Electric birefringence of solutions of nematic compounds

The static field Kerr electro-optic effect has been studied in solutions of the nematic liquid crystals MBBA and PCB in carbon tetrachloride. These compounds are negative and positive nematics respectively. At low field strengths, all solutions exhibited Kerr law behaviour and Kerr constants were evaluated. The dependence of these constants on concentration differed markedly between these two nematic materials. With MBBA, the birefringence and hence the Kerr constant underwent a reversal of sign from positive to negative with increasing solution concentration. With PCB, the Kerr constant was always positive. Whereas MBBA solutions always showed Kerr law behaviour for fields up to 45 kV cm^-1, the PCB solutions showed deviations from this at the higher field strengths. Combinations of higher concentrations and field strengths resulted in irregular transients in the birefringence.