Effects of Water on Solvation Layers of Imidazolium-Type Room Temperature Ionic Liquids on Silica and Mica

Abstract

Effects of the addition of water on solvation layers of imidazolium-type room temperature ionic liquids (RT-ILs) have been studied through force curve measurements of atomic force microscopy (AFM). Two kinds of RT-ILs were employed in this study; one is a hydrophilic RT-IL (1-butyl-3-methylimidazolium tetrafluoroborate, BmimBF4), and the other is a hydrophobic one (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, EmimTFSI). These RT-ILs form solvation layers on hydrophilic solid substances (i.e., silica and mica) in the absence of added water. The addition of water into BmimBF4 resulted in the disruption of the solvation layers and then the formation of an interfacial water phase on silica. In contrast, the formation of the interfacial water phase was not evidenced on mica because of the absence of hydrogen-bonding sites on the mica surface. Interestingly, the addition of water into EmimTFSI induced the formation of the interfacial water phase on the two solid surfaces. In the EmimTFSI system, importantly, significantly greater adhesion forces were observed on silica than on mica. This reflects the different formation mechanisms of the interfacial water phase on the two solid surfaces. We conclude that the hydrogen bonding is a key factor in determining whether water molecules can be adsorbed on the solid surfaces, but it is also necessary to take into account the hydrophilic/hydrophobic nature of the RT-ILs.

Effect of water on the interfacial structures of room‐temperature ionic liquids

“…Multiple repulsive layers were observed in the [EMIM][DCN] solution. This phenomenon is often observed in fluorine‐based RTILs . Figure shows the force curve profile of the [EMIM][DCN] solution.…”

“…The thickness of the repulsive layer closest to the solid surface (the first layer) was approximately 0.73 nm (Figure (1)), almost equal to the size of an [EMIM] cation (ionic radius = 0.32 nm) and a [DCN] anion (ionic radius = 0.33 nm) . This layer was considered cation‐rich because mica exhibited a negative potential . The width of the second repulsive layer was approximately 0.74 nm (Figure (2)).…”

“…12,13 This layer was considered cation-rich because mica exhibited a negative potential. 11 The width of the second repulsive layer was approximately 0.74 nm (Figure 3 (2)). This layer was composed of a mixture of cations and anions.…”

Inorganic/Organic Double-Network Ion Gels with Partially Developed Silica-Particle Network

“…[34][35] In addition, it was reported that water molecules could adsorb on silica surface in an ionic liquid by hydrogen bonding. 36 In the same manner, it was considered that ethanol could adsorb on the surface of silica nanoparticles via hydrogen bonds in an ionic liquid. As the result of ethanol adsorption, the formation of hydrogen bonds between the silica nanoparticles could be inhibited.…”

Effect of Surrounding Atmosphere on Friction Properties of Hydrophobic and Hydrophilic Ionic Liquids

“…In addition, emission of HF gas derived from hydrolysis is a concern [36, [44][45][46]. Deterioration of the friction properties and disappearance of the adsorption layer have been reported in other ionic liquids when mixed with water [47][48][49]. However, both negative and positive effects were observed.…”