Adhesion and Wear of Colloidal Silica Probed by Force Microscopy

The adhesion and wear of colloidal silica nanoparticles (50 nm diameter) dispersed in a film have been directly studied using atomic force microscopy (AFM) under aqueous solution conditions. The surface adhesion is found to peak in strength between pH 4-5. Using the JKR contact mechanics model, the energy for a single Si-OH/Si-OH interaction was estimated to be ~0.4 kcal/mol. Tribochemical wear of the silica particles, and their displacement from the film, is enhanced at high pH due to the increased facility of silica dissolution and the concomitant increase in attendant inter-particle repulsion.