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Published online by Cambridge University Press: 15 February 2011
Normal alkanes of carbon number n>14 exhibit surface crystallization at their liquid-vapor interface. This has been investigated with x-ray reflectivity, grazing incidence scattering and surface tension measurements. The structure and thermodynamics of the surface layer is consistent with a monolayer of the bulk rotator phase occurring at the surface above the bulk melting temperature. On the other hand, thin films of alkanes on SiO2, exhibit a reduction of the melting temperature. The surface crystalline phase is observed for carbon number n>14. The vanishing of surface phase for small n may be due to a transition from surface freezing to surface melting behavior. These measurements can yield the relative surface energies of the various phases.