Complex Strain-Optical Coefficient Measurements by Means of Polarization Analysis of a Diffracted Light by Longitudinal Ultrasound

Abstract

The theory to obtain the complex strain-optical coefficients was described for the liquids from polarization analysis of a diffracted light by longitudinal ultrasound. The polarization analyses on the isotropic phase of liquid crystal, 4-cyano-4'-pentylbiphenyl (5CB) were carried out at 40, 50 and 60 °C in the frequency range from 5 to 25 MHz. For the +1st and −1st order diffracted lights, values of change in arc tangent of the ratio of electric field and the phase retardation between two polarizations were obtained as functions of square of the Raman-Nath parameter. From intercepts of those values, the complex strain-optical parameters were determined. The frequency dependences of the complex strain-optical parameters at 40, 50 and 60 °C were obtained and compared with those calculated by using the data of using the reorientational relaxation frequency and the flow birefringence per unit strain rate. Although some discrepancies are found at 40 and 50 °C, the results indicate applicability the proposed method to determine the strainoptical coefficients above MHz range.

High-Frequency Rheo-Optical Spectroscopy by Ultrasonically Induced Light Diffraction

“…6) In this study, we improved that system to raise the upper frequency limit to 75 MHz. We also measured shear relaxation spectra to discuss viscoelastic behavior in comparison with complex strain-optical coefficient spectra.…”

“…We have reported complex strain-optical coefficient measurement of an isotropic-phase liquid crystal, 4-cyano-4 0 -pentylbiphenyl (5CB), in the frequency range from 5 to 25 MHz, using ultrasonically induced light diffraction method. 6) In this study, we improved that system to raise the upper frequency limit to 75 MHz. We also measured shear relaxation spectra to discuss viscoelastic behavior in comparison with complex strain-optical coefficient spectra.…”

“…From and Á, we can obtain complex strain-optical coefficient O Ã ¼ O 0 þ iO 00 in the same way as in our previous study. 6) Figure 1 shows a schematic illustration of improved measurement system. Improvement was carried out as follows.…”