Mechanism of film formation of latices

Abstract

Abstract The following mechanism is proposed for latex film formation. Initially, the latex particles move about freely, with characteristic Brownian motion. As the water evaporates, their motion becomes more restricted, and eventually the water‐air interfacial tension forces them together in a packed array, with their double layers hindering their further mutual approach. The continued evaporation of the water exerts a force to overcome this repulsion, so that the double layers are ‘ruptured’ and a polymer‐polymer contact is formed. This brings the polymer‐water interfacial tension into play, to reinforce and complement the water‐air interfacial tension. If the combined forces are sufficient to deform the polymer spheres, they form a continuous film. This film becomes more homogeneous upon ageing; there occurs a further gradual coalescence, the rate of which depends upon the polymer structure and during which any incompatible substance is exuded to the surface.