Investigating Nanostructuring within Imidazolium Ionic Liquids: A Thermodynamic Study Using Photochromic Molecular Probes

Abstract

Following previous studies involving the thermal relaxation of spirocyclic compounds we extended our studies to investigate the formation of nano-structured domains in ionic liquids (ILs). Two compounds, spiropyran (BSP) and spirooxazine (SO) were added to imidazolium cation based ionic liquids with increasing chain lenghts (C 2 -C 12 ). Increasing side-chain length was found to have only minor effects on the rate of thermal relaxation of BSP and SO. BSP was found to be a suitable probe molecule as linear correlations in parameters were observed for this compound. This is believed to be due to the fact that BSP-IL interactions were based on hydrogen bonding between MC BSP and the cation compared to MC SO The resulting reorganisation of the system produced positive entropies of activation, 13.79 J.K -1 .mol -1 for C 4 mIm to 46.15 J.K -1 .mol -1 for C 12 mIm, following an increase in disorder due to probe dye closure from MC to BSP and migration of dye to regions of preferential solvation. The ability for spirocyclic compounds to form both polar and non-polar isomers resulted in the ability to analyse both solvent regions using a single probe dye. Ground state equilibrium, K e , examined non-polar regions of the IL while equilibrium of activation, K ‡ , examined the polar regions. A linear response to side chain length to equilibrium of activation was believed to be due to the fact that polar regions were possibly expanding due to increasing influence of non-polar side chain interactions upon the over solvent structure. The result of such reordering and dispersion of polar regions reduces solvent-solute interactions which increases rate of MC-BSP relaxation.

Vapor pressures of 1,3-dialkylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids with long alkyl chains

“…Nevertheless, the effect of nanostructuration/segregation of ionic liquids on the static and dynamic properties of these compounds has been established in previous works. 33,34,[36][37][38][39][40][41][42] A critical analysis of the enthalpies of vaporization for the [C N-1 C 1 im][NTf 2 ] ionic liquid series and the dependency of the data with the chain length of the alkyl group of the cation has been recently published. 35 Therefore, and considering the fact that literature data for this new ionic liquids are not available, in this work the discussion will be made focusing on the data obtained based on experimental vapor pressures.…”

“…33,34 Despite the controversy around the so called trend shift on the enthalpies of vaporization, 35 the effect nanostructuration in ionic liquids was already detected in several other properties. 33,34,[36][37][38][39][40][41][42] This work presents vapor pressure data for the 1, )] spectrometer, and the solvent used was DMSO D6. The ionic liquids were found to be >99 wt.% purity.…”

Swelling and shrinking behaviour of photoresponsive phosphonium-based ionogel microstructures

“…26 The reason for this difference in trend is not clear at this point, but it may lie in the way the ions interact with the gel polymer chains, and the impact of these interactions on IL nano-domain structure. 27,28 In [P 6,6,6,14 (Figure 3a). As shown in Figure 4 and Figure S6).…”

Layered Structure of Room‐Temperature Ionic Liquids in Microemulsions by Multinuclear NMR Spectroscopic Studies

“…5 For example, a recent report has shown that surfactant–ionic‐liquid‐based microemulsions can be used to produce polymer nanoparticles, gels, and open‐cell porous materials 8g. In the work presented here, we utilized 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([bmim][BF 4 ], Scheme ) as the polar phase for microemulsions; this system is known to form organized structures in the presence of additives12 Researchers have demonstrated nanosized reverse micelles dispersed with Triton X‐100 (TX‐100) in cyclohexane by using [bmim][BF 4 ] 8a. c–e, k, m, p,q Dynamic light scattering (DLS) confirmed that the RTIL microemulsions contained nanosized structures,8p,q and similar to “classic” water‐in‐oil (w/o) microemulsions, the droplet volume of these nanosystems increase regularly as micelles were progressively swollen with added [bmim][BF 4 ] 8m.…”