Surface chemistry-rheology inter-relationships in clay suspensions

Abstract

The relationship between electrolyte concentration and thixotropic behaviour in sodium-montmorillonite-based suspensions has been examined with a view to understanding the structural mechanisms that cause the observed thixotropy. Results presented indicate that the changes in the rheological behaviour of sodium-montmorillonite suspensions over the range of added NaCl concentrations can be adequately explained without resorting to the traditional edge-face, heterocoagulation model. The onset of thixotropy at low to moderate NaCl concentrations (0.05–0.1 M) can be explained by a combination of random coagulation and particle orientation effects. At higher NaCl concentrations (⩽0.2 M) face-face aggregation reduces the number of interacting flow units and both the overall rheological parameters and the degree of thixotropy decrease. Platelet interaction energy calculations utilising an average zeta potential based on treatment of the clay platelets as a homogenously charged platelet support the proposed mechanisms describing the changes in rheological behaviour.