Bend and splay elastic constants at a reentrant isotropic-calamitic-nematic phase transition

By measuring the ratio between the major and minor axes of closed elliptical loops created by a magnetic field, the ratio between the bend (K33) and splay (K11) elastic constants of a lyotropic mixture of potassium laurate, decanol, and water in the calamitic nematic phase is measured as a function of temperature. Since these systems present two nematic-isotropic phase transitions--the usual one, at high temperatures, and a reentrant one, at low temperatures--such measurements are used to compare the behavior of these elastic constants at the neighborhoods of these two distinct regions, which have in common the vanishing of the order parameter. The experimental data have revealed the existence of two elastic constant branches, characterizing a distinct low- and high-temperature behavior. To explain such asymmetry we support that, because of the lyotropic nature of the compound, the micellar variation, which is mainly responsible for the reentrant phase, plays a distinct role at these two phase transitions.