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The wavelength-dependent optical transmission and birefringence of lyotropic nematic calamitic mesophase under a polarising microscope and its order parameter in comparison to Michel-Lévy interference colour chart

ABSTRACT In the present study, the optical transmissions of lyotropic nematic calamitic mesophase (NC) were measured depending on temperature for wavelengths of 440, 470, 510 and 694.3 nm in visible spectrum using polarised microscopy. For each wavelength, the birefringence was determined in the NC mesophase temperature region and it was observed that the smaller the wavelength in the visible region, the greater the birefringence. Using the birefringence, macroscopic order parameter was obtained depending on temperature and it was found to be approximately the same for each wavelength. Besides, the textural colour properties of the planar-oriented sample were observed under the microscope throughout the mesophase region. These colour attributes were compared with the Michel-Lévy interference chart and the birefringence was sensitively determined from the chart. This time, the order parameter was studied using the birefringence found from the chart. It was approximately the same as the order parameter found using the microscopy. Graphical abstract