Wetting and autophobicity of a polymer melt on a network of itself

Wetting properties of thin films of a polymer melt on top of a network formed by irradiation cross-linking of an identical melt were studied. The permeability of the network and its wettability as a function of the extent of cross-linking were characterized by nuclear reaction analysis, atomic force microscopy, contact-mechanics measurements of the adhesion energy, and light microscopy. As the degree of cross-linking increased, we observed a crossover from complete to partial wetting, followed by a second crossover back to complete wetting at higher cross-link densities. We suggest that the first crossover is a manifestation of entropy-induced autophobicity arising from the brush-like nature of the cross-linked surface, while the second originates from surface roughening induced by the cross-linking.