Tuning substrate surface energies for blends of polystyrene and poly(methyl methacrylate)

We compare the efficacies of three preparation methods intended to create in an easy and inexpensive way a nonpreferential surface for a two-component homopolymer blend of polystyrene and poly(methyl methacrylate). The first method is to physically absorb two different high molecular weight copolymers of styrene and methyl methacrylate onto hydroxylated silicon oxide. The second method consists of covalently bonding octyltrichlorosilane onto hydroxylated silicon oxide with gradient coverage to create a region with a neutral surface. The third method utilizes hydroxyl terminated, miscible, low molecular weight homopolymers of polystyrene and poly(methyl methacrylate) covalently attached to the substrate. We characterize the relative effectiveness of all three methods and their temporal stability using optical microscopy, atomic force microscopy, contact angle measurements, as well as near edge X-ray absorption fine structure (NEXAFS) microscopy and spectroscopy. The preparation methods explored should be extendable to a number of polymer systems.