Ultrasonic Relaxation in Normal Propyl Alcohol

Abstract

Ultrasonic relaxation has been investigated in normal propyl alcohol using pulse techniques. Measurements of velocity and absorption were made at frequencies from 1 to 82 megacylces and over a temperature range 0 to −155°C. The data could be explained by assuming a distribution of relaxation times, and it was suggested that the distribution of relaxation times is but a reflection of the distribution of activation energies for the elementary molecular processes involved. A theory based on the assumption of a uniform distribution of activation energies for compressional processes and a single relaxation time for the shear process was presented. The agreement between the values calculated from this theory and the experimental data is good except at very high viscosities. The compressional viscosity calculated from the theory was found to be nearly equal to the shear viscosity except at very high viscosities. This is in agreement with the compressional viscosity calculated from the ``excess'' absorption in the nondispersion region.