Adsorption Phenomena at the Surface of Silica Spheres in a Binary Liquid Mixture

Silica spheres of 1600-\AA{} diameter immersed in the binary fluid water+2-6-lutidine have been studied by light-scattering techniques. The scattered light was seen to be strongly dependent on temperature and concentration. This effect is due to the appearance of a lutidine layer on the spheres. The layer thickness dramatically increases near a transition line were the spheres aggregate as a result of attractive interactions. This transition exhibits all the features predicted for the prewetting transition between high and low adsorption of a fluid on a surface.