Sound absorption and concentration fluctuations in water–propanol mixtures

The excess ultrasonic sound absorption in 1‐propanol water mixtures has been measured from 45 kHz to 474 MHz and is shown to result from a coupling of the sound wave with the long‐wavelength spectrum of the composition fluctuations. The results are shown to be in agreement with the fluctuation theories of Fixman, Romanov and Solovyev, and Kawasaki and the more recent theories of Kroll and Ruhland, and Bhattacharjee and Ferrell. It is further suggested that the large absorption observed in alcohol–water mixtures may be due to the presence of large associated groups, or clusters.