Effect of particle surface potential and ionic strength on pigment distribution

A previous paper (Brown et al., Pi-og. Orb. Coat., 30 (1997) 185) described a computer model for simulating particle packing in pigmented latex paints using a hard sphere potential. In this paper a series of two and three dimensional computer models of particles interacting via DLVO potentials is considered. Pigment particles have a strong tendency to associate in aqueous solution because of high dispersion forces between them, related to the high refractive index of TiO2. Electrostatic stabilisation becomes ineffective if the electrolyte concentration is too high. This shows up clearly in dilute computer models of two-dimensional systems where the pigment particles begin to cluster as ionic strength increases. At very high ionic strengths the models show clustering of both pigment and latex particles. However, results from densified three-dimensional models suggest that loose clustering of pigment particles in dilute solution will not necessarily carry through to the final film. A series of paints were prepared to test the models. There was no obvious clustering of pigment particles over the range of ionic strengths used, in agreement with the three dimensional models. (C) 1997 Elsevier Science S.A.