Evolution of surface structure and chemistry of pigmented coatings during drying

Pigmented coatings made of styrene-butadiene (SB) latex and kaolin clay wit h a wide range of pigment volume concentration (PVC) were quenched and free ze-dried at different stages of film formation. The surface was characteriz ed by XPS, SEM, gloss and surface energy measurements. The SB/clay ratio in creased at the surface with drying time; The latex-pigment interaction at t he surface, at and below the critical pigment volume concentration (CPVC), is different from that above CPVC. While at and below CPVC latex coalescenc e is almost complete at the second critical concentration (SCC), where air enters into the coating, above CPVC latex continues coalescing after SCC. T his behavior of latex coalescence at the surface above CPVC is different fr om that found in the bulk. Even at PVC as low as 40%, XPS results indicate that the surface is still heterogeneous and not covered totally with latex. Surface energy and its polar component decreased during film formation. (C ) 2000 Elsevier Science S.A. All rights reserved.