Capillary condensation versus prewetting

The first-order prewetting transition that has been predicted to occur at the interface between a fluid and a single wall is investigated for the case of a fluid confined between two walls. Prewetting is found to be in competition with capillary condensation of the undersaturated gas to a liquid. The results of density-functional calculations suggest that only for wall separation H>$H_{\mathrm{triple}\left(\mathrm{T}\right)}$ will prewetting occur at larger undersaturations than condensation. For H$H_{\mathrm{triple}\left(\mathrm{T}\right)}$ coexistence between stable thick and thin films will not be observed. Since $H_{\mathrm{triple}}$ is typically 100 molecular diameters or more, this places restrictions on those adsorption experiments and computer simulations that search for prewetting.