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

Theoretical expressions for the ultrasonically induced birefringence of liq uids are obtained in the frame work of de Gennes' phenomenological theory. The intensity and frequency dependence of ultrasonically induced birefringe nce in the isotropic phase of p-n-pentyl p(')-cyanobiphenyl (5CB) was measu red in order to examine the usefulness of birefringence measurements for in vestigating dynamical properties liquids. The observed birefringence was pr oportional to the square root of ultrasonic intensity. The birefringence di vided 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. (C) 1999 American Institute of Physics. [S0021-9606(99)51728-5] .