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Scholars Day: April 7, 2010

Is Water Tightly Bound to Ionic Liquids Up to Water Mole Fractions of 0.5?

The self diffusion of the cation, anion and water in the ionic liquid (IL)–water binary system containing the IL, 1-ethyl-3-methylimidazolium methanesulfonate ([emim][MeSO3]), has been studied using a nuclear magnetic resonance (NMR) technique known as diffusion ordered spectroscopy (DOSY). Self diffusion is the random translational Brownian motion of molecules in the absence of a concentration gradient or convection. Self diffusion coefficients were obtained for 10 mixtures with water mole fractions ranging from 0 (pure IL) to 0.9 at temperatures from 40 to 85 °C. All three species follow a continuous trend toward faster self diffusion with increasing water mole fraction. These results are contradictory to the belief that water is tightly bound to the IL with water mole fractions of up to 0.5 since no discontinuity is observed in the composition-dependent self diffusion coefficients. For each species, an Arrhenius analysis of the DOSY data was performed to determine the activation energy of translational motion. Interestingly, despite water diffusing about three times as fast as the IL, all three species have the same linear concentration-dependent activation energy.

Presenter: Anthony Zidell (Undergraduate Student)
Topic: Chemistry
Location: 28 Hartwell
Time: 10:45 am (Session II)