Protic Ionic Liquids:  Physicochemical Properties and Behavior as Amphiphile Self-Assembly Solvents

Abstract

The physicochemical properties of 22 protic ionic liquids (PILs) and 6 protic molten salts, and the self-assembly behavior of 3 amphiphiles in the PILs, are reported. Structure-property relationships have been explored for the PILs, including the effect of increasing the substitution of ammonium cations and the presence of methoxy and hydroxyl moieties in the cation. Anion choices included the formate, pivalate, trifluoroacetate, nitrate, and hydrogen sulfate anions. This series of PILs had a diverse range of physicochemical properties, with ionic conductivities up to 51.10 mS/cm, viscosities down to 5.4 mPa.s, surface tensions between 38.3 and 82.1 mN/m, and densities between 0.990 and 1.558 g/cm3. PILs were designed with various levels of solvent cohesiveness, as quantified by the Gordon parameter. Fourteen PILs were found to promote the self-assembly of amphiphiles. High-throughput polarized optical microscopy was used to identify lamellar, hexagonal, and bicontinuous cubic amphiphile self-assembly phases. The presence and extent of amphiphile self-assembly have been discussed in terms of the Gordon parameter.

Transport properties in two pyrrolidinium-based protic ionic liquids as determined by conductivity, viscosity and NMR self-diffusion measurements

“…With respect to the anionic species, a higher basicity, larger size, and more pronounced relative capacity to form hydrogen bonds result in more viscous ILs. Thus, due to the acid/base character of PILs, their viscosity depends significantly on hydrogen bonds [27]. At 298 K, the studied PILs displayed viscosity values of 187.…”

“…ILs have reasonably good ionic conductivities (up to 10 mS cm −1 ) as compared to organic solvents/electrolyte systems [32]. PILs, on the other hand, possess generally higher conductivities than their aprotic counterparts [27]. Table 2. were 4.6 and 4.0 mS cm −1 , respectively, and at 363 K, these values were raised to respectively 31.2 and 36.3 mS cm −1 (Fig.…”

“…Indeed, while the viscosity of water, for instance, is only 0.8903 cP at 298 K, the viscosities of ILs typically range from 30 to 100 cP at room temperature, and can reach values as high as 1000 cP in certain cases [27][28][29]. PILs are very sensitive to nature of substituent [29], for example EAF, DEAF and TEAF have respectively 32 cP, 5.4 cP and 5.8 cP [27]. Moreover, IL viscosities appear to be governed also by van der Waals interactions [30] and cationic size [31].…”

Physicochemical and Acid-base Properties of a Series of 2-Hydroxyethylammonium-based Protic Ionic Liquids

“…[33][34][35][36][37] In order to clarify solvent natures, one must have extensive knowledge of physicochemical and Brønsted and/or Lewis acid-base properties of ionic liquids. Experimental results for the physicochemical properties [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] and solvatochromic parameters [53][54][55] of ionic liquids with the hydroxyl groups have been reported.…”

Structural Effects on the Physico‐Chemical and Catalytic Properties of Acidic Ionic Liquids: An Overview

“…In the last three or four years, PILs containing primary, secondary, and tertiary ammonium cations have been extensively investigated by Drummond et al [17,[60][61][62] . The presence of hydroxy groups on PILs leads to higher surface tensions and consequently higher values of the Gordon parameters (the Gordon parameters are generally regarded as measures of cohesiveness of liquids and indications of the driving forces for self-assembly of amphiphiles).…”