Low frequency ultrasonic absorption in aqueous solutions from variable path through-transmission and pulse-echo measurements

Abstract

Acoustic absorption spectroscopy can characterize the complex intermolecular interactions within a solution. Currently, there are no wide-spread uses of the method and no commercially available systems exist that measure below 3 MHz. However, chemical processes have been shown to exist at as low as 300 kHz. Here we present measurements on aqueous solutions using two techniques: a variable path through-transmission method operating around 1 MHz and a pulse-echo method operating near 500 kHz. These methods overlap in frequency and their results agreed with each other. We also calibrated the setup using water and measured the sound speed in each sample. Finally, we present preliminary results for the absorption spectra of MgSO4 and other solvents. Accurate measurements of acoustic absorption at low ultrasonic frequencies could prove to be an important tool in the pharmaceutical and chemical manufacturing industries and can lead to better understanding of intermolecular processes in this frequency range.