Temperature dependent association and relaxation in monoalkyl ethers of ethylene glycol and of diethylene glycol in dilute solutions of benzene from static and complex microwave dielectric measurements

The dielectric properties of two homologous series of ethylene oxide conden sation products i.e. monoalkyl ethers of ethylene glycol and monoalkyl ethe rs of diethylene glycol have been investigated in dilute solutions of benze ne at 20 degrees C, 35 degrees C and 45 degrees C to clarify the structural dynamics of these molecules. The low frequency molecular dynamics of these molecules have been studied by evaluating the Kirkwood correlation factor, molar polarization and dipole moment using the 1 MHz static dielectric con stant and the dielectric constant of induced polarization. The observed val ues of the Kirkwood correlation factor significantly deviated from unity co nfirm the intermolecular association in these molecules in dilute solutions . The high frequency molecular dynamics were examined using 9.83 GHz microw ave dielectric relaxation times corresponding to overall rotation and group rotations. These relaxation times have been discussed in terms of the effe ct of chain length, viscosity, size of alkoxy groups and molecular associat ion with temperature variation. A switch-over type of mechanism is also dis cussed in these associating molecules due to breaking and reforming of hydr ogen bonds, considering the temperature dependent dielectric, parameters. T he dynamics of these molecules have been compared to the rather similar beh aviour of small chain and long chain associating molecules. (C) 1999 Elsevi er Science B.V. All rights reserved.