Influence of Temperature and Molecular Structure on Ionic Liquid Solvation Layers

Abstract

Atomic force microscopy (AFM) force profiling is used to investigate the structure of adsorbed and solvation layers formed on a mica surface by various room temperature ionic liquids (ILs) ethylammonium nitrate (EAN), ethanolammonium nitrate (EtAN), ethylammonium formate (EAF), propylammonium formate (PAF), ethylmethylammonium formate (EMAF), and dimethylethylammonium formate (DMEAF). At least seven layers are observed for EAN at 14 degrees C (melting point 13 degrees C), decreasing as the temperature is increased to 30 degrees C due to thermal energy disrupting solvophobic forces that lead to segregation of cation alkyl tails from the charged ammonium and nitrate moieties. The number and properties of the solvation layers can also be controlled by introducing an alcohol moiety to the cation's alkyl tail (EtAN), or by replacing the nitrate anion with formate (EAF and PAF), even leading to the detection of distinct cation and anion sublayers. Substitution of primary by secondary or tertiary ammonium cations reduces the number of solvation layers formed, and also weakens the cation layer adsorbed onto mica. The observed solvation and adsorbed layer structures are discussed in terms of the intermolecular cohesive forces within the ILs.

Study of a shear thickening fluid: the dispersions of silica nanoparticles in 1-butyl-3-methylimidazolium tetrafluoroborate

“…In addition, the thermal motion of nanoparticles hinders the aggregation in dispersions, and therefore, the s c increases while the temperature changes from low (30°C) to high (50°C). However, the solvation force of silica nanoparticles will decrease at higher temperatures (Wakeham et al 2009). So that the s c increases slightly at higher temperatures (70 and 100°C).…”

Protic Ionic Liquids: Evolving Structure–Property Relationships and Expanding Applications

“…The layers at the surface have been attributed as being governed by bulk structure, which is orientated by the surface, and not due to surface-induced layering. 198 Atomic force microscopy (AFM) has been extensively used to obtain information about the structure of various PILs at interfaces through characterizing their solvation layers. An analogous method with the surface force apparatus was first used for PILs in 1988, using EAN and its mixtures with water on molecularly smooth mica surfaces.…”

The Electrode/Ionic Liquid Interface: Electric Double Layer and Metal Electrodeposition

“…Stimulated by the interest in the important double-layer structure of complex electrode/ionic liquid interfaces, AFM [70][71][72][73] has also been applied in recent years. Benefiting from the long-range tip-sample interactions, AFM investigations of the diffuse layer of the electric double layer in ionic liquids have been carried out in recent years by Atkin et al [70,71] The number of AFM studies in ionic liquids is, however, rather limited at present.…”

“…Benefiting from the long-range tip-sample interactions, AFM investigations of the diffuse layer of the electric double layer in ionic liquids have been carried out in recent years by Atkin et al [70,71] The number of AFM studies in ionic liquids is, however, rather limited at present.…”