Influence of urea on hydrophobic phenomena in aqueous solutions of alcohols

Self-diffusion coefficients of tert-butanol and n-propanol have been measured in water-rich regions of solutions containing urea at 25°C. Hydrodynamic radii of both alcohols have been calculated for varying concentrations of alcohol and urea. Hydrophobic hydration causes the formation of stable molecular aggregates. These aggregates have been observed below a certain alcohol concentration, the critical clathrate concentration. The addition of urea does not influence the critical clathrate concentration of tert-butanol, but in solutions of n-propanol this point is shifted to higher alcohol concentration.