Hydrogen bonding and chain conformational isomerization of alcohols probed by ultrasonic absorption and shear impedance spectrometry

Abstract

The acoustical absorption spectra between 300 kHz and 3 GHz and the complex shear viscosity spectra between 6 and 120 MHz for some monohydric alcohols are reported. The acoustical spectra exhibit two relaxation regions, one located at frequencies around some hundred MHz and the other one around some GHz. The shear viscosity spectra reveal a relaxation process in conformity with the low-frequency acoustical relaxation. This relaxation is assigned to fluctuations in the structure of hydrogen bonded alcohol clusters. The high-frequency acoustical relaxation is discussed in terms of a damped torsional oscillator model of allkyl chain isomerization, corresponding with the rotational isomerization of n-alkanes. The high frequency (>5 GHz) shear viscosity of the alcohols is estimated and found in the same order (1 mPa s) as that for n-alkanes.