The birefringence of thin films of some nematic liquid crystals

Birefringence and birefringence dispersion of N-(p-methoxy-benziliden)-p- n'-butylaniline (MBBA) as well as of poly-(pheny-methacrylic)-ester of cetyloxybenzoic-acid (PPMAECOBA) in tetrachloromethane (TCM) thin films have been determined. Measurements have been made, at room temperature, by two methods: interferometrically in monochromatic light and from the visible channeled spectra of thin layers. The dependence of the main refractive indices on light wavenumbers has been established using interferometrically estimated data. Having in view the good agreement between the birefringence computed with this dependence and the birefringence estimated from the visible channeled spectra, we consider that the established formulas could be used to give the visible main refractive indices of the studied NLC.