Gravitational compression in colloidal suspension

Abstract

Gravitational effect in colloidal suspensions is examined both theoretically and experimentally by light scattering. In contrast to the previous theory the present theory predicts the cube of the nearest-neighbour distance to vary linearly as a function of height of the suspension. The position of the first peak in the static structure factor of the suspension having liquid-like order is used to obtain average nearest-neighbour distance. The experimental data fit well to the present theory. The bulk modulus of the liquid order estimated for the first time by this method is found to evolve as a function of time. The time taken for the colloidal suspension to reach gravitational equilibrium as well as deionisation equilibrium is obtained. The time to reach gravitational equilibrium is found to be much less than earlier theoretical estimates based on a simple model. A possible mechanism for this is proposed. Concentration dependence of the saturation bulk modulus is obtained and discussed.