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Wetting of Surfactant Solutions by Alkanes
Author(s) -
Wilkinson Katherine M.,
Bain Colin D.,
Matsubara Hiroki,
Aratono Makoto
Publication year - 2005
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200400514
Subject(s) - wetting , pulmonary surfactant , contact angle , wetting transition , hexadecane , chemistry , surface tension , alkane , monolayer , dodecane , ellipsometry , chromatography , analytical chemistry (journal) , thermodynamics , materials science , organic chemistry , hydrocarbon , composite material , nanotechnology , thin film , biochemistry , physics
Ellipsometry, surface tensiometry, and contact‐angle measurement have been used to study the transition between partial wetting and pseudo‐partial wetting of surfactant solutions by alkanes. In the partial wetting regime, the air–water surface tension is the same with and without alkane. In the pseudo‐partial wetting regime, the air–water surface tension is lowered by the presence of alkane, showing that oil is solubilised into the surfactant monolayer. A discontinuous change in the coefficient of ellipticity with increasing surfactant concentration provides unequivocal evidence for the first‐order nature of the wetting transitions. Ellipsometry has been used to explore the generality of wetting transitions of alkanes (dodecane, hexadecane, and squalane) on surfactant solutions [dodecyltrimethylammonium bromide, tetredecyltrimethylammonium bromide, dibucaine hydrochloride, and Aerosol OT (AOT)]. Of the systems studied, only hexadecane on AOT solutions did not show a wetting transition. Excess alkane remains as a lens on the surface of the surfactant solutions at all concentrations, but the contact angle is a minimum at the wetting transition. A semiquantitative model for the variation of the contact angle with surfactant concentration is provided.