Measurement of the permittivity of nematic liquid crystals in magnetic and electric fields using extrapolation procedures

An analysis of the continuum equations of nematic layers subject to large electric or magnetic fields leads to simple extrapolation procedures which allow the infinite field capacitance of the layers to be inferred. For a magnetic aligning field H the reciprocal of the capacitance should be plotted against 1/H, whereas for an aligning electric voltage V the capacitance should be plotted against 1/V except in certain cases where there is a large change in the dielectric permittivities between the frequencies of the aligning and measuring electric fields, when a plot of the reciprocal of the capacitance against 1/V should be used. The optimum experiments for accurate routine measurement of both principal electric permittivities of a small sample of nematic using a single cell are identified and two experimental arrangements described.