Film formation of polymeric emulsions: Structure set-up and the pinhole effect characterized by microscopic techniques

Drying of emulsions of special polymeric core-shell latexes results in stru ctured films and coatings with advantageous material properties. Here, we f ocus on so-called "container particles", consisting of a low viscosity core with a low glass transition (poly(2-ethylhexyl methacrylate), PEtHMA), cov ered by a thin shell of a cross-linked rubber (poly(n-butyl acrylate), PEA) . These particles can be regarded as model emulsions of reactive polymeric oils with a very high colloidal stability. The film formation of these late xes was studied by atomic force microscopy (AFM) in the tapping mode as wel l as by transmission electron microscopy (TEM). It is shown that the films stay nanostructured after the drying process, i. e. they exhibit both a con trolled topography as well as a network superstructure originating from the characteristics of the original dispersions. TEM allows to detect the whereabouts of the polar stabilizer. Both continou s surfactant films as well as inverted micelles are found. A geometrically induced demixing phenomenon is found which enriches the polar components an d might be the molecular reason for the so-called pinhole-effect, the failu re of water-born coatings in contact with water.