Abstract
The surface freezing (SF) of liquid 6-perfluorohexyl hexanol (F6H6OH)–1-dodecanol (C12OH) mixture was studied by surface tension, external reflection absorption FTIR (ERA-FTIR), and X-ray reflectivity (XR) measurements. The surface tension vs. temperature curve of pure C12OH liquid shows a sharp break point at the surface liquid (SL)–SF phase transition temperature Ts. The surface tension of pure F6H6OH, on the other hand, decreases monotonically with increasing temperature. The entropy of surface formation in the SF state of C12OH is large negative due to a well-ordered structure at the surface. The electron density profile determined by XR showed that the C12OH molecules form bilayer stabilized by the hydrogen bonding between hydroxyl groups facing each other through water molecule intercalated in between them. In the F6H6OH–C12OH system, the estimation of surface composition indicated that the SL state is enriched in F6H6OH compared to bulk liquid. The negative excess entropy in the SL layer suggests that F6H6OH molecules form domains at the surface. Furthermore, the surface composition and electron density profile in the SF state indicated that a small amount of F6H6OH mix with C12OH in the SF bilayer in which F6H6OH molecules preferentially exist in the upper layer of the bilayer.
Published Version
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