Adsorption of Anionic and Cationic Surfactants on Anionic Colloids: Supercharging and Destabilization

We present herein a study on the adsorption of anionic (SDS), cationic (CTAB), and nonionic (C12E5) surfactants onto anionic silica nanoparticles. The effects of this adsorption are studied by means of the static structure factor, S(q), and the collective diffusion coefficient, D-c, obtained from small-angle X-ray scattering and dynamic light scattering measurements, respectively. The effective charge on the particles was determined also from classical electrophoresis and electroacoustic sonic-amplitude measurements. The surface tension of the sample was also investigated. Of particular note is the adsorption of SDS onto the silica nanoparticles, which leads to supercharging of the interface. This has interesting repercussions for structures obtained by the layer-by-layer (LbL) technique, because emulsions stabilized with supercharged and hydrophobized silica are perfect candidates for use in a multilayer system.