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

Abstract

Theoretical expressions for the ultrasonically induced birefringence of liquids are obtained in the frame work of de Gennes’ phenomenological theory. The intensity and frequency dependence of ultrasonically induced birefringence in the isotropic phase of p-n-pentyl p′-cyanobiphenyl (5CB) was measured in order to examine the usefulness of birefringence measurements for investigating dynamical properties liquids. The observed birefringence was proportional to the square root of ultrasonic intensity. The birefringence divided by the square root of ultrasonic intensity increases with increasing frequency and appears to saturate when the ultrasonic frequency approaches the relaxation frequency of molecular reorientation. The observed values of birefringence were reproduced satisfactorily by the expression derived in this paper.

Long-range orientation correlation in water

“…Molecular alignment by molecular rotation-translation coupling is observed both in flow birefringence and the central dip in the depolarized light scattering spectrum for shear waves, and in ultrasonic induced birefringence for longitudinal waves. [13][14][15][16][17] Those experiments are all governed by the same dimensionless rotation-translation coupling parameter 0 ≤ R RT ≤ 1. 13 The experimentally observed value for this parameter is nearly temperature independent and falls in the range R RT = 0.4 ± 0.2 for a variety of liquids.…”

Linear and Nonlinear Ultrasonically Induced Birefringence in Polymer Solutions

“…The relaxation time τ is give as τ = 1/(4µD). This equation is similar to that for neat liquids; 8,11,12) the induced birefringence is proportional to the square root of ultrasonic intensity. Badoz 17) modified Peterlin's theory, taking into account the internal electric field using a different model for flexible molecules suggested by Cerf 22,23) in his theory of flow birefringence.…”

“…One is the "nonbiased" technique 8) and the other is the "biased" technique. 3,5) Figure 1 shows a block diagram of the experimental system used in this study.…”

“…[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.…”

Direct Observation of Sinusoidal Ultrasonically Induced Birefringence in Liquid Crystal in the Isotropic Phase

“…The temperature dependence of the sinusoidal birefringence per unit of the ultrasonic amplitude was measured and the compared to the theoretical prediction for sinusoidal birefringence based on de Gennes' phenomenological theory for the translational-reorientational coupling. 4,10,11) 2. Experimental Figure 1 schematically shows the experimental system designed for the direct observation of the sinusoidal birefringence induced by the ultrasonic wave.…”