Molecular relaxation dynamics of poly(propylene oxide glycol)-400–LiClO4 systems

Abstract

The dynamics of electrolytes dissolved in poly(propylene glycol)s are addressed by a combination of audiofrequency electrical conductivity measurements, IR spectra of the ₄ mode of ClO₄^–, microwave and far-IR dielectric spectra, radiofrequency and UHF ultrasonic absorption spectra, and visible refractivities at the sodium doublet wavelength. The combination of IR and conductivity results indicates that the majority of the electrolyte exists in these low relative permittivity media as a solvent-separated ion pair and not as free ions. The high viscosity of the medium causes an overlap of solvent and solute relaxations that requires a new analysis of the molecular dynamics. The dielectric and ultrasonic spectra correlate with a similar average relexation time but with different distribution parameters. This is ascribed to a similar polymer chain response to the two perturbing functions although with different cooperative character of the response. The dielectric modulus approach is also examined, revealing serious errors committed by the improper use of this method of analysis. The calculated molar refractions suggest that the anion is solvated by the end protons of the polymer chains.