The elasticity of weakly flocculated suspensions

Abstract

Monodisperse polystyrene lattices, at high electrolyte concentrations and with an adsorbed layer of nonionic surface active agent, produced weakly flocculated dispersions which sedimented rapidly to give a final sediment concentration of ∼30% by volume. Three lattices were used with particle sizes in the range 1–2 μm. The surface active agent used was C12E6. Optical microscopy of dilute systems showed that dense flocs were formed which were easily disrupted by small shear stresses. Shear wave propagation experiments were used to give the volume fraction dependence of the wave rigidity modulus, G̃, of these systems at high frequency. The high frequency limit to the shear modulus, G(∞), was calculated from the particle pair potential and the particle pair distribution function determined by using one of the current perturbation theories. The interparticle pair potential was calculated from a combination of van der Waals’ attraction, and both steric and electrostatic repulsion. Good agreement was obtained between the value of G(∞) obtained from this statistical mechanical analysis and the experimental value of G̃ over the full range of volume fraction studied.