B.S.E. Thesis Research:
The ability of block copolymers to self-assemble into regular structures on the nanometer scale makes them ideal materials for nanolithographic templates and fabrication of nanodevices. In order to utilize nanostructures such as cylinders and lamellae in a block copolymer thin film, these structures must be oriented perpendicular to the surface. Previous studies have shown that inserting a random terpolymer brush between the block copolymer and substrate is a simple and effective method to neutralize the surface and induce perpendicular orientation. Tuning terpolymer composition regulates the wetting behavior of the block copolymer components. In the present study, statistical terpolymers of styrene (S), methyl methacrylate (MMA), and 2-hydroxyethyl methacrylate (HEMA) were synthesized through classical free radical polymerization to regulate the orientation of block copolymers of PS and PMMA. Unlike methods used in previous studies, conversion was limited to 25% to minimize drift in polymer composition. Terpolymer HEMA mole fraction was set to 0.03, and styrene mole fraction was varied from 0.64 to 0.52, in order to investigate the styrene composition that allows perpendicular morphology in lamellar and cylinder forming block copolymers. Scanning electron microscopy (SEM) and optical imaging showed that none of the composition tested produced uniform perpendicular morphology. Instead, terracing and preferential wetting were observed in all samples.