CROSSOVER TEMPERATURE T-o FOR UNIAXIAL CALAMITIC NEMATIC MIXTURE

DOI: 10.18083/LCAppl.2022.1.67

The crossover temperature T-o corresponds to the minimum point at the dependence n(o)(T) of the ordinary refractive index for uniaxial liquid crystal. The temperature dependences of the extraordinary refractive index n(e)(T) and the birefringence Delta n(T) = n(e) - n(o) have no peculiarities at this point. For uniaxial nematic mesogen, the coefficients of the function Delta n(T) = Delta n(0)(1 - T/T-1)(beta) and the value Delta T-o = T-1 - T-o are of practical interest. The use of nematic mixtures makes it possible to vary these parameters in order to optimize operating characteristics of material. This work is devoted to determining the parameters Delta T-o and beta for calamitic nematic mixture consisting of different calamitic nematics of sort alpha with known parameters {p(alpha)} = {Delta T-o alpha, beta(alpha), B-1((alpha))}, where B-1((alpha)) = d n(T)(alpha)/dT, n (alpha) = (n(e) + 2n(o))(alpha)/3. The values Delta T-o and beta are shown to depend on the volume fractions phi(alpha) of the mixed components and parameters {p(alpha)}. The equation for determining Delta T-o was derived and its solutions were found for three binary nematic mixtures with different sets {p(alpha)}. Nonlinear dependences Delta T-o(phi(alpha)) and beta(phi(alpha)) for these mixtures were studied.