Elastic properties of the RIV–RIII rotator phases of alkanes Original Research Article

A model free energy has been constructed to describe the RIV–RIII rotator phase transition in alkanes in terms of the elastic strains and order parameter. The conditions for the RIV–RIII phase transition are discussed. From the free energy, the order parameter and the elastic strains are determined. The model free energy describes the first or second order character of the RIV–RIII transition depending on the strength of the coupling. The elastic properties in the vicinity of the RIV–RIII transition are discussed on the basis of a free energy expansion. The temperature dependence of the elastic constants is calculated on both sides of the transition. The coupling between the order parameter and elastic stains is shown to have a crucial influence on the phase behavior and the order of the transition.