Effect of a labile under layer on phase separation of PS-PMMA blend

The on-demand surface modification utilizing phase separation in blend polymer has a variety of applications like fabrication of antireflection coatings, self-cleaning and super-hydrophobic surfaces, robust membrane materials, microelectronic fabrication, etc. In the present study, a simple process has been presented for surface modification using complex polymeric structures. The study utilizes a polymer-polymer bilayer system in which the bottom layer consists of either polystyrene (PS), polymethyl methacrylate (PMMA), PS-PMMA blend, or a random copolymer (RCP), and the top layer being a blend of PS and PMMA. There is strong evidence that the nature of a labile under-layer polymer affects the phase separation of the bilayer and the overall morphology. For instance, when a blend of polystyrene (PS)-polymethyl methacrylate (PMMA) in toluene was spun coat over thin layers of PMMA, blend or RCP, no phase separation was observed. However, the phase separation took place in the case when the PS-PMMA blend was spun coat on PS (h ~ 20 nm). Arguably, the surface energy of the polymer present in the bottom layer strongly affects the phase inversion in the blend top layer. Later, by selective solvent etching, fascinating patterns were generated as characterized by atomic force microscopy. This providing the generic guidelines for complex pattern generation using different polymer combinations with distinct functionalities.

Figure showing (a) Schematic representation and (b) corresponding atomic force microscopy image of phase separation occurring in PS-PMMA blend coated over labile PS layer.