External normal pressure prevents preferential wetting of PS/PMMA blend thin films

Substrate wetting of the component(s) of thin polymer blend films strongly dictates their phase evolution during thermal annealing. In the case of wetting by one component being preferential than the other, a continuous wetting layer at the substrate will form. Here, we report that the preferential wetting of PMMA within a PS/PMMA thin film can be prevented under normal pressure. Moreover, the external pressure drives the PMMA wetting layer at the substrate (or a PMMA cushion layer intentionally placed between the blend film and the superstrate) into the isolated PMMA domains within the blend film. This results in a film morphology normally observed on neutral surfaces, revealing that normal pressure can potentially be used to effectively control the blend film morphology by preventing the hydrodynamic wetting.