EFFECT OF PARTICLE SURFACE-POTENTIAL AND IONIC-STRENGTH ON PIGMENT DISTRIBUTION

A previous paper (Brown et al., Pi-og. Orb. Coat., 30 (1997) 185) desc ribed a computer model for simulating particle packing in pigmented la tex paints using a hard sphere potential. In this paper a series of tw o and three dimensional computer models of particles interacting via D LVO potentials is considered. Pigment particles have a strong tendency to associate in aqueous solution because of high dispersion forces be tween them, related to the high refractive index of TiO2. Electrostati c stabilisation becomes ineffective if the electrolyte concentration i s too high. This shows up clearly in dilute computer models of two-dim ensional systems where the pigment particles begin to cluster as ionic strength increases. At very high ionic strengths the models show clus tering of both pigment and latex particles. However, results from dens ified three-dimensional models suggest that loose clustering of pigmen t particles in dilute solution will not necessarily carry through to t he final film. A series of paints were prepared to test the models. Th ere was no obvious clustering of pigment particles over the range of i onic strengths used, in agreement with the three dimensional models. ( C) 1997 Elsevier Science S.A.