Influence of dispersant functional group architecture on titania pigment particle interactions

Abstract

Ensuring discrete dispersion of pigment particles is crucial to maintain their separation during processing and storage, and to achieve the desired properties in coatings. To facilitate dispersion and prevent aggregation, the stability of the dispersant along with the chemical interaction between pigment particles and dispersants is critical. This study was conducted to investigate the interaction between robust dispersants containing thermally stable carboxylate and phosphonate functional groups and the titania pigment surface at pH values experienced in pigment manufacturing as well as in application. The study found that the interaction depends on the type of group, the distribution density of the group, and the solution pH. Dispersant adsorption can occur under both alkaline and acidic solution conditions, with the adsorption density increasing when the pH is reduced or the carboxylate group density is increased. At pH 9.5, dispersant adsorption affinity and density is low, and hydrogen bonding occurs in addition to phosphate group chemisorption. At pH 5.5, both the adsorption affinity and density significantly increase due to electrostatic interactions between carboxylate and/or phosphonate groups and the pigment surface, combined with phosphate group driven chemisorption. Linear carboxylate-phosphonate copolymers and carboxylate dispersants present at the pigment surface provide electrostatic stabilisation while branched copolymers provide both electrostatic and steric stabilisation. The synergistic physical and chemical interaction combined with dispersion stability may lead to improved titania pigment suspensions using branched copolymer dispersants.