Observation of hysteresis in the properties of a ternary lyotropic liquid crystal system

Abstract

We have carried out differential scanning calorimetry (DSC), electrical conductivity and mass diamagnetic susceptibility studies on sodium decylsulfate(SdS)= decanol=water system for two different concentrations of the constituents. In these concentrations, this system exhibits calamitic nematic (Nc), isotropic (I) and hexagonal (H) phases on heating from the room temperature. On heating the samples, the DSC thermograms exhibit two peaks which can be related to the reported Nc-I and I-H phase transition temperatures. However, on cooling from a high temperature they do not exhibit any peak. The temperature dependence of electrical conductivities and magnetic susceptibilities of these samples are also different while heating and on cooling. Based on our reported correlation between the susceptibility and micellar sizes in an ionic micellar system, we infer that the observed hysteresis behavior in the susceptibility in this system is related to the difference in the temperature dependence of the micellar sizes on heating and on cooling. The electrical conductivity in these ternary systems is related to the mobility of the counter ions which in turn depends on the viscosity of water. Hysteresis seen in the conductivity may be related to the changes in the viscosity of water due to the difference in the temperature dependence of the micellar sizes on heating and cooling. Incidentally, in water based nanofluids, the sizes of the suspended nanoparticles have profound influence on the viscosity of water.