Differential dichroic spectroscopy in liquid crystals using unpolarized radiation

Abstract

An unpolarized, differential technique is described for obtaining the dichroic spectra of uniaxial liquid crystals from a single spectral scan. Using this method, we investigate the near infrared dichoic spectrum of n-heptyl cyanobiphenyl (7CB). The temperature dependence of the orientational order parameter has been derived close to the nematic-isotropic transition and this is in good agreement with earlier Raman data. The differential method is also advantageous for dichroic studies on oriented guest molecules in liquid crystals. Illustrative results are presented for p-nitrotoluene dissolved in a nematic medium.