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 × 103 < Mw,PS < 2 × 107 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 ΔφDMS 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 ΔφDMS can be summarized by an approximate scaling relation, ΔφDMS ∼ MwPSα, where the scaling exponent α is a function of annealing conditions. For unannealed PS/PS-b-PDMS blend samples, α ≈ −0.5, whereas for samples annealed for prolonged periods at elevated temperatures α values in the range 0.1−0.15 were found. Surprisingly, PS/PS-b-PDMS blend samples annealed at elevated temperatures near high-energy aluminum substrates also manifested enhanced DMS concentration at the polymer/metal interface. These observations are discussed in terms of the molecular weight dependence of diffusivity, surface tension, and configurational entropy of the host polystyrene.