Effect of the Chain Length on the Inter- and Intramolecular Dynamics of Liquid Oligo(ethylene glycol)s

Abstract

Precise complex permittivity spectra over the frequency range 0.15 GHz ≤ ν ≤ 89 GHz are reported for monodisperse (EGn, 1 ≤ n ≤ 6) and polydisperse (PEG174, PEG300, PEG400) oligo(ethylene glycol)s at 25 °C. Up to ∼20 GHz, the relaxation behavior of all samples can be reasonably described with empirical functions that reflect a broad and asym. relaxation time distribution, like the Havriliak-Negami function. However, these functions deviate systematically at higher frequencies and do not allow one to rationalize the concn. dependence of the spectra on diln. in dichloromethane or when going from the diol to the corresponding di-Me ether. A coherent description can be achieved by using a superposition of Debye-type relaxation processes. This approach allows the sepn. of end-group effects connected with the relaxation of the hydrogen bond network from intramol. dipole relaxation processes caused by the reorientation of chain segments.