Comparison Between Mechanical Relaxations Associated with Volume and shear Deformations in Styrene-Butadiene Rubber

Velocity and attenuation of longitudinal ultrasonic waves in styrene-butadiene rubber are measured in the temperature from 0° to 50°C at frequencies 1, 3 and 5Mc/s and real and imaginary parts of longitudinal wave modulus ( K +4 G /3) are calculated. Comparing the results with the data of bulk moduls ( K ) previously obtained for the same sample by the suspension method (J. Phys. Soc. Japan 15 (1960) 2324), we find that relaxation times, their temperature dependence and the spectra of distribution of relaxation times are quite similar for volume and shear deformationns. This may be a consequence of the fact that both the deformations are associated with the same molecular motions. Shear modulus ( G ) is obtained for comparison at a single frequency 1 Mc/s in the temperature between 0° and 20°C.