(85d) Effect of Thermal Treatment and Moisture On Silica Particle Charge in Non-Polar Solvents

Hydrophilic colloids such as silica do not readily acquire charge in non-polar solvents and have poor colloidal stability. Surfactants, such as Aerosol-OT (AOT), are known to impart charge on these hydrophilic particles in non-polar solvents, making them stable. However, the effect of surface chemistry and water content in such non-polar media is not well understood. In this study, we examine the effect of surface chemistry and moisture on the charge of silica particles in AOT-doped toluene. The surface chemistry of silica, specifically the density of silanol groups, is varied by thermal treatment of silica particles up to 1000^oC. In addition, the moisture content of the particle suspension is controlled by equilibrating them under different relative humidities. Changes in the surface chemistry as well as in moisture content significantly influence the charge of silica particles in AOT/toluene. We use Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and quartz crystal microblance (QCM) to gain insight into the effect of thermal treatment and moisture on the charging of silica particles. Furthermore, we relate these findings to the growth and composition of thin films formed via layer-by-layer (LbL) assembly of oppositely charged nanoparticles in non-polar solvents.