A novel surface induced phase transition in normal alkane fluids

Abstract

Light scattering from thermally excited capillary waves has been used to study normal liquid alkanes (15 to 18 carbon atoms in length) as a function of temperature. In all cases the frequency and damping of the surface waves exhibit well-defined discontinuities at a temperature near, but distinct from the melting point. Above that temperature the dat behave as expected for a clean liquid surface; below it they are consistent with predictions for fluid having a structured surface layer through which the surface excess viscoelastic modulus is negative in magnitude. The phenomena suggest the occurrence of a surface-induced phase transition, in which the conformational degrees of freedom of molecules close to the surface are inhibited.