A comparative dielectric study of ethylene glycol and propylene glycol at different temperatures

The dielectric behaviour of ethylene glycol HO-[CH2CH2O]-H and propylene glycol HO-[CH(CH3)CH2O]-H were investigated to understand the effect of methyl side group on the dielectric parameters. The measurements of permittivity epsilon' and dielectric loss epsilon" of ethylene glycol and propylene glycol were carried out in the frequency range 200 MHz to 20 GHz, and 10 MHz to 4 GHz, respectively, at temperatures 25, 35, 45 and 55 degreesC. The dielectric dispersion of ethylene glycol follows the Cole-Cole behaviour whereas it obeys the simple Debye behaviour for propylene glycol. Static dielectric constant E., high frequency limiting dielectric constant F, relaxation time T. and thermo dynamical energy parameters (DeltaF(tau), DeltaH(tau) and AS(tau)) have been determined and discussed in terms of the effect of methyl side-group on molecular dynamics and intermolecular hydrogen bonds. Further the variation in dielectric parameters and molecular reorientation due to addition of either methyl side group or one ethylene oxide unit in the molecular structure has been explored by comparing the values of dielectric parameters of ethylene glycol with propylene glycol and diethylene glycol. (C) 2003 Elsevier B.V. All rights reserved.