Propagation of Transverse Elastic Waves in Polyisobutylene under Various Pressures

Abstract

The velocity and the absorption coefficient of 2-Mc transverse elastic waves in polyisobutylene (molecular weight, 1.35 × 106) have been measured at pressures up to 1400 atm for temperatures of 10°C and 20°C. Pulsed signals are conducted into and out of a thin sample via Y-cut cylinders of crystalline quartz to which the sample is bonded. The object of the measurements is to determine δT/δP for constant behavior—in this case, for constant dynamic mechanical properties in shear. Closely similar derivatives are already known on the basis of (1) the behavior of the absorption maximum for bulk waves; (2) dynamic mechanical properties in compression; (3) hydrogen nuclear magnetic resonance absorption line width; (4) calculations based on a theory due to F. Bueche. All of these results, as well as the present measurement, yield values in the neighborhood of 0.02 C°/atm for δT/δP. (Assisted by the Office of Naval Research.)