Sound propagation in moderately supercooled liquids. A comparison with water

Ultrasonic investigations in benzophenone, diphenylamine, and a solution of these two liquids on going from the stable down to the supercooled region confirm the peculiar behavior of sound propagation previously found in other systems. A comparison with ultrasonic absorption and velocity data in supercooled water shows that both kinds of systems exhibit similar anomalies. This suggests that the same physical interpretation may explain such findings. The large absorption in the supercooled region is attributed to structural relaxation processes whose characteristic times largely increase in the metastable state. An evaluation of such times in water indicates that dispersion in both absorption and velocity would not be detectable down to ∼−20 °C. Such findings agree with recent experimental observations and eliminates some inconsistencies present in the existing experimental data. A comparison of the structural relaxation times with those found in other transport properties in supercooled water shows a close connection with a nearly equal activation energy. Sound velocity anomalies at lower temperatures are explained on the grounds of ’’heterophase’’ contributions.