THE PRODUCTION OF THIXOTROPIC SUSPENSIONS BY CONTROL OF DISPERSANT CONCENTRATION

The effect of dispersant concentration on the rheological behavior of suspensions of sub-micron aluminum oxide particles in either water or dodecane was studied using a double concentric cylinder rheometer. In the electrosterically stabilized aqueous system, the suspensions under went a sharp transition from coagulated to dispersed as the concentrat ion of the dispersant, ammonium poly(methacrylate), was increased. In the sterically stabilized dodecane system, as the concentration of the dispersant, 12-hydroxy stearic acid ester, was increased, the initial ly coagulated suspensions became highly thixotropic at concentrations less than that needed for stability. The difference in behavior betwee n these two systems is caused by the way that the interparticle forces are affected by the concentration of dispersant for the two types of stabilization mechanisms. The technique of inducing thixotropy by cont rol of the dispersant concentration has certain advantages including w ide applicability and not requiring special additives.