Dispersion of nanosized aqueous suspensions of barium titanate with ammonium polyacrylate

The colloidal stability of nanosized barium titanate (BaTiO3) aqueous suspensions with ammonium polyacrylate (PAA-NH4) at different pH values has been investigated by means of zeta potential, adsorption isotherm, sedimentation, and rheology characterization. The isoelectric point of BaTiO3 powders is at pH 2.5 and the value of zeta potential is at its maximum near pH 10. The amount of leached barium ion decreases with increasing pH, but the change decreases with increasing initial pH. Adsorption of PAA-NH4 onto the surface of BaTiO3 decreases its zeta potential. Results show that PAA-NH4 adsorption follows Langmuir monolayer adsorption isotherms and the amount of PAA-NH4 required to stabilize nanosized BaTiO3 suspensions decreases as the pH increases. The mechanism of stabilization of BaTiO3 is shown to be electrosteric under the experimental conditions. Good agreement between zeta potential, sedimentation, and rheological tests is found, which identifies an optimum pH value of about 10 and an optimum dispersant concentration of about 2.0 wt%, independent of the solids volume fraction of suspensions.