WETTING BEHAVIOR OF A BINARY-LIQUID MIXTURE WITH A MISCIBILITY GAP INCONTACT WITH HYDROPHILIC AND HYDROPHOBIC GLASS

The morphology of coexisting liquid phases emerging from a liquid/liqu id phase separation of 2-butoxyethanol/water mixtures of critical comp osition in the instable region of the phase diagram (spinodal decompos ition) is studied using a microscope. The mixtures are confined betwee n two closely spaced and horizontally oriented hydrophilic and hydroph obic quartz plates which sire separated by a small distance d (d = 100 mu m and 200 mu m). The decomposition process is started by increasin g the temperature of the mixture from an initial temperature T-i<T-c t o a final temperature T-f>T-c (T-c, critical temperature). Wetting phe nomena are observed. In the experiments with the hydrophobic quartz pl ates a temperature difference (T-f-T-c) is found below which the wate r rich phase wets hydrophobic quartz completely. Above this temperatur e difference partial wetting of the hydrophobic quartz by the water ri ch phase is observed ((T-f-T-c) = 2.3 K). The existence of such a tem perature difference corresponds to a characteristic temperature differ ence (T-p-T-c) found in an independent study of adsorption properties of hydrophobic porous glass in contact with homogeneous 2-butoxyethano l/water mixtures in the vicinity of their liquid/liquid coexistence cu rve. At this temperature difference a characteristic change of the amo unt of substance of adsorbed water is observed.