The Rheological Study of Aqueous Solutions of Polyvinyl Alcohol at Ultrasonic Frequencies

Abstract

Abstract The ultrasonic velocity and the absorption have been measured over the 5–45 Mc./sec. frequency range for aqueous solutions of polyvinyl alcohol by means of an ultrasonic pulse technique which was similar in principle to that used by Pinkerton (Proc. Phys. Soc. B62, 286 (1949)). The temperature varied over the 3–70°C range. The velocity-versus-temperature curves have been found to be convex upwards, like that of pure water, but the peak shifts upwards and to the lower-temperature side with an increase in the concentration. The ultrasonic absorptions of aqueous solutions of partly-saponified polyvinyl alcohol have been found to be larger than those of perfectly-saponified alcohol at the same concentrations. Two relaxation mechanisms have been found for each sample. For the solutions of the perfectly-saponified sample, the first relaxation frequency, f1, is 35 Mc./sec. at 12°C, while the second relaxation frequency f2 is 40 Mc./sec. at 60°C, for example. On the other hand, these values have been found to be nearly equal for the solutions of the partly-saponified sample. The activation energy, ΔH2, obtained from the temperature dependence of f2 is about 4 kcal./mol., irrespective of the quantity of resuidal acetate groups, and the ΔH1 value forf1 is of the order of 10 kcal./mol.