Rapid electroacoustic method for monitoring dispersion: Zeta potential titration of alumina with ammonium poly(methacrylate)

The zeta potential (zeta) of 2-vol% and 10-vol% suspensions of a commercial alpha-alumina has been measured using the electroacoustic technique and found to be in good agreement with values reported previously from microelectrophoresis measurements. An increasingly negative zeta value was observed through semiautomatic addition of solutions of a ammonium salt of poly(methacrylic acid). The point of complete surface coverage was inferred from simultaneous conductivity measurements. The average particle size obtained from the electroacoustic dynamic mobility spectrum showed the effect of coagulation near the isoelectric point. The expected correlations among zeta, the viscosity, and the sedimentation volume were observed. The results illustrate the efficacy of the electroacoustic technique for examining colloidal dispersions.