Refractive indices and order parameter studies of nematic liquid crystal mixtures

Measurement of ordinary refractive index(no) and birefringence (An) have been made on two nematic liquid crystal mixtures : ZLI 3497-100 and ZLI 3741 in their mesophases. From these measurements, the extra-ordinary refractive index (n(e)), the microscopic order parameter (S) and normalized polarizabilities [GRAPHICS] are evaluated at different temperatures. The normalized extra ordinary polarizability (alpha(c)/alpha) , the order parameter (S) and the factor f ( = alpha(c)/alpha(0)) fall with rise in temperature for both the mesogens, which may be due to the orientation of the long molecular axis with respect to the director and also due to the buckling of the end groups in the molecules. The difference in the optical properties can be attributed to the additional cyclohexyl cyclohexane and aromatic ester components in ZLI 3497-100.