Theory of surface freezing of alkanes

A fluctuation-based entropic scenario for the explanation of surface freezing in normal alkanes is proposed. The model is based on the notion that strong fluctuations along the molecular axis of uniaxially ordered stretched chains, can exist in a solid monolayer on top of a liquid phase and provide sufficient entropy to stabilize it against the formation of a bulk rotator phase, in which such fluctuations are suppressed by the presence of neighboring layers. We show that the phenomenon can exist only in a restricted range of molecular weights, and calculate the molecular weight dependences of the temperature range in which it is observed and of the correction to the surface tension of the liquid due to the presence of the solid surface layer. The roughness of solid surface monolayer is also calculated. The results are in agreement with recent experiments.