Time Dependence of Silica Surfaces on Their Interactions in Water and Alkaline Solutions

Spherical silica particles are widely used to study the stability of colloids. This is because the stability of silica particles is important in industrial processes and also because monodispersed particles are available in various sizes, allowing fundamental investigations on colloidal stability to be performed. However, it is often assumed that the surface properties of silica do not change during the measurements, e.g. for 60 min. In the present study, we used the atomic force microscope to determine the validity of this assumption by studying the change in the surface microstructure of silica with its immersion time in water and alkaline solutions. The microstructure of silica surfaces was found to change with the immersion time, even in water. This change was especially large for solutions of high pH. These changes are explained in terms of the hydrogen bonds between the silanol groups protruding from the silica surfaces, whose length depends on the solution pH and the immersion time.