On the Discontinuity in the Temperature Coefficient of the Velocity of Ultrasonic Waves in Polymeric Materials

Abstract

It is proposed that the discontinuity is a manifestation of the sudden change in the expansion coefficient that occurs at the glass‐transition temperature. A comparison of volume‐temperature data with velocity‐temperature and velocity‐pressure data taken from the literature gives reasonably good agreement with this explanation. Further, the dependence of velocity on density is seen to be chiefly through the strong dependence of the modulus on density and to a lesser extent through the appearance of density explicitly in the equation that relates velocity to the density and modulus.