Macroscopicand Microscopic Study of 1-Ethyl-3-methyl-imidazoliumAcetate–DMSO Mixtures.

Macroscopic (steady-state viscosity,density) and microscopic (NMRchemical shifts, 1H NMR relaxation times, and diffusion)properties of the 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc])−dimethylsulfoxide (DMSO) mixture were studied in detail as a function of DMSOmolar fraction at various temperatures. Temperature dependencies wereused to calculate the activation energies. NMR results indicate thatat low molar fraction of DMSO (<0.4), it weakly associates withthe cation and in doing so disrupts the strong ion–ion associationthat exists in the pure ionic liquid. Stokes–Einstein equation,which linearly correlates the diffusion coefficient of a sphericalmolecule and macroscopic viscosity, was shown to work well for the[EMIM][OAc]–DMSO mixture. The influence of DMSO on the “anomalous”diffusion in [EMIM][OAc] (“quick” cation vs “slow”anion) was investigated; it was demonstrated that DMSO makes the cationdiffusion slower. All parameters studied showed relatively small deviationsfrom the ideal mixing rule behavior (from 20% to 50% difference betweenexperimental and theoretically predicted results), confirming weakinteractions between the components. [ABSTRACT FROM AUTHOR]