WETTING TRANSITION OF N-ALKANES ON CONCENTRATED AQUEOUS SALT-SOLUTIONS - LINE TENSION EFFECT

The spreading of n-octane droplet at the surface of sodium chloride aq ueous solutions was investigated as a function of the salt concentrati on in a saturated closed cell. As long as the salt concentration is lo wer than 1.2 M, the macroscopic drop takes the form of a lens in a sta ble coexistence with its adsorbed thin film. A wetting transition occu rs for a salt concentration of about 3 M: spreading is considerably en hanced and the lens becomes a metastable pancake with a contact angle smaller than 1 degrees. After a few hours, it breaks up into a multitu de of stable microdroplets which disappear 24 h later. Drop size depen dent contact angles reveal a salt concentration dependent positive lin e tension. The values of line tension are very near. the-theoretical v alue. It is confirmed that the positive line tension stabilizes the mi crodroplets. The discussion of the results is based on the specific be havior of the interaction free energy Delta F of the oil due to the ve ry high salt concentration of the liquid substrate.