Kinetics of formation of a surface enriched layer in an isotopic polymer blend

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Abstract
The surfaces of blends of high-molecular-weight deuterated and protonated polystyrene, after annealing above the glass-transition temperature, are enriched in the deuterated component owing to a surface energy difference between the components of isotopic origin. We have measured the kinetics of growth of the enriched layer using forward-recoil spectrometry (FRES). Following a suggestion of Lipowski and Huse, we interpret our data by assuming that the growth of the layer is diffusion limited and that the non-equilibrium layer is in local equilibrium with the edge of that region just below the surface that is depleted in deuterated polystyrene. The concentration against depth profiles that are predicted by this model as a function of annealing time are in quantitative agreement with those measured by FRES.