Shifts in the temperature of maximum density (TMD) of ionic liquid aqueous solutions

Abstract

This work investigates for the first time shifts in the temperature of maximum density (TMD) of water caused by ionic liquid solutes. A vast amount of high-precision volumetric data--more than 6000 equilibrated (static) high-precision density determination corresponding to ∼90 distinct ionic liquid aqueous solutions of 28 different types of ionic liquid--allowed us to analyze the TMD shifts for different homologous series or similar sets of ionic solutes and explain the overall effects in terms of hydrophobic, electrostatic and hydrogen-bonding contributions. The differences between the observed TMD shifts in the -2 < t/°C < 4 range and salting-in or salting-out effects produced by the same type of ions in aqueous solutions at higher temperatures are discussed taking into account the different types of possible solute-water interactions that can modify the structure of the aqueous phase. The results also reveal different insights concerning the nature of the ions that constitute typical ionic liquids and are consistent with previous results that established hydrophobic and hydrophilic scales for ionic liquid ions based on their specific interactions with water and other probe molecules.

Ionic liquids and deep eutectic solvents for lignocellulosic biomass fractionation

“…83,84,85,86 Literature reviews of thermophysical properties were published, describing the main aspects of the effect of the cation or anion, impurities and methodologies. 87,40,84,88,85,86,89,90,91 DESs present densities within the same range of the ILs, being higher than water. Recently, hydrophobic DESs consisting of decanoic acid and quaternary ammonium salts have been reported in the literature, with densities within the range of 889 to 942 kg·m −3 .…”

Temperature of maximum density and excess properties of short-chain alcohol aqueous solutions: A simplified model simulation study

“…In this respect, concerning the density anomaly, solutes can be classified into two groups, namely "structure-makers" (as they increase the TMD when added to water) or "structure-breakers" (decrease the TMD) [8,9]. It has been found that solutes whose molecules do not join the hydrogen bond network, such as electrolytes [10], room temperature ionic liquids [11], or polar substances without H-bond active groups [12] (e.g. acetone, acetonytrile, tetrahydrofurane, among others) induce a decrease of the TMD.…”

Temperature-dependent optoacoustic response and transient through zero Grüneisen parameter in optically contrasted media

“…On the other hand, Despretz constants for the sulfate salts are about 170 times smaller than the Despretz constant of hemoglobin evaluated from the T 0 of whole blood. The interpretation of the Despretz constant is not straightforward and known to be dependent on charge, size and shape of ions [58], [59]. At low concentrations (0–0.3 mol/kg) of ions, the Despretz constant can be rationalized through the linear dependence of K DM on the ionic radii.…”

“…However, the relationship between K DM and ionic radii cannot be extrapolated to multi-domain protein molecules of hemoglobin, which are packed inside erythrocytes at extreme concentrations. The hemoglobin molecule has a complex distribution of surface electrical charge and thermodynamic macro effects contributing to the Despretz constant should be considered through the entire prism of hydrophobic, electrostatic and hydrogen-bond interactions [59].…”