Impact of Hydrogen Bonding on the Dynamics and Structure of Protic Ionic Liquid/Water Binary Mixtures
29 Aug 2017-Journal of Physical Chemistry B (American Chemical Society)-Vol. 121, Iss: 36, pp 8564-8576
TL;DR: The orientational dynamics and microscopic liquid structure of a protic ionic liquid, 1-ethylimidazolium bis(trifluoromethylsulfonyl)imide (EhimNTf2), and its aprotic analogue, 1
Abstract: The orientational dynamics and microscopic liquid structure of a protic ionic liquid, 1-ethylimidazolium bis(trifluoromethylsulfonyl)imide (EhimNTf2), and its aprotic analogue, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimNTf2), were studied at various water concentrations using optical heterodyne-detected optical Kerr effect (OHD-OKE) spectroscopy, linear infrared spectroscopy, and atomistic simulations. The OHD-OKE experiments essentially measure the orientational relaxation of the Ehim+ and Emim+ cations. The experiments and simulations show a significant dynamical and structural change in EhimNTf2 between the 2:1 ion pair:water and the 1:1 ion pair:water concentrations. The OHD-OKE data show that EmimNTf2/water mixtures exhibit hydrodynamic behavior at all water concentrations up to saturation. In contrast, EhimNTf2/water mixtures deviate from hydrodynamic behavior at water concentrations above 2:1. At the 1:1 concentration, the orientational randomization of the Ehim+ cation is ...
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TL;DR: This review comprehensively trace recent advances in understanding delicate interplay of strong and weak interactions that underpin their complex phase behaviors with a particular emphasis on understanding heterogeneous microstructures and dynamics of ILs in bulk liquids, in mixtures with cosolvents, and in interfacial regions.
Abstract: Ionic liquids (ILs) are a special category of molten salts solely composed of ions with varied molecular symmetry and charge delocalization. The versatility in combining varied cation-anion moieties and in functionalizing ions with different atoms and molecular groups contributes to their peculiar interactions ranging from weak isotropic associations to strong, specific, and anisotropic forces. A delicate interplay among intra- and intermolecular interactions facilitates the formation of heterogeneous microstructures and liquid morphologies, which further contributes to their striking dynamical properties. Microstructural and dynamical heterogeneities of ILs lead to their multifaceted properties described by an inherent designer feature, which makes ILs important candidates for novel solvents, electrolytes, and functional materials in academia and industrial applications. Due to a massive number of combinations of ion pairs with ion species having distinct molecular structures and IL mixtures containing varied molecular solvents, a comprehensive understanding of their hierarchical structural and dynamical quantities is of great significance for a rational selection of ILs with appropriate properties and thereafter advancing their macroscopic functionalities in applications. In this review, we comprehensively trace recent advances in understanding delicate interplay of strong and weak interactions that underpin their complex phase behaviors with a particular emphasis on understanding heterogeneous microstructures and dynamics of ILs in bulk liquids, in mixtures with cosolvents, and in interfacial regions.
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TL;DR: In this paper , a review summarizes the recent development of ionic liquids and ionic liquid-based electrolytes in terms of physiochemical properties, interphase formation ability, and electrochemical performance in lithium-ion batteries.
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TL;DR: Computational and computational studies indicate that microscopic intraionic interactions within CAGE are not substantially changed until the water content exceeds 0.65 mole fraction, and this suggests that CAGE could be used without predrying in most applications and can be diluted to induce the organization of the anions where desired.
Abstract: Choline and geranic acid (CAGE)-based ionic liquids have been recently developed for applications in drug delivery. Understanding the microscopic structures of CAGE in the presence of water is critical for its continued use in biomedical applications as it will undoubtedly come into contact with water in physiological fluids. Water can drastically impact the physicochemical properties of the ionic liquids, including CAGE. Computational and experimental characterization, namely viscosity, conductivity, and self-diffusion coefficient, were employed here to understand the properties of equimolar CAGE (1:1 choline/geranic acid) in the presence of varying amounts of water. It was found that under stored conditions, 1:1 CAGE contained up to 0.20 mole fraction water. Experimental and computational studies indicate that microscopic intraionic interactions within CAGE are not substantially changed until the water content exceeds 0.65 mole fraction. At this point, we theorize that the geranate ions undergo reorganization to minimize contact between the hydrophobic tails and the water molecules. This is evidenced by the plateau in viscosity at this mole fraction, and the increased interactions between the tails of the anions. This suggests that CAGE could be used without predrying in most applications and can be diluted to induce the organization of the anions where desired.
37 citations
TL;DR: Molecular dynamics simulations of ionic liquid (IL)-water mixtures used to investigate the effects of water addition provide various hydrophobicity/hydrophilicity of anions and hydrophobic features in the water content dependences of the diffusion constant.
Abstract: We performed molecular dynamics (MD) simulations of ionic liquid (IL)–water mixtures to investigate the effects of water addition. The IL cation 1-butyl-3-methylimidazolium ([C4mim]) and the four anions, nitrate (NO3), tetrafluoroborate (BF4), hexafluorophosphate (PF6), and bis(trifluoromethanesulfonyl)imide (NTf2), were used to examine the effects of differences in hydrophobicity and anion size. The radial distribution functions of water–water have two different water content dependences. In NO3 and BF4 systems, the effect of water–anion–water structures connected by hydrogen bonds due to the strong interaction of anion–water is large. The growth of water clusters changes the peak heights of the radial distribution functions in PF6 and NTf2 systems. The increase in the diffusion constant is small in the NO3 system but is not small in the other systems. The relaxation time of the anion–water hydrogen bonds in the NO3 system is much longer than those in the other systems. It is the reason for the low water...
32 citations
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