Role of Solubilized Water in the Reverse Ionic Liquid Microemulsion of 1-Butyl-3-methylimidazolium Tetrafluoroborate/TX-100/Benzene

Abstract

The ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) can form nonaqueous microemulsions with benzene by the aid of nonionic surfactant TX-100. The effect of water on ionic liquid-in-oil (IL/O) microemulsions was studied, and it was shown that the addition of small amount of water to the IL microemulsion contributed to the stability of microemulsion and thus increased the amount of solubilized bmimBF4 in the microemulsion. The conductivity measurements also showed that the attractive interactions between IL microdroplets were weakened, that is, the IL/O microemulsion becomes more stable in the present of some water. Fourier transform IR was carried out to analyze the states of the added water, and the result showed that these water molecules mainly behaved as bound water and trapped water, indicating that the water molecules are located in the palisade layers of the IL/O microemulsion. Furthermore, 1H NMR and 19F NMR spectra suggested that the added water molecules built the hydrogen binding network of imidazolium cations and H2O, BF4- anion and H2O, and at the same time the electronegative oxygen atoms of the oxyethylene units of TX-100 and water in the palisade layers, which made the palisade layers more firm and thus increased the stability of the microemulsion. The study can help in further understanding the formation mechanism of microemulsions. In addition, the characteristic solubilization behavior of the added water can provide an aqueous interface film for hydrolysis reactions and therefore may be used as an ideal medium to prepare porous or hollow nanomaterials.

The effect of water on the microstructure and properties of benzene/[bmim][AOT]/[bmim][BF4] microemulsions

“…This is opposite to the result of the Triton X-100 based system, indicating that the driving force for the formation of microemulsion may be different. 15 In the currently studied microemulsions, both the headgroups of …”

“…3 These properties have also led to intense interest in these materials as novel solvents in a range of electrochemical applications. 4 Particular interest has been shown in the self-aggregation of amphiphilic molecules in the ILs, such as micelles, [5][6][7][8][9] microemulsions, [10][11][12][13][14][15] liquid crystals, 16 ion gels, 17 and vesicles. 18 The microstructure and unique properties of these aggregates have been significantly investigated.…”

“…19 Recent work has been concerned with the formation mechanism of the surfactant aggregations and more attention is especially paid to the IL-containing microemulsions stabilized by nonionic surfactants. 15,[20][21][22] Several reviews on the actual state of the art of ILs and microemulsions have also been published. [23][24][25][26] Gao et al were the first to discover that [bmim] [BF 4 ] assembles in polar nanosized droplets when dispersed in cyclohexane as solvent.…”

“…Water has been demonstrated to have a significant effect on the microstructure of [bmim] [BF 4 ]-in-benzene microemulsions. 15 A hydrogen binding network within the palisade layer of nonionic Triton X-100 was formed when small amounts of water were added to the [bmim] [BF 4 ]-in-benzene reverse microemulsion, which made the microemulsion system more stable, and therefore adding water unexpectedly increases the amount of solubilized [bmim] [BF 4 ] in the microemulsions. 15 To date, almost all research on the self-assembly of surfactants in ILs has exclusively focused on using nonionic surfactants, like Triton X-100, Tween 20 and Brij 30.…”

“…15 A hydrogen binding network within the palisade layer of nonionic Triton X-100 was formed when small amounts of water were added to the [bmim] [BF 4 ]-in-benzene reverse microemulsion, which made the microemulsion system more stable, and therefore adding water unexpectedly increases the amount of solubilized [bmim] [BF 4 ] in the microemulsions. 15 To date, almost all research on the self-assembly of surfactants in ILs has exclusively focused on using nonionic surfactants, like Triton X-100, Tween 20 and Brij 30. 26 44,45 We noted that the phase behavior of both microemulsions has many features in common with the corresponding aqueous systems.…”