Contrast variation in light scattering: Silica spheres dispersed in apolar solvent mixtures

Abstract

The contrast variation method, well known from small-angle neutron and X-ray experiments, is applied to a light-scattering study of colloidal dispersions of spherical particles. The theory is rederived in terms of light-scattering parameters and extended to cases of preferential adsorption of one of the solvent components at the particle surface. Experiments were carried out with spherical monodisperse lyophilic silica dispersions in (binary) mixtures of cyclohexane and transdecaline. It is found that the silica particles have a low mean refractive index and that significant optical density variations occur in the particle. Cyclohexane is preferentially adsorbed. For the system under consideration the light-scattering contrast variation method appears to be a valuable technique for particle characterization.