The influence of adsorbed layers on the rheological behavior of titanium dioxide dispersions

The aim of this study is to relate the influence of stearic acid on the rheological behaviour of titanium dioxide dispersions in alkyd resin solutions to the composition of the adsorbed layer on the dispersed particles.The adsorption of alkyd resin was studied using gel permeation chromatography. From the differences occurring in the molecular size distributions of the initial resin and the residual resin after adsorption, it followed that the adsorbed molecules extended throughout the whole molecular size distribution with a maximum at an equivalent chain length of 2800 Å.Stearic acid adsorption — determined using a radioactive tracer technique — was reduced by the presence of alkyd resin in the system.Titanium dioxide dispersions in alkyd resin solutions exhibited Newtonian rheological behaviour, showing that the adsorbed resin molecules protected the dispersed particles very well against flocculation. By counteracting the alkyd resin adsorption, the presence of stearic acid in the systems induced flocculation, leading to Bingham rheological behaviour. A direct relationship was shown to exist between the obtained Bingham yield values and the stearic acid adsorption.