Wetting properties of thin liquid polyethylene propylene films

Polyethylene propylene films of various molecular weights, which would normally wet native-oxide-covered Si surfaces, were observed to dewet the surface when the film thickness became less than the polymer radius of gyration. These films could be made to wet either by increasing the annealing temperature or by chemically modifying the surface. The results are shown to be consistent with an expression for the spreading parameter that incorporates a stretching free energy term for the polymer chains. Measurements of the diffusion constant of the polymer on the silica surface indicated that an activation energy was required to desorb the polymer segments from the surface before diffusion could occur.