Ultrasonic velocity and adiabatic compressibility in polyelectrolyte solutions

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Abstract
Ultrasonic velocities in poly(potassium methyl acrylate) solutions were measured at various concentrations. The ultrasonic frequency was (453.8 ± 0.1) kcycles/sec. The ultrasonic interferometer method was used to measure the sound velocity, the relative error of the measurement being kept within 0.1%. Moreover, the temperature variation of the sound velocity in these solutions in the dilute state was measured. While measuring the density, the adiabatic compressibilities at various conditions were estimated. It was found that both the increment of the ultrasonic velocity per unit concentration and the decrement of the adiabatic compressibility per unit concentration showed sharp maxima, at some very dilute concentration, in the case of a pure water solvent, and that these maxima disappeared when the solvent was changed from water to KCI solution. A plot of the ratio of the compressibility for solutions with pure water as solvent, to that for additions with KCI solution as solvent vs. temperature showed an inflection at a given temperature and thereafter leveled off at higher temperatures. The concentration change and temperature variation of the ultrasonic velocity and of the adiabatic conpressibility are qualitatively explained on the basis of Oosawa's theory of polyelectrolyte, solutions.