Structure and nanostructure in ionic liquids.

In recent years, the designer nature of ionic liquids (ILs) has driven their exploration and exploitation in countless fields among the physical and chemical sciences. A fair measure of the tremendous attention placed on these fluids has been attributed to their inherent designer nature. And yet, there are relatively few examples of reviews that emphasize this vital aspect in an exhaustive or meaningful way. In this critical review, we systematically survey the physicochemical properties of the collective library of ether- and alcohol-functionalized ILs, highlighting the impact of ionic structure on features such as viscosity, phase behavior/transitions, density, thermostability, electrochemical properties, and polarity (e.g. hydrophilicity, hydrogen bonding capability). In the latter portions of this review, we emphasize the attractive applications of these functionalized ILs across a range of disciplines, including their use as electrolytes or functional fluids for electrochemistry, extractions, biphasic systems, gas separations, carbon capture, carbohydrate dissolution (particularly, the (ligno)celluloses), polymer chemistry, antimicrobial and antielectrostatic agents, organic synthesis, biomolecular stabilization and activation, and nanoscience. Finally, this review discusses anion-functionalized ILs, including sulfur- and oxygen-functionalized analogs, as well as choline-based deep eutectic solvents (DESs), an emerging class of fluids which can be sensibly categorized as semi-molecular cousins to the IL. Finally, the toxicity and biodegradability of ether- and alcohol-functionalized ILs are discussed and cautiously evaluated in light of recent reports. By carefully summarizing literature examples on the properties and applications of oxy-functional designer ILs up till now, it is our intent that this review offers a barometer for gauging future advances in the field as well as a trigger to spur further contemplation of these seemingly inexhaustible and—relative to their potential—virtually untouched fluids. It is abundantly clear that these remarkable fluidic materials are here to stay, just as certain design rules are slowly beginning to emerge. However, in fairness, serendipity also still plays an undeniable role, highlighting the need for both expanded in silico studies and a beacon to attract bright, young researchers to the field (406 references).

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Ether- and Alcohol-Functionalized Task-Specific Ionic Liquids: Attractive Properties and Applications

Some of the most active scientific research fronts of the past decade are centered on ionic liquids These fluids present characteristic surface behavior and distinctive trends of their surface tension versus temperature One way to explore and understand their unique nature is to study their surface properties This critical review analyses most of the surface tension data reported between 2001 and 2010 (187 references)

Surface tension of ionic liquids and ionic liquid solutions

The solubilities and diffusion coefficients of hydrogen sulfide and carbon dioxide gases in the ionic liquid (IL) 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate ([hemim][BF4]), at temperatures ranging from (303.15 to 353.15) K and pressures up to 1.1 MPa, were determined. The solubility data were correlated using the Krichevsky−Kasarnovsky equation, and Henry’s law constants at different temperatures were obtained. From the solubility data, the partial molar thermodynamic functions of solution such as Gibbs energy, enthalpy, and entropy were calculated. The diffusion coefficients were obtained for H2S and CO2 using a semi-infinite volume approach, and a correlation equation with temperature is presented for each gas. A comparison showed that the solubility of H2S was about three times its magnitude, and its diffusion coefficient is of the same order of magnitude as that of CO2 in the IL studied in this work.

Solubility and Diffusion of H2S and CO2 in the Ionic Liquid 1-(2-Hydroxyethyl)-3-methylimidazolium Tetrafluoroborate

Molecular dynamics simulations of imidazolium-based ionic liquid/water mixtures: Alkyl side chain length and anion effects

Room-temperature ionic liquids based on the imidazolium cation are presently widely studied, but more data on important properties such as viscosity and surface tension are required. In this work, two imidazolium-based ionic liquids, 1-ethanol-3-methylimidazolium tetrafluoroborate [C2OHMIM][BF4] and 1-methyl-3-octylimidazolium tetrafluoroborate [OMIM][BF4], were investigated. The former is a member of a new series that contains the alcohol (CH2)2OH as a functional group. The latter, already studied by several authors, has a long side chain in the imidazolium ring that is responsible for its surfactant properties. The surface tension was determined using the pendant drop technique in a wide temperature range, (298 to 470) K, which has never been explored before with ILs. The viscosity was measured using a new technique (a quartz crystal microbalance) between (288 and 328) K. The surface tension and the viscosity of [C2OHMIM][BF4] are unexpectedly high when compared with those of [OMIM][BF4]. The experiment...

Viscosity and Surface Tension of 1-Ethanol-3-methylimidazolium Tetrafluoroborate and 1-Methyl-3-octylimidazolium Tetrafluoroborate over a Wide Temperature Range

The uptake of water vapor by ionic liquids (ILs) has been studied by various research groups, but there is little knowledge on how liquid confinement affects the process of moisture absorption. In this work, several imidazolium-based ILs deposited on quartz crystals were used as water vapor sensors in a high sensitivity quartz-crystal microbalance with dissipation. The process of water vapor absorption by the IL films was interpreted, taking into account the changes of the different harmonics of the fundamental frequency. For the most viscous ILs, such as [C2OHmim][BF4] and [C6mim][OAc], the decrease in viscosity was the dominant effect, while for the others, [C8mim][BF4], [C2mim][OAc], and [C4mim][OAc], the mass loading effect predominated. However, there are differences within the latter set: a gradual water adsorption and diffusion was observed in [C2mim][OAc] and [C4mim][OAc] films; in contrast, a discontinuity seems to have occurred between the formation of a water film on top of the [C8mim][BF4] fil...

José L. Mata

Papers

Viscosity and Surface Tension of 1-Ethanol-3-methylimidazolium Tetrafluoroborate and 1-Methyl-3-octylimidazolium Tetrafluoroborate over a Wide Temperature Range

Moisture Absorption in Ionic Liquid Films