TEMPERATURE BEHAVIOR OF REFRACTIVE INDICES OF DISCOTIC NEMATICS WITH HIGH BIREFRINGENCE

Aver'yanov, E. M. Source: LIQUID CRYSTALS AND THEIR APPLICATION, 18 (3):37-44; 10.18083/LCAppl.2018.3.37 JUL-SEP 2018

Temperature behavior of refractive indices nj(t) and values of <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 discotic nematics ND was studied within the microscopic approach with accounting for 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, and the point te of minimum at the dependence n||(t) for nematics ND were shown to correspond to small and medium values of the birefringence Δn = n|| – n. For nematics ND with high values of Δn and components L less than the threshold value L⊥o(nj), two new effects were predicted: positive derivatives <n>',

n

' and the presence of the maximum point to at the dependence n(t). The correlation of to with the magnitude of Δn(to) and the dependence Δn(λ) on the light wavelength λ was established. The features of the transition from objects with point te to objects with point to under gradual increase of Δn were cleared up. The molecules were pointed for which one could expect the presence of the predicted effects. The role of these effects in the improvement of visual characteristics of liquid crystal displays with nematic ND in the boundary compensation film was observed.