Rheology of cohesive sediments

• Main Author: Partridge, Susan Jill
• Published: University of Bristol 1985
• Subjects: 530.41; Solid-state physics
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355635

Polystyrene latices of particle diameter 0.97 ~, 1.41 ~ and 1.92 ~, at an electrolyte concentration of 0.5 mol dm- 3 sodium chloride, were' sterically stabilised by the adsorption of a monolayer of a monodisperse nonionic surface active agent, C12E6• Optical microscopy showed that the resultant systems were weakly flocculated, with only slight agitation required to destroy the flocs. Calculations showed that the van der Waals attractive potential dominated the highly screened electrostatic repulsive potential; the particles were prevented from coagulating into the primary minimum through the presence of the steric barrier. Potential energy well depths of 7 - 15 kT were obtained. Rapid sedimentation of the systems occurred by consolidation of r..he aggregated structure after an induction period which increased with increasing volume fraction to give a final sediment volume fraction of approximately 0.4 - 0.45. Constant stress viscometry demonstrated that the suspensions were shear thinning with a limiting Newtonian viscosity at low stresses. At high stresses the viscosity was similar to that expected for a dispp.rsion of hard spheres as calculated from Krieger's equation~2 Shear wave propagation experiments were performed to measure the high frequency limit of the shear modulus as a function of volume fraction. The values obtained were compared with a theoretical model due to Zwanzig and Mountain79 and based on a statistical mechanical description of the microstructure combined with the pair interaction potential of the particles. Parameters required for the model were the suspension volume fraction, the Stern potential, the Hamaker constant and the extent of the adsorbed layer, all of which were determined independently of the rheological measurements. Good agreement was obtained between theoretical and experimental data when using a Barker Henderson perturbed hard sphere potential model to calculate the pair distributionfunction. The model thus provided a strong test of the use of liquid state theory for the prediction of the transport properties of colloidal suspensions. Predictions of the zero shear viscosity were made using a similar model.