Comparing the structure of different ionic liquid series: Bistriflamide v. hexafluorophosphate; pure v. equimolar mixtures

Emerging Evidences of Mesoscopic-Scale Complexity in Neat Ionic Liquids and Their Mixtures

“…Among them, we would like to mention the class of DSILs composed by mixing [C n mim]­[Tf 2 N] and [C p mim]­[Tf 2 N], with n ≠ p ; they share the anion but are characterized by cations with potentially very different chain lengths. A similar kind of DSILs has been explored in the past (e.g., see refs , , and ), showing that this class of homogeneous mixtures is characterized by quasi-ideal behavior (with larger and larger deviations from this trend when increasing the difference between n and p ) due to the lack of large cross-interactions between the mixed components (as both polar and apolar interactions remain appreciably similar upon mixing). Moreover, an intermixing of the chains with different length building up apolar domains has been observed both experimentally and by simulations .…”

Dynamic-Mechanical and Dielectric Evidence of Long-Lived Mesoscale Organization in Ionic Liquids

“…The molecular structures of the constituent ions and, consequently, the resultant intermolecular interactions, are central to tuning their physicochemical properties such as viscosity, ionic conductivity, density, thermal and electrochemical stability, and polarity. There has been a concerted effort to understand the impact of molecular organization on physicochemical properties of ILs during the past 2 decades. , A recent advance in this respect is the observation of mesoscale organization in bulk ILs arising from the hydrophobic aggregation of extended alkyl tails located on the ionic head groups of a variety of imidazolium, pyridinium, pyrrolidinium, phosphonium, and ammonium cations. − Due to their ability to solvate both polar and nonpolar molecules, the formation of such nanoscale aggregates could provide ILs with possible advantages for a variety of solvent applications such as polymerization, organic synthesis and catalysis, as well as nanoparticle growth. ,,− Until now, experimental evidence of mesoscale organization has been mainly provided by observation of structural features from low-momentum transfer ( q ) peaks in X-ray and neutron scattering functions. Coupled with molecular dynamics simulations, the structure functions reveal the existence of complex architectures ranging from micellar-like spherical aggregates to extended bicontinuous structures as a function of the alkyl chain length. − The influence of these structures on the physicochemical properties of ILs depends strongly on the lifetimes of the nanoscale aggregates. − However, neutron spin echo (NSE) spectroscopy is one of the few techniques currently known to be capable of probing such dynamics, albeit at rather short time scales. ,, These measurements are tedious to carry out as they require deuterated IL samples and access to suitable neutron facilities.…”

“…There has been a concerted effort to understand the impact of molecular organization on physicochemical properties of ILs during the past 2 decades. , A recent advance in this respect is the observation of mesoscale organization in bulk ILs arising from the hydrophobic aggregation of extended alkyl tails located on the ionic head groups of a variety of imidazolium, pyridinium, pyrrolidinium, phosphonium, and ammonium cations. − Due to their ability to solvate both polar and nonpolar molecules, the formation of such nanoscale aggregates could provide ILs with possible advantages for a variety of solvent applications such as polymerization, organic synthesis and catalysis, as well as nanoparticle growth. ,,− Until now, experimental evidence of mesoscale organization has been mainly provided by observation of structural features from low-momentum transfer ( q ) peaks in X-ray and neutron scattering functions. Coupled with molecular dynamics simulations, the structure functions reveal the existence of complex architectures ranging from micellar-like spherical aggregates to extended bicontinuous structures as a function of the alkyl chain length. − The influence of these structures on the physicochemical properties of ILs depends strongly on the lifetimes of the nanoscale aggregates. − However, neutron spin echo (NSE) spectroscopy is one of the few techniques currently known to be capable of probing such dynamics, albeit at rather short time scales. ,, These measurements are tedious to carry out as they require deuterated IL samples and access to suitable neutron facilities. To date, NSE data for only two ILs, namely, 1-octyl-3-methylimidazolium and 1-hexyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide, have been reported in the literature. ,, Other studies involving optical Kerr effect and dielectric spectroscopy at time scales faster than nanoseconds have reported slow, sub-α relaxation modes, attributed to the existence of mesoscale aggregation, in the recent past. , The question regarding whether the nanostructures observed in imidazolium-based ILs have lifetimes beyond a few nanoseconds has remained unanswered.…”

Exploring the Use of Ionic Liquid Mixtures to Enhance the Performance of Dicationic Ionic Liquids

“…Such techniques have been applied to mixtures of ILs with molecular solvents, neutral solutes and inorganic salts 49 as well as mixtures of ILs 50 with different cation chain lengths 51 and anions, 52,53 however we are not aware of any similar studies on IL mixtures of the complexity of those studied here.…”