Hydrophobic hydration and concentration fluctuations in aqueous solutions of urea derivatives. Evidence from dielectric and ultrasonic spectrometry

Abstract

At 25 degreesC the complex (electric) permittivity of aqueous solutions of n-butylurea and tetramethylurea has been measured as a function of frequency nu (1 MHz less than or equal tonuless than or equal to40 GHz) and solute concentration c 0.5 mol/lless than or equal tocless than or equal to1.26 mol/l). A suitable relaxation spectral function was fitted to the experimental data to yield various parameters, particularly the solute contribution to the static permittivity and the principal dielectric relaxation time of water. The former quantity has been evaluated to show equipartition of the structural isomers of n-BuU. The relaxation time is discussed in terms of local fluctuations in the solute concentration as deduced from ultrasonic spectra of the aqueous systems. (C) 2002 American Institute of Physics.