Recent studies of particle packing in organic coatings

Organic coatings often contain sufficient pigmentation that the pigment vol ume concentration (PVC) and the critical PVC (CPVC) must be carefully consi dered. Past work has shown that the CPVC can be identified with the random densest packing of pigment particles after considerations of the adsorbed p olymer layer on the particles is taken into account, and that this packing can be predicted by empirical particle packing algorithms developed for mix tures of particle sizes. Recent studies have shown that local fluctuations of pigment and polymer concentrations in a film can lead to local film volu mes that can exceed the CPVC even though the average PVC for the whole film (the global PVC) is below the CPVC. These effects are consistent with obse rvations of void formation in films below the CPVC, and can be analyzed by local film statistics. We have also recently performed simulations of parti cle packing by the compression of multiple hard spheres that allows further insight into local concentration fluctuations in PVC within a film. (C) 19 99 Elsevier Science S.A. All rights reserved.