Wetting of a polymer brush, a system with pronounced critical wetting

We consider a polymer brush composed of units of type P, at a solid substra te S in an incompatible binary A/L solvent mixture. At A/L coexistence the film thickness of the wetting component A depends mainly on the second viri al coefficient v(AP) of polymer-polymer contacts in an A-rich phase: with i ncreasing v(AP) the film thickness jumps from a microscopic to a mesoscopic value and then continues to grow proportionally to v(AP). The film grows s moothly without bounds when the fluid interface is further out than the seg ments of the brush chains can reach. This escape of the A-L interface from the brush coincides with the (second-order) wetting transition and occurs a t v(AP)(W). Substrates covered by a polymer brush are excellent surfaces or der to measure critical wetting because the wetting behavior can be tuned i ndependently from the short-range interactions of the solvents with the sol id substrate. For relatively thin brushes, van der Waals contributions can seriously modify these predictions. However, as the brush thickness is prop ortional to the chain length N, the relative contribution of these forces c an be tuned; i.e., for a sufficiently large blush height the (long-range) v an der Waals forces can be ignored. The wetting scenario has been elaborate d by a numerical self-consistent-field theory for inhomogeneous polymer sys tems.