Surface morphology and wetting behavior of poly(α-methylstyrene) thin films prepared by vacuum deposition

Poly(a-methylstyrene) of various molecular weights was vacuum-deposited on different substrates including glass, gold, and silicon. The effects of substrate type, as well as the molecular weight of the polymer, on the morphology and wettability of the deposited films were investigated. The advancing and receding contact angles of water on the surfaces were measured by the method of Wilhelmy plate. Besides, the film surfaces were characterized with scanning electron microscopy and electron spectroscopy for chemical analysis.. The results show that the growth of the polymer on gold tends to be of the Stranski-Krastanov mode, in which the growth leads to a smoother geometry. On the other hand, the growth on glass and silicon shows the island mode and results in a rougher surface. The differences in diffusion coefficients and viscosities of the polymers of various molecular weights cause distinct island population and surface structure. The contact angles of water on heterogeneous films were examined, and the influence of fractional coverage was interpreted using a theoretical model.