Stability of Dispersions in the Presence of Graft Copolymer (II) Adsorption of Graft Copolymers on Titanium Dioxide and the Stability and Rheology of the Resulting Dispersions

Abstract

The adsorption of two graft copolymers (Atlox 4913 and Hypermer CG-6 consisting of poly(methyl methacrylate) methacrylic acid backbone and polyethlene oxide side chains) on titanium dioxide dispersions have been investigated. Hypermer CG-6 contains more polymethcrylic acid groups in the backbone. The influence of copolymer structure, temperature, and electrolyte concentration on the stability of titanium dioxide dispersions was studied using rheological measurements and microscopy observation. The adsorbed layer thickness of copolymer on the titanium dioxide particle surface at saturation adsorption was evaluated by measuring the rheological properties of the concentrated dispersions using shear stress−shear rate and oscillatory measurements. The results showed that the adsorption behavior of copolymer on TiO2 is different from polystyrene latex which has a hydrophobic surface, especially for Atlox 4913. The dispersions showed weak flocculation when using Atlox 4913 but stable dispersions for Hypermer CG-6. For the stable dispersions using Hypermer CG-6, the adsorbed layer thickness decreased with increase in the volume fraction of the dispersion. Increasing temperature showed little effect on the viscoelastic properties. However, with the increase of electrolyte concentration, moduli increased sharply indicating flocculation of the dispersions.