Adsorption and Grafting: the formation of thin layers of polystyrene and poly-(S-HEMA) on silicon dioxide surfaces

Abstract

By forming a new interface between the original substrate and the environment, polymer brushes are able to modify the intermolecular interactions between other molecules and the target surface. This makes them ideal materials for use in a wide variety of applications involving the adsorption of target molecules on a surface, such as chromatography and biocompatible materials. Apart from the choice of polymer, the interaction between a polymer brush and other molecules is dependent on physical properties of the brush, notably its thickness. The tuning of brush thickness is usually cumbersome – for instance, previous studies have controlled brush thickness by tagging the polymer ends with charged units, immersing the brush in solvent, and varying the electrolyte concentration in the solvent. This paper seeks to examine a more convenient method of controlling brush thickness. Styrene (S) homopolymers and copolymers of styrene (S) and 2-hydroxyethyl methacrylate (HEMA) with HEMA mole fractions ranging from 0.022 to 0.139 were synthesized via free radical polymerization. Spin-coated polymer films were annealed at temperatures ranging from 130 – 170° C for annealing times of 0 – 32 hours. This paper demonstrates that film thickness of the grafted poly(S-HEMA) is much greater than that of polystyrene at all annealing temperatures and times considered, and that poly(S-HEMA) film thickness increases with rising HEMA content.