Wetting behavior of a binary liquid mixture with a miscibility gap in contact with hydrophilic and hydrophobic glass

The morphology of coexisting liquid phases emerging from a liquid/liquid phase separation of 2-butoxyethanol/water mixtures of critical composition in the instable region of the phase diagram (spinodal decomposition) is studied using a microscope. The mixtures are confined between two closely spaced and horizontally oriented hydrophilic and hydrophobic quartz plates which sire separated by a small distance d (d = 100 mu m and 200 mu m). The decomposition process is started by increasing the temperature of the mixture from an initial temperature T-i<T-c to a final temperature T-f>T-c (T-c, critical temperature). Wetting phenomena are observed. In the experiments with the hydrophobic quartz plates a temperature difference (T-f-T-c)* is found below which the water rich phase wets hydrophobic quartz completely. Above this temperature difference partial wetting of the hydrophobic quartz by the water rich phase is observed ((T-f-T-c)* = 2.3 K). The existence of such a temperature difference corresponds to a characteristic temperature difference (T-p-T-c) found in an independent study of adsorption properties of hydrophobic porous glass in contact with homogeneous 2-butoxyethanol/water mixtures in the vicinity of their liquid/liquid coexistence curve. At this temperature difference a characteristic change of the amount of substance of adsorbed water is observed.