A. Dussaud et M. Vignesadler, WETTING TRANSITION OF N-ALKANES ON CONCENTRATED AQUEOUS SALT-SOLUTIONS - LINE TENSION EFFECT, Langmuir, 13(3), 1997, pp. 581-589
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.