Abstract
Room-temperature ionic liquids are promising candidates for applications ranging from electrolytes for energy storage devices to lubricants for food and cellulose processing to compounds for pharmaceutics, biotransformation, and biopreservation. Due to the ion complexity, many room-temperature ionic liquids readily form amorphous phases upon cooling, even at modest rates. Here, we investigate two commonly studied imidazolium-based room-temperature ionic liquids, 1-ethyl-3-methylimidazolium tetrafluoroborate and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, as well as their mixtures, to demonstrate how the complex interplay between the crystalline and amorphous phases is affected by the processing conditions, such as thermal history, liquid mixing, and applied pressure. We show that quantum tunneling in the cation methyl groups, measured by high-resolution inelastic neutron scattering, can be used to probe the order-disorder in room-temperature ionic liquids (crystalline vs amorphous state) that develops as a result of variable processing conditions.
Highlights
Room-temperature ionic liquids (RTILs) are tremendously versatile solvents with a broadly recognized potential for application in numerous fields.[1,2,3,4,5,6,7,8,9,10] More recently, RTILs have attracted much attention for their remarkable affinity for various biomolecules;[11–15] especially in pharmacology, biomedicine, and bionanotechnology applications, where the behavior of RTILs at low temperatures is of importance
We show that quantum tunneling in the cation methyl groups, measured by high-resolution inelastic neutron scattering, can be used to probe the order-disorder in room-temperature ionic liquids that develops as a result of variable processing conditions
The samples of two common imidazolium-based room-temperature ionic liquids (RTILs), EmimBF4 and EmimTFSI, whose mixtures have been previously investigated for energy storage applications,[20,34] were subjected to various treatments to make them either crystalline or amorphous at cryogenic temperatures
Summary
Room-temperature ionic liquids (RTILs) are tremendously versatile solvents with a broadly recognized potential for application in numerous fields.[1,2,3,4,5,6,7,8,9,10] More recently, RTILs have attracted much attention for their remarkable affinity for various biomolecules;[11–15] especially in pharmacology, biomedicine, and bionanotechnology applications, where the behavior of RTILs at low temperatures is of importance This is because, for biocompatibility and biopreservation, the order or disorder in the structure of the host at low temperature may affect the packing and, the thermal meansquared displacements of the guest molecules. The purpose of the current neutron scattering work, for which we chose two extensively studied[20] imidazolium-based RTILs (Fig. 1), 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF4) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimTFSI), is to demonstrate how high energy-resolution inelastic neutron scattering (INS) can measure quantum methyl tunneling in RTIL cations to probe the order-disorder (crystalline vs amorphous state) that may develop in RTILs under different conditions.
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