Fabrication of Micropatterned Thin Films Through Controlled Phase Separation of Polystyrene/polydimethylsiloxane Blends by Spin Coating

In this study, we blended two readily available polymers, polydimethylsiloxane (PDMS), a semi-crystalline polymer, and polystyrene (PS), an amorphous polymer, both having widely varying physical properties. The blend is then spin coated to form a thin film. We investigated the effects of relative polymer concentration, spin coating speed, and environmental factors, such as temperature, on the ultimate morphologies of the phase-separated thin films. It was found that it is possible to regulate the morphologies of the thin films to achieve desirable microstructures such as spherical droplets, holes, bi-continuous lamellar structures, and tubules by controlling the fabrication conditions. The polymer blend films with higher PS concentrations were shown to form a bilayer system with an upper PS-rich layer due to the thermodynamic instability of the film caused by the rapid evaporation of solvent, while films with higher PDMS concentrations exhibited cohesive forces that engendered microtubule formation and led to high surface roughness.