Ultrasonic Shear and Compressional Relaxation in Liquid Glycerol

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Abstract
Relaxation of the real parts of the shear and compressional moduli of liquid glycerol was investigated using ultrasonic pulse techniques. Measurements of the decibel loss/echo for a glycerol‐quartz interface were made at frequencies from 15 to 85 megacycles per second over the temperature range from +70°C to −40°C. Measurements of the velocity of longitudinal waves in glycerol were made at frequencies from 1 to 55 Mc per sec over the temperature range from +50° to −80°C. The limiting values of the real parts of the shear and compressional moduli are studied and compared over the temperature range. The behavior of the relaxational parts of the real parts of the shear and compressional moduli cannot be quantitatively explained by either classical or single relaxation time theory. A distribution of relaxation times is shown to be adequate to explain both the shear and compressional relaxations. The average compressional relaxation time is found to be equal to 0.81 times the average shear relaxation time.

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