A study of silica nanoparticle adsorption using optical reflectometry and streaming potential techniques

The kinetics of adsorption of monodisperse nanosized silica particles (32-1 90 nm diameter) on silicon wafers modified with an aminopropylsilane have b een studied by optical reflectometry under stagnant-flow conditions. The ad sorption of negatively charged particles on a positively charged wafer surf ace is driven by electrical double layer attraction and was not found to be measurably reversible. The initial rate of particle adsorption decreases w ith increasing particle size while the equilibrium amount adsorbed increase s with electrolyte concentration. The effect of particle adsorption on the zeta potential of similarly modified glass slides was measured using stream ing potential apparatus. The coverage of particles was varied using electro lyte as indicated by the reflectometry measurements. The results suggest th at displacement of the plane of shear is not localized to particle covered areas.