title: How Is Diffusion of Neutral and Charged Tracers Related to the Structure and Dynamics of a Room-Temperature Ionic Liquid? Large Deviations from Stokes-Einstein Behavior Explained.
abstract: The deviations from Stokes-Einstein hydrodynamics of small solutes are more pronounced in ionic liquids than in conventional solvents (J. Phys. Chem. B 2013 117 (39), 11697). Small neutral solutes diffuse much faster than expected, whereas small charged solutes diffuse much slower. This article attempts to establish a link between the local friction experienced by tracer solutes and the polar/apolar structure of ionic liquids. We find that small neutral solutes probe locally "stiff" (mostly charged, high electrostriction) regions and locally "soft" (mostly apolar, low electrostriction) regions. These regions of high and low friction are associated with cage and jump regimes. Enhanced neutral tracer mobility in the low friction regions associated with the cationic apolar component has an important bearing on the large positive deviations from Stokes-Einstein behavior. In contrast, diminished charged tracer mobility involves long caging dynamics separated by jump events often triggered by the loss and recovery of counterions.
authors: †Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States.
authors: Juan C
authors: JC
authors: Araque
authors: †Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States.
authors: Sharad K
authors: SK
authors: Yadav
authors: ‡Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States.
authors: Michael
authors: M
authors: Shadeck
authors: ‡Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States.
authors: Mark
authors: M
authors: Maroncelli
authors: †Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States.
authors: Claudio J
authors: CJ
authors: Margulis