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

Precise complex permittivity spectra over the frequency range 0.15 GHz </= nu </= 89 GHz are reported for monodisperse (EGn, 1 </= n </= 6) and polydisperse (PEG174, PEG300, PEG400) oligo(ethylene glycol)s at 25 degrees C. Up to about 20 GHz, the relaxation behavior of all samples can be reasonably described with empirical functions that reflect a broad and asymmetric relaxation time distribution, like the Havriliak-Negami function. However, these functions deviate systematically at higher frequencies and do not allow one to rationalize the concentration dependence of the spectra on dilution in dichloromethane or when going from the diol to the corresponding dimethyl ether. It is shown that a coherent description can be achieved by using a superposition of Debye-type relaxation processes. This approach allows the separation of end-group effects connected with the relaxation of the hydrogen bond network from intramolecular dipole relaxation processes caused by the reorientation of chain segments.