Study of the Mechanism of Structure Formation in Aqueous Dispersions of Na+-Smectites

The paper presents the results of experimental studying colloidal structure and rheology of dilute aqueous Na+-montmorillonite dispersions by the capillary and rotational viscometry methods. Aqueous dispersions of clay particles undergo significant structural changes, which markedly affect the character of the flow of such systems. All these changes are managed by alterations in indifferent electrolyte concentration within a narrow concentration range. Certain critical concentration has been found to appear at a NaCl concentration of about 3 mM for the series of dispersions with solid contents of 0.25–3.0 wt %. This critical concentration is significantly lower than the coagulation thresholds reported in the experimental and theoretical works devoted to this scope. The substantial changes in the rheological behavior within this electrolyte concentration range may reflect both the processes of formation/disruption of aggregates and changes in the mechanism of either aggregation or structure formation. The obtained rheological data have been compared with theoretical calculations and the results of dispersion analysis (by the dynamic light scattering method) of aqueous dispersions. The data obtained widen the conceptions of the structuring processes in clay dispersions.