively similar adsorption and bulk properties in mixtures with surfactant and emulsion droplets, and both are able to deliver emulsion droplets to the hydrophilic silica surface under suitable conditions. However, there are important quantitative differences that are attributed to a more hydrophobic character of cat-HEC than of cat-guar. The differences in hydrophobicity affect the adsorption from polyelectrolyte/emulsion/surfactant mixtures to hydrophilic silica, especially when an initially surfactant-rich mixture is brought toward phase separation by dilution. Under these conditions, adsorption is obtained only for mixtures with cat-guar. Dynamic light scattering performed on the bulk solutions reveals different aggregation behavior of the cat-guar and the cat-HEC with the silicone oil droplets in the studied surfactant concentration range and the results agree with findings from the adsorption study. Adsorption during dilution of a polyelectrolyte−surfactant mixed solution in the presence of silicone oil droplets gives a larger adsorbed amount and a thicker layer compared to the polyelectrolyte−surfactant mixture without emulsion.