Film formation with latex particles

The coalescence of latex particles is investigated through small-angle neutron scattering and electron microscopy. The particles are made of a soft polymeric core protected by a hydrophilic membrane, and they are dispersed in water. This dispersion is spread on a substrate, and water is removed to form a dry film. As the membranes of neighboring particles come into contact, they may break up to allow fusion of the particle cores. This is found to occur when the membranes are made of short-chain surfactant molecules; then all hydrophilic material is expelled to the film surface or to large isolated lumps. Alternatively, the membranes may remain until the film is completely dry; this is found to occur when they are made of hydrophilic polymers which are grafted onto the core. Hence, the fusion of particles is controlled by the connectivity of membranes.