Light scattering of colloidal dispersions in non-polar solvents at finite concentrations. Silic spheres as model particles for hard-sphere interactions

Abstract

Static and dynamic light-scattering studies are reported for spherical model particles in non-polar solvents. The model particles have a core of silica and a dense surface layer of octadecylalcohol chains which makes them ‘oil soluble’. The refractive-index difference between particles and solvent is very small and so dispersions can be studied by means of light scattering up to high concentrations. Multiple-scattering effects are considered briefly. In cyclohexane the particles show repulsive forces which can be described by a hard-sphere interaction. The small refractive-index differences can also be used to detect differences in optical density in the silica core. The periphery of the core is found to be more dense than the centre. Furthermore, the small natural spread in refractive index of the particles can be used to differentiate between collective-diffusion and self-diffusion processes. Differences in refractive indexes can also be obtained by variations in the particle synthesis. In this way it is possible to study self-diffusion by following the motion of tracer particles.