Longitudinal acoustic relaxation of highly viscous liquids around room temperature

Abstract

The sound velocities of highly viscous liquids, tri-o-tolylphosphate, di-isobutylphthalate and triacetin, were measured in the frequency range 100–400 MHz around room temperature by the high-resolution Bragg reflection method. The velocity dispersion was observed in the frequency range. Taking account of the longitudinal modulus in the GHz region obtained in a previous paper (Hashitani et al. Jpn J. Appl. Phys., 1988, suppl. 27-1, 41), the relaxation curves of longitudinal modulus in the frequency range from MHz to GHz frequencies could be reproduced by the double relaxation equation. Of the two relaxational processes, contribution of the faster one increased rapidly with temperature. The two relaxation processes observed have been discussed within the framework of the linear viscoelastic theory.