Characterization of Colloidal Silica and Its Adsorption Phenomenon with Silicon-Base Surfactants with Relation to Film Strength

The strength of coated film containing silica can be attributed to the packing density of the silica particles and the extent of siloxane bond formation between them. The adsorption of a silicon-base surfactant on silica surfaces hinders such bond formation. Such adsorption occurs through hydrogen bonding between the free silanol on the silica surface and the oxygen of the PEO of a surfactant chain. Variation in surface properties of silica affects the formation of these hydrogen bonds. Colloidal silica particles show a large variation in surface characteristics, such as the aluminum content on the surface of the particles. These properties determine the surface charge of the silica particles, which is apparent from the variation in zeta potential and the amount of acid consumption prior to an inflection point being reached in titration curves. The concentration of acid required to reach the inflection point is higher for silica with higher Al(OH)4−content. Higher levels of Al(OH)4−cause less adsorption of the surfactant by preventing hydrogen bonding of silanol to PEO of the surfactant. Higher levels of surfactant adsorbed on silica lower the strength of the film due to the reduction of the extent of the siloxane bond formed between two silicon atoms.