Sound absorption in water-methanol mixtures

Experimental results on the sound absorption of methanol-water mixtures are obtained by the pulse method in the range of 5 to about 700MHz and for a temperature of 5°C. Since a methanol molecule has a small hydrophobic radical, these systems are regarded as one of the simplest nonelectrolyte aqueous solutions and then the attenuation vs. frequency plot shows nearly a single relaxation process. The frequency dependence of sound absorption agrees well with the predictions of a concentration fluctuations theory by Endo who assumes two relaxation times. The reason for its small sound absorption in these systems was elucidated by the relaxation parameters which relates to a cut-off wave number for diffusion processes. A somewhat single relaxation behavior in the attenuation vs. frequency plots may be interpreted by a small value of cut-off wave number.