Differential Microscopic Mobility of Components within a Deep Eutectic Solvent.
From macroscopic measurements of deep eutectic solvents such as glyceline (1:2 molar ratio of choline chloride to glycerol), the long-range translational diffusion of the larger cation (choline) is known to be slower compared to that of the smaller hydrogen bond donor (glycerol). However, when the diffusion dynamics are analyzed on the subnanometer length scale, we find that the displacements associated with the localized diffusive motions are actually larger for choline. This counterintuitive diffusive behavior can be understood as follows. The localized diffusive motions confined in the transient cage of neighbor particles, which precede the cage-breaking long-range diffusion jumps, are more spatially constrained for glycerol than for choline because of the stronger hydrogen bonds the former makes with chloride anions. The implications of such differential localized mobility of the constituents should be especially important for applications where deep eutectic solvents are confined on the nanometer length scale and their long-range translational diffusion is strongly inhibited (e.g., within microporous media).
†Department of Chemistry, University of Missouri, Columbia, Missouri 65211, United States.
Durgesh V
DV
Wagle
†Department of Chemistry, University of Missouri, Columbia, Missouri 65211, United States.
Gary A
GA
Baker
‡Chemical and Engineering Materials Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.
Eugene
E
Mamontov
D002794:Choline / Q000737:chemistry; D004058:Diffusion; D005990:Glycerol / Q000737:chemistry; D006860:Hydrogen Bonding; D033363:Neutron Diffraction; D012997:Solvents / Q000737:chemistry*; D013696:Temperature
D012997:Solvents; D002794:Choline; D005990:Glycerol
ab initio calculations; deep eutectic solvent; diffusion; microscopic dynamics; quasielastic neutron scattering