Microwave Dielectric Behaviour of 1,2-Propanediol-water Mixture Studied Using Time Domain Reflectometry Technique Satyajit Chavan, a, * Ashok Kumbharkhane a and Suresh Mehrotra b a School of Physical Sciences, Swami Ramanand Teerth Marathwada University, Nanded 431 606, (MS) India b Department of Computer Science & Information Technology, Dr. B.A. Marathwada University, Aurangabad 431 004, (MS) India The dielectric behaviour of 1,2-propanediol was investigated to understand the effect of the hydroxyl group on the dielectric parameters. The measurement of permittivity e¢ and e² of 1,2-propanediol was car- ried out in the frequency range 10 MHz to 20 GHz at 25 °C temperature. Static permittivity and dielectric relaxation time are extracted from a 1,2-propanediol-water mixture using the bilinear calibration method and non-linear least squares fit method. Calculated Kirkwood correlation factor contains information re- garding solute-solvent interaction. The hydrogen bonded model suggested by Luzar is applied to deter- mine the molecular parameters. The excess dielectric parameters and Bruggeman factor show the system- atic change in the dielectric parameter of the system with change in concentration. Keywords: Dielectric constant; Mixture; Time domain reflectometry. INTRODUCTION Over the last few years many experimental results concerning the dielectric behaviour of binary solutions have been published. 1-4 Dielectric spectroscopy has been extensively used for many years to study interactions in hy- drogen bonded liquid systems such as alcohols. 5-9 Investi- gations of dihydric alcohols or diols are of interest as diols resemble water in their dielectric behaviour. 8-10 Recently, depolarized light scattering spectroscopy 11 has been em- ployed to study the molecular dynamics of glass forming H-bonded dihydric liquids, and they have -OH groups in the segments of their molecular chain. Water is in many aspects a remarkable liquid. There is general consensus that the anomalous properties of liquids water to a great extent are caused by the presence of hydro- gen bonds. 12 A water molecule can form up to four hydro- gen bonds with other water molecules thereby creating the possibility for a local tetrahedral structure around the mole- cule. The measurement of dielectric relaxation is a good tool to study molecular interactions in hydrogen bonded liquids such as water and diols, because each molecule has an electric dipole moment. To gain some insight into the na- ture of molecular interactions between the associating mol- ecules, a dielectric study of a 1,2-propanediol-water sys- tem should be helpful. Furthermore, the environment of water solvent can be modified by the 1,2-propanediol mol- ecules because of strong interactions between the hydroxyl groups of diol and water. Extensive dielectric relaxation studies were carried out for different concentrations of a diol-water 13 system to understand the solute-solvent inter- action and dynamics behaviour of water. Values of the static dielectrics of ethylene glycol (EG) and diethylene gly- col (DEG) show there is a decrease in the static dielectric constant with increase in chain length due to the increase in the number of carbon atoms. No attempt seems to have been made to study the dielectric behaviour of 1,2-propanediol- water in the microwave region. So the present work is totally based on a 1,2-propanediol-water mixture to verify the di- electric properties of the mixture at the frequency of 20 GHz. EG [OHCH 2 CH 2 OH] and DEG [CH 3 CH(OH)CH 2 OH] have two and three carbon atoms, respectively, whereas 1,2-pro- panediol [OHCH 2 CH 2 OCH 2 CH 2 OH] has four carbon at- oms. Interest in 1,2-propanediol liquid is also due to its having one carbon atom extra compared to EG and DEG. Materials 1,2-Propanediol was used from S D Fine Chemical, Limited; water was used after double glass distillation and Journal of the Chinese Chemical Society, 2007, 54, 1457-1462 1457 * Corresponding author. E-mail: satyajit@iucaa.ernet.in