Order parameter in the nematic-isotropic phase transition

The parallel (k∥) and perpendicular (k⊥) absorption coefficients as well as extraordinary (n⊥) and ordinary (n⊥) refractive indices are determined near the calamitic nematic (NC)-isotropic (I) phase transition. We have made these measurements in a lyotropic mixture of sodium dodecyl sulfate, decanol (DeOH) and D2O via spectrophotometry and refractometry techniques. Refractive index data near the reentrant isotropic (IRE)-NC and NC-I phase transitions in a lyotropic mixture of potassium laurate, DeOH and D2O are also presented. The order parameter (S) is determined from the dichroic ratio (R = k∥/k⊥). The parameter S is also obtained from absorption coefficients and extraordinary (n∥)/ordinary (n⊥) refractive index data. The magnitude and temperature dependence of the parameter S near these phase transitions are reported. The results are discussed and compared to other nematic liquid crystals.