Mechanism of TiO2 stabilization by low molecular weight NaPAA in reference to water-borne paint suspensions

The effect of sodium polyacrylate (NaPAA), generally used as a dispersant in paint formulations, on the stability of zirconia- and alumina-coated TiO2 suspensions was investigated. The effect of percent solids and medium pH on NaPAA adsorption along with electrokinetics, rheology and stability in TiO2/NaPAA systems was systematically studied to understand the suspension properties of TiO2 under various conditions. Adsorption on the TiO2/NaPAA system exhibits a plateau, which decreases with increasing percent solids and medium pH and follows the Langmuir equation. The presence of a stable region above the plateau concentration is in good agreement with viscosity and zeta potential measurements. Zeta potential values of TiO2 are high enough to provide an appropriate dispersion in the plateau region. It is shown that stabilization of TiO2 suspensions with appropriate adsorption of NaPAA is achieved through electrosteric stabilization. The medium pH on stability of the system is particularly critical. Maximum stabilization is obtained at pH values where the presence of anionic carboxylate groups of NaPAA is available in loops–tail conformation.