Self-diffusion of molecules in aqueous solutions of tetramethylurea

Abstract

Solutions of tetramethylurea (I) in light and heavy water were studied by the proton spin echo method over a wide concentration range at different temperatures. The energies of self-diffusion activation for species in these systems were calculated. In the both systems, the lowest coefficient of self-diffusion and the highest energy of activation for all the temperatures studied (288 to 313 K) were found for its ∼20 mol % solution, which corresponds to a congruently melting compound in the solid phase and to maximum sound viscosity, density, and speed in aqueous solutions of tetramethylurea. The low-concentration range of compound I (from 1.2 to 5 mol %) proved to be featureless.