High-Resolution Ultrasonic Spectroscopy: Looking at the Interpolyelectrolyte Neutralization from a Different Perspective

In this study, the high-resolution ultrasonic spectroscopy (HR-US) technique was applied to examine interpolyelectrolyte neutralization. The mentioned method was tested on the example of complexation between poly(allylammonium) cations and poly(acrylate) anions in aqueous solutions at pH = 7. It was confirmed by HR-US that the type of titration (stepwise or abrupt), the direction of titration, and the type of background salt affect the outcome of interpolyelectrolyte neutralization. The obtained results were explained on the basis of ultrasonic velocity and attenuation changes in the context of suspension compressibility, a parameter that is extremely sensitive to molecular organization and intermolecular interactions. Moreover, the results of HR-US measurements proved to be consistent with previous results obtained by more traditional methods such as dynamic light scattering, microcalorimetry, and electrokinetics. This research demonstrates that HR-US is a convenient and reliable method that can be employed for the investigation of interpolyelectrolyte neutralization and polyelectrolyte-related processes.