title: Surfactant-induced phases in water-supported alkane monolayers: II. Structure.
abstract: The structure of the Langmuir-Gibbs films of normal alkanes C(n) of length n = 12-21 formed at the surface of aqueous solutions of C(m)TAB surfactants, m = 14, 16, and 18, was studied by surface-specific synchrotron X-ray methods. At high temperatures, a laterally disordered monolayer of mixed alkane molecules and surface-adsorbed surfactant tails is found, having thicknesses well below those of the alkanes' and surfactant tails' extended length. The mixed monolayer undergoes a freezing transition at a temperature T(s)(n,m), which forms, for n ≤ m + 1, a crystalline monolayer of mixed alkane molecules and surfactant tails. For n ≥ m + 2, a bilayer forms, consisting of an upper pure-alkane, crystalline monolayer and a lower liquidlike monolayer. The crystalline monolayer in both cases consists of hexagonally packed extended, surface-normal-aligned chains. The hexagonal lattice constant is found to decrease with increasing n. The films' structure is discussed in conjunction with their thermodynamic properties presented in an accompanying paper.
authors.affiliation: Physics Department and Institute of Nanotechnology, Bar-Ilan University , Ramat-Gan 52900, Israel.
authors.forename: Shai
authors.initials: S
authors.lastname: Yefet
authors.forename: Eli
authors.initials: E
authors.lastname: Sloutskin
authors.forename: Lilach
authors.initials: L
authors.lastname: Tamam
authors.forename: Zvi
authors.initials: Z
authors.lastname: Sapir
authors.forename: Moshe
authors.initials: M
authors.lastname: Deutsch
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Ocko