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 anionic polymer tested was an ammonium salt of polyacrylic acid (PAA) with molecular weight (Mw) ∼4000, and the cationic were two quaternary alkyl ammonium derived polymers, with Mw ∼150,000 and ∼7600. The anionic polyelectrolyte has been found to be very effective in the alkalyne pH range, where the carboxylic groups are ionised. As result, the suspension is electrostatically stabilised, and the yield stress values and viscosities are very low. The adsorption and effectiveness of this polyelectrolyte could be reinforced by the presence of Ba2+ ions adsorbed on the surface of the BaTiO3 particles. The cationic polyelectrolytes, on the contrary, are not effective stabilising the suspension: at alkaline pH, the long chain polymer has the tendency to bridge particles, and the short polymer does not generate ζ 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.