Modification of a polystyrene brush layer by insertion of poly(methyl methacrylate) molecules

The ability to tune the wetting behavior of poly(styrene-block-methyl methacrylate) on a polystyrene (PS) brush by insertion of hydroxyl-terminated poly(methyl methacrylate) (PMMA-OH) was demonstrated. The brush properties before and after insertion of PMMA-OH were studied with goniometry, ellipsometry, near edge x-ray absorption fine structure spectroscopy, and scanning electron microscopy. The initial PS brush served as a barrier to the grafting of PMMA onto the substrate. The amount of PMMA that could penetrate through the PS brush barrier and graft onto the substrate depended on the initial PS brush thickness. As a result, the PS:PMMA ratio in the final composite brush, and therefore the brush wetting properties, could be carefully controlled. The final composition also depended on the grafting sequence of the brush molecules. This may offer a generalized approach for fabricating neutral brush surfaces without requiring the synthesis of specific random copolymers.