Reconsideration of Dielectric Relaxation of Aqueous Urea Solutions at Different Temperatures

Urea structures in aqueous urea solution (8 mol center dot L-1) were examined by dielectric relaxation spectroscopy (DRS) in the frequency range 500 MHz-50 GHz, from 20 to 80 A degrees C. The mixture behavior is described in terms of the Havriliak-Negami and two Debye type relaxation models whose evolution with temperature is analyzed. A distinct antiparallel arrangement of dipoles is obtained for urea in the aqueous solution, according to the Kirkwood correlation factor, calculated from the static permittivity. We have also analyzed enthalpy, entropy and the activation energy of molecular reorientation of aqueous urea solution, and analyzed the formation of dimers about urea and water using the density functional theory.