Sound attenuation in the critical region of the ionic binary mixture ethylammonium nitrate/n-octanol

Abstract

Ultrasonic attenuation spectra (100 kHz<f<4 MHz) of the ionic mixture ethylammonium nitrate/n-octanol of critical composition and also of the ethylammonium nitrate itself (100 kHz <f< 400 MHz) are discussed at different temperatures. The measured spectra are evaluated in terms of the Bhattacharjee–Ferrell dynamic scaling theory. Using literature data for the amplitude of the fluctuation correlation length, the background and critical part of the heat capacity, the sonic attenuation spectrum as predicted by the Bhattacharjee-Ferrell model has been calculated for the critical mixture at the critical temperature. Again following this theoretical model, the contribution due to concentration fluctuations has been subtracted from the measured spectra at the temperatures of measurement and also subtracted has been the high-frequency asymptotic background contribution. The measured data are consistent with the Bhattacharjee–Ferrell theory of critical concentration fluctuations but show an additional frequency dependence. [Work supported by the Volkswagen-Stiftung, Hannover, Germany.]