Functionalizing polymer surfaces by field-induced migration of copolymer additives. 1. Role of surface energy gradients

Field-induced migration of low surface tension polystyrene-b-poly(dimethyl siloxane) (PS-b-PDMS) block copolymer additives in a polystyrene (PS) host was investigated using a series of narrow molecular weight distribution polystyrenes (5 x 10(3) < M-W,(PS) < 2 X 10(7) g/mol). Dynamic contact angle analysis (DCA) and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy measurements were used to characterize the surface chemical make-up of polymer/additive blends created by solvent casting, precipitation, and melt annealing processes. For all host PS molecular weights investigated, selective dimethyl siloxane (DMS) enrichment of the air/polymer interface was observed. Near saturation levels of DMS surface coverage were found in PS/PS-b-PDMS blends with bulk copolymer additive compositions as low as 2 wt %. The surface excess concentration of DMS groups Delta phi (DMS) in these blends could be manipulated, however, by careful selection of the host PS and PS-b-PDMS additive molecular weight, annealing conditions, and physicochemical properties of materials comprising the bounding interfaces. The effect of the first two factors on Delta phi (DMS) can be summarized by an approximate scaling relation, Delta phi (DMS) similar to M-wPS alpha, where the scaling exponent ct is a function of annealing conditions. For unannealed PS/PS-b-PDMS blend samples, alpha approximate to -0.5, whereas for samples annealed for prolonged periods at elevated temperatures a values in the range 0.1-0.15 were found. Surprisingly, PS/PS-b-PDMS blend samples annealed at elevated temperatures near enhanced DMS concentration at the polymer/metal of the molecular weight dependence of diffusivity, host polystyrene.