Deposition and Characterization of Roughened Surfaces

Phase separation occurs whenever a solvent leaves a solution of strongly incompatible polymers. This can happen in bulk and in films. Films can be tailored as substrates for multiple applications such as solar cells, surface catalysis, and antireflection coatings. In this study, polystyrene (PS) was dissolved with polyvinyl acetate (PVAc) in different ratios using chlorobenzene as the solvent. Thin films of different ratios of PS and PVAc were deposited on glass via spin coating. The deposited films were investigated for their morphology, strain, surface area, and Raman scattering. The incompatibility between the two polymers leads to the growth of roughened PVAc islands supported by the PS matrix. A down shift in the Raman PVAc signal was observed in the combined film as compared with a 100% PVAc film, which was attributed to the high strain of PVAc that grew as tips. As the PVAc concentration in the polymer blend increases, the porous regions in the film expand and the amount and height of PVAc tips increase as well, up to the point where the pores merge to create a uniform surface. The optimal ratio for the deposition of a uniformly roughened surface is 75% PVAc and 25% PS. For demonstrating a possible application, we applied the partially roughened surface as a substrate for surface-enhanced Raman scattering and demonstrated at least 500% increase in the signal intensity measured in roughened areas. This is explained by the rod effect from the PVAc tips.