THEORY OF SURFACE FREEZING OF ALKANES

A fluctuation-based entropic scenario for the explanation of surface f reezing in normal alkanes is proposed. The model is based on the notio n that strong fluctuations along the molecular axis of uniaxially orde red stretched chains, can exist in a solid monolayer on top of a liqui d phase and provide sufficient entropy to stabilize it against the for mation of a bulk rotator phase, in which such fluctuations are suppres sed by the presence of neighboring layers. We show that the phenomenon can exist only in a restricted range of molecular weights, and calcul ate the molecular weight dependences of the temperature range in which it is observed and of the correction to the surface tension of the li quid due to the presence of the solid surface layer. The roughness of solid surface monolayer is also calculated. The results are in agreeme nt with recent experiments.