We derive the free energy of a bulk twohyphen;component polymer blend in the presence of a planar surface, and use these results to map out the region of critical wetting in parameter space. Unlike previous investigations of wetting, our free energy has terms containing gradients of the composition profile at the surface, and we find that these terms have important consequences for critical wetting. In particular, the single gradient term causes the region of parameter space in which it is possible to find critical wetting to be greatly reduced. Although, as discussed in our concluding remarks, we find that the random phase approximation fails for a polymer blend near a surface, our conclusions concerning critical wetting are valid for a free energy which includes gradient terms of the general type considered here.
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