Polymeric stabilisation of aqueous suspensions of barium titanate. Part I:Effect of pH

This article investigates the effect of the pH on the aqueous dispersion of barium titanate powders with anionic and cationic polyelectrolytes. The an ionic polymer tested was an ammonium salt of polyacrylic acid (PAA) with mo lecular weight (M-w) similar to 4000, and the cationic were two quaternary alkyl ammonium derived polymers, with M-w similar to 150,000 and similar to 7600. The anionic polyelectrolyte has been found to be very effective in t he alkalyne pH range, where the carboxylic groups are ionised. As result, t he suspension is electrostatically stabilised, and the yield stress values and viscosities are very low. The adsorption and effectiveness of this poly electrolyte could be reinforced by the presence of Ba2+ ions adsorbed on th e surface of the BaTiO3 particles. The cationic polyelectrolytes, on the co ntrary, are not effective stabilising the suspension: at alkaline pH, the l ong chain polymer has the tendency to bridge particles, and the short polym er does not generate zeta potential values high enough upon adsorption. At pH 4, their addition to the suspension is not of any advantage with respect to the suspension without polyelectrolytes. (C) 2000 Elsevier Science Ltd. All rights reserved.