Evidence of Tricritical Behavior at the Nematic Isotropic Transition

Abstract

Tricritical behavior at the nematic–isotropic phase transition is discussed by means of Landau–de Gennes phenomenological theory. The temperature difference TNI-T*is obtained near the tricritical point. We also obtained the value of the ratio (Q*-QNI)/QNI, where Q*is the order parameter at the temperature T*of the absolute stability limit of the isotropic phase and QNIis the order parameter at the nematic–isotropic transition temperature TNI. As a definite improvement over the earlier attempts utilizing Landau–de Gennes scheme the present work can reproduce low values of (Q*-QNI)/QNIand that of TNI-T*as demanded by experimental observations. The tricritical exponents are calculated from the scaling theory and compared with observed values. Using the Ginzburg criterion, we also determine the critical region of the nematic–isotropic phase transition.