MICROSTRUCTURE EVOLUTION IN LATEX COATINGS

Experiments of rewetting latex films by water show that latex particle deformation in the film formation processes can be reversible under certain conditions. Water roughens latex films and raises their topographic contrast. Sodium dodecyl sulfate promotes redispersion of latex particles. Fronts of rewetting are observed. Water-soluble materials appear on rewetted film. The consolidation and pore-emptying or ''dryout'' fronts of dip-coated model latex-pigment coatings are recorded. Near the consolidation front the suspension reaches the first critical concentration; near the ''dryout front,'' the suspension passes through the second critical concentration. The microstructure development in latex-pigment coatings is continuous behind the consolidation front, although the dryout front has been observed there. The slightly carboxylated poly (styrene-butadiene) latex particles deform in seconds in coatings of precipitated calcium carbonate with latex binder. The highly carboxylated poly (styrene- butadiene) latex deformed only slightly in dir-dried coating. The results indicate that latex particle deformation is not finished dt the second critical concentration.