Interaction forces between silica surfaces in cationic surfactant solutions: an atomic force microscopy study

The interaction forces between silicon oxide surfaces in the presence of surfactant solutions were studied. Based on the qualitative and quantitative analysis of these interaction forces the correlation with the structure of the aggregates on the surfaces is analyzed. A colloidal probe atomic force microscope (AFM) was used to measure the forces between two colloidal silica particles and between a colloidal particle and a silicon wafer in the presence of hexadecyltrimethylammonium bromide (CTAB) at concentrations between 0.005 mM and 1.2 mM. Different interaction forces were obtained for the silica particle-silica particle system when compared to those for the silica particle-silicon wafer system for the same studied concentration. This indicates that the silica particles and the silicon wafer have different aggregate morphologies on their surfaces. The point of zero charge (pzc) was obtained at 0.05 mM CTAB concentration for the silica particles and at 0.3mM for the silica particle-silicon wafer system. This indicates a higher charge at the silicon wafer than at the silica particles. The observed long range attractions are explained by nanobubbles present at the silicon oxide surfaces and/or by attractive electrostatic interactions between the surfaces, induced by oppositely charged patches at the opposing Si oxide surfaces.