Ultrasonic Vibration Potentials in Polyelectrolytes

Abstract

When ultrasonic waves are propagated through aqueous solutions of polyelectrolytes, alternating potential differences are generated between points separated by a phase distance other than an integral multiple of the wavelength. This effect is somewhat similar to the ionic and colloidal vibration potentials reported previously [J. Acoust. Soc. Am. 25, 456 (1953)] and occurs because of differences in the dynamic reactions of the large polymeric ions, the simple ions, and the solvent molecules to the material waves. In the absence of sound waves, the charge distribution associated with each polyelectrolyte particle is statistically symmetrical. In the sound field, each polyelectrolyte particle and its ionic atmosphere act as an oscillating dipole. This effect has been examined in polyacrylic acid solutions as a function of concentration and percent neutralization of the polyelectrolyte. Pulse-modulated ultrasonic waves have been used for the measurements at frequencies from 200 to 1000 kc/sec. The observed amplitude is in the range 10−5 to 10−4 v per unit velocity amplitude (cm/sec). This effect is expected to prove useful in establishing the state of coiling of polyelectrolytes. [This research has been supported by the Office of Naval Research under Contract No. 1439(04).]