TEMPERATURE DEPENDENCES OF THE REFRACTIVE INDICES OF UNIAXIAL CALAMITIC LIQUID CRYSTALS WITH HIGH BIREFRINGENCE

Aver'yanov, E. M. Source: LIQUID CRYSTALS AND THEIR APPLICATION, 18 (2):53-63; 10.18083/LCAppl.2018.2.53 APR-JUN 2018

The temperature dependences of the refractive indices nj(t) and the values <n(t)> = (n|| + 2n)/3,n(t) =ε-1/2,ε= (ε|| + 2ε)/3, εj = nj2 for the light waves polarized along (j = ||) and across (j = ⊥) the director in uniaxial calamitic liquid crystals (LCs) were studied within the microscopic approach with taking into account the anisotropy of the local-field tensor fj(t) =1 + Lj(t)[εj(t)–1] and the Lorentz tensor Lj(t). The known negative derivatives <n(t)>' = d<n(t)>/dt,n' and the point to of minimum at the dependence n(t) for calamite LCs were shown to correspond to small and medium values of the birefringence Δn = n|| – n. For LCs with high values of δn and components L exceeding the threshold value L⊥e two new effects were predicted: positive derivatives <n>', and the presence of the point te of maximum at the dependence n||(t). For a number of nematics with high values of Δn the components Lj(t) were determined, the presence of the predicted effects and the conditions for their manifestation were confirmed, the values te were obtained and their connection with the magnitude Δn were established. The features of the transition from LCs with point to to LCs with point c under gradual increase in Δn were cleared up.