Rheology of Laponite colloidal dispersions modified by sodium polyacrylates

The rheological properties of Laponite dispersions were studied in aqueous systems containing an anionic polyelectrolyte. Sodium polyacrylate of 2000 g/mol molecular weight was used as polyelectrolyte. The effect of three variables on lineal viscoelasticity was studied. The variables are Laponite concentration, ionic strength and sodium polyacrylate concentration. All experiments were carried out at constant pH, and the rheology was analysed 6 days after its preparation. The rheological behavior of these dispersions can characterise the physical state of dispersion. Addition of sodium polyacrylate modifies the interactions between particles and the physical state of the dispersion can be changed. In order to determine the physical state, the phase diagram of Laponite dispersions was completed as a function of sodium polyacrylate concentration. The phase diagram shows different sol–gel transitions depending on ionic strength. At constant Laponite concentration and ionic strength, two transition lines were found by varying the sodium polyacrylate concentration.