Temperature Behavior of the Order-Parameter Invariants in the Uniaxial and Biaxial Nematic Phases of a Lyotropic Liquid Crystal

Abstract

Conoscopic observations have been made on a mixture of potassium laurate, 1-decanol, and D2O in the discotic-uniaxial, biaxial, and cylindric-uniaxial nematic phases. The differences between the principal refractive indices have been measured, leading to a complete determination of the tensor order parameter in all the three phases. In the biaxial phase, the symmetric invariants of the order parameter are found to have a linear dependence on temperature, in good agreement with the prediction of the mean-field model.

Nonlinear optical properties of liquid crystals probed by Z-scan technique

“…Usually, temperature-driven transitions are determined measuring the linear birefringence by polarized optical microscopy. The dielectric tensor ← → can be written as function of the linear birefringences ∆n L and δn L [39]. The measurement of the linear birefringences around the transition temperature (T c ), give informations about the collective behavior of the basic units (molecules or micelles) of the system.…”

“…The measurement of the linear birefringences around the transition temperature (T c ), give informations about the collective behavior of the basic units (molecules or micelles) of the system. Galerne et al [39] show that the N c − I (here, I states for the isotropic phase) phase transition is weakly first-order and the linear birefringence has a discontinuity at T cI (here, T cI states for the N c − I transition temperature). On the other hand, the N c − N bx phase transition is second-order and mean-field.…”

Temperature-concentration behaviour of the order parameter in the nematic phases of a lyotropic liquid crystal

“…[5] and references therein). On the contrary, the first observation of the biaxial nematic phase (NBX) is recent [3], and little information is available on it to-date [6].…”

Measurements of optical anisotropy of a calamitic lyotropic liquid crystal

“…Measurements of the extraordinary (n e ) and ordinary (n o ) refractive indexes as function of temperature are important parameters to study the phase transitions in liquid crystals and some data are available for lyotropic liquid crystals [6] [7] [8] [9] . In this paper we report measurements of temperature dependence of the anisotropy of refractive indexes of a calamitic mixture containing sodium lauryl sulphate (SLS)/ decanol /water, in the nematic phase.…”