Viscosity minima in binary mixtures of ionic liquids + molecular solvents

Abstract

The viscosity (η) of four binary mixtures (ionic liquids plus molecular solvents, ILs+MSs) was measured in the 283.15 < T/K < 363.15 temperature range. Different IL/MS combinations were selected in such a way that the corresponding η(T) functions exhibit crossover temperatures at which both pure components present identical viscosity values. Consequently, most of the obtained mixture isotherms, η(x), exhibit clear viscosity minima in the studied T-x range. The results are interpreted using auxiliary molecular dynamics (MD) simulation data in order to correlate the observed η(T,x) trends with the interactions in each mixture, including the balance between electrostatic forces and hydrogen bonding.

Anomalous and Not-So-Common Behavior in Common Ionic Liquids and Ionic Liquid-Containing Systems

“…However, the molecular reasoning behind this phenomenon is not very well understood (Srinivas et al, 2001; Abraham et al, 2007) and thereby it is hard to model the viscosity values of such mixtures using existing mixing rules and predictive methods (Qunfang and Yu-Chun, 1999). Such uncommon phenomenon has been shown for the first time in systems containing ionic liquids (ILs) + molecular solvents (MSs) (Tariq et al, 2015).…”

“…Tariq et al (2015) selected four binary IL+MS systems composed of a molecular solvent (2-amino-ethanol (2AE) or 3-amino-1-propanol (3AP)) and an IL (from the 1-alkyl- 3-methylimidazolium family ([C n mim] + ) using dicyanamide ([DCA]) or bistriflimide ([Ntf 2 ]) as the anion). All the components forming the four binary systems are completely miscible in the entire composition range and show crossover temperatures where the IL and MS viscosity values are identical (Figure 2).…”

“…The red circles denote for each system the isotherm closest to the viscosity crossover temperature. (Reprinted from Tariq et al, 2015 with permission from Royal Society of Chemistry).…”

Ionic Liquids and Water: Hydrophobicity vs. Hydrophilicity

“…For smaller alcohol alkyl chains, there is a tendency for self-clustering, with percolation of the simulation box by these aggregates with their accommodation throughout the IL due to the influence of the OH groups, an effect that is lost in longer alcohols [ 30 ]. Introducing atoms with lone pairs of electrons capable of accepting a proton and establishing a hydrogen bond with amino-based alcohols adds further possible combinations in which interaction is possible with the IL [ 31 ]. As for ethers, it is one of the few systems with ILs that exhibits phase diagrams characterized by the existence of a lower critical solution temperature—a phenomenon that is related to the breaking-up of the hydrogen-bonded network that can be formed between the functionalized cation of the ionic liquid and the oxygen atom of the ether molecule [ 32 ].…”

Sodium-ion electrolytes based on ionic liquids: a role of cation-anion hydrogen bonding

“…Room-temperature ionic liquids (RTILs) are a large and versatile class of compounds, formally salts, consisting of organic cation and either organic or inorganic anion [1][2][3][4][5][6][7][8][9][10][11][12]. Unlike inorganic salts, RTILs melt at temperatures below 373 K, thanks to their asymmetric shapes and competing coordination sites.…”