Phase Separation,Wetting and Dewetting in PS/PVME Blend Thin Films: Dependence on Film Thickness and Composition Ratio

The effects of film thickness and composition ratio on the morphology evolution of polystyrene (PS)/poly(vinyl methyl ether) (PVME) blend thin films were investigated. Diverse morphology evolutions including droplet-matrix structure, hole emergence, bicontinuous structure formation, percolation-to-droplet transition could be observed under annealing in two-phase region, depending on film thickness and composition ratio. The mechanism for these morphology variations was related to the complex effects of phase separation, dewetting and preferential wetting. The comparison between the thickness of bottom PVME layer and the twice of gyration radius 2R_g(PVME) played a dominant role in morphology control. Only when the PS/PVME film had specific film thickness and compositional symmetry, phase separation and dewetting could happen in sequence.