The propagation of sound in solutions of rubber and perspex

The absorption of ultrasonic waves in the frequency region 4…18 Mc/s was measured in several highly viscous solutions of rubber in benzene and perspex in pyridine. The absorption was less than in the pure solvents and there is evidence of relaxation. Measurements of the shear viscosity of a 10% rubber solution showed that the relaxation of the high flow viscosity was complete even at 50 kc/s. The absorption in the solutions must therefore be ascribed to the “bulk viscosity” of the solvents.