Effect of aging time on the rheology of Laponite dispersions

The effect of aging time on aqueous Laponite dispersions containing sodium polyacrylate was analyzed by rheometric measurements. The rheological behavior of these dispersions was determined by oscillatory and flow experiments. Addition of sodium polyacrylate modifies the interactions between Laponite particles and, therefore, the physical state of the dispersion. The phase diagram of Laponite dispersions as a function of sodium polyacrylate concentration shows different sol–gel transitions for a specific Laponite concentration. The transition line goes to lower Laponite concentrations with aging time. A structural model permitted the characterization of the thixotropy of Laponite dispersions by means of the alignment of the internal structure to the applied shear rate and by the thixotropic times of the net breakdown and buildup processes. The thixotropy of dispersions in presence of sodium polyacrylate was less dependent on aging time, indicating that sodium polyacrylate reduces the aggregation rate of the formation of a three-dimensional network and permits better control of rheology, at least for 12 days after the preparation of dispersion.