Water dynamics in dilute aqueous solutions of small apolar solutes by quasi-elastic neutron scattering

Tert-butyl alcohol (TBA) and trimethyl-amino-N-oxide (TMAO) are organic molecules with the same hydrophobic moiety and a different polar group. They can be used as model systems to study how hydrophobic molecules in aqueous solutions affect water dynamics. We report here first results of a quasi-elastic neutron-scattering experiment on H2O/TBA and H2O/TMAO mixtures, varying the solute concentration in the range 0-2 mol %. In both systems, the effect on the microdiffusivity parameters upon increasing the solute concentration is similar to that observed in pure water on decreasing the temperature: the water dynamics slows down. In the concentration range analysed, no marked differences have been observed between the two systems.