Birefringence induced in liquids and solutions by ultrasonic waves

On the frequency dependence of ultrasonically induced birefringence in isotropic phase of liquid crystal: 5CB (p-n-pentyl p′-cyanobiphenyl)

“…The reorientational order produced is not uniform but propagates as waves and the induced birefringence should be proportional to the ultrasonic amplitude, that is, the square root of the ultrasonic intensity. 1,[6][7][8] In the neat liquids, we cannot obtain the transient decay curve after rapid cessation of ultrasonic irradiation. If the relaxation frequency for reorientational motion is close to the applied ultrasound frequency, the birefringence per amplitude of the applied ultrasonic wave should be affected by the reorientational relaxation processes of the molecules.…”

“…[1][2][3][4][5][6][7][8] For large particles of anisotropic shape such as rodlike and planar colloidal particles, ultrasonic radiation pressure produces a stationary torque on the particles and induces reorientational order as a whole, because the orientational relaxation frequency of particles is much smaller than that of ultrasound frequency. In this case, the induced birefringence is proportional to the ultrasonic intensity.…”

“…We also compare our results with the earlier theories. 1,[23][24][25] The isotropic phase of liquid crystals is most appropriate to examine the expression obtained here, because the relaxation frequencies of the orientational motions are the same order of magnitude as the ultrasonic frequencies usually used for ultrasonic relaxation studies. 26 Besides, the flow birefringence for isotropic phase of liquid crystal, 5CB, has been already reported by Martinoty et al 7 The values of the flow birefringence and the relaxation frequencies are required to reproduce the frequency dependence of the ultrasonically induced birefringence.…”

“…[1][2][3][4][5] The dynamical properties of large particles can be investigated by following the decay of the birefringence after rapid cessation of ultrasonic irradiation. [1][2][3][4][5] For neat liquids, however, a sinusoidal velocity gradient can directly produce sinusoidal orientational order. The reorientational order produced is not uniform but propagates as waves and the induced birefringence should be proportional to the ultrasonic amplitude, that is, the square root of the ultrasonic intensity.…”

Linear and Nonlinear Ultrasonically Induced Birefringence in Polymer Solutions

“…[1][2][3][4][5][6][7][8][9][10] The reorientation of molecules or particles under ultrasound occurs by two mechanisms. One is due to the sinusoidal velocity gradient, 1,2,[7][8][9][9][10][11][12] and the other is due to the radiation pressure of ultrasound. 1-6, 11, 13, 14) For neat liquids, molecular reorientation can follow the sinusoidal velocity gradient produced by ultrasound.…”