Structural Studies of 1‐Butyl‐3‐methylimidazolium Tetrafluoroborate/TX‐100/ p‐Xylene Ionic Liquid Microemulsions

Abstract

The ionic liquid (IL) 1‐butyl‐3‐methylimidazolium tetrafluoroborate (bmimBF4) forms nonaqueous microemulsions with p‐xylene, with the aid of the nonionic surfactant TX‐100. The phase behavior of the ternary system is investigated, and three microregions of the microemulsions—ionic liquid‐in‐oil (IL/O), bicontinuous, and oil‐in‐ionic liquid (O/IL)—are identified by conductivity measurements, according to percolation theory. On the basis of a phase diagram, a series of IL/O microemulsions are chosen and characterized by dynamic light scattering (DLS). The size of aggregates increases on increasing the amount of added polar component (bmimBF4), which is a similar phenomenon to that observed for typical water‐in‐oil (W/O) microemulsions, suggesting the formation of IL/O microemulsions. The microstructural characteristics of the microemulsions are investigated by FTIR and 1H NMR spectroscopy. The results indicate that the interaction between the electronegative oxygen atoms of the oxyethylene (OE) units in TX‐100 and the electropositive imidazolium ring may be the driving force for the solubilization of bmimBF4 into the core of the TX‐100 aggregates. In addition, the micropolarity of the microemulsions is investigated by using methyl orange (MO) as a UV/Vis spectroscopic probe. A relatively constant polarity of the microemulsion droplets is obtained in the IL microemulsion. Finally, a plausible structure for the IL/O microemulsion is presented.

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

“…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.…”

Various Self-Assembly Behaviors of Amphiphilic Molecules in Ionic Liquids

“…Recently, the formation mechanism of the bmimBF 4 -in-p-xylene reverse IL microemulsion has been also proposed by Zheng's group [35]. The authors discovered that the terminal hydroxyl stretching of Triton X-100 gradually shifts to a high-frequency region of the FTIR spectrum with increasing bmimBF 4 content because the hydrogen bonds between hydroxyl and oxyethylene (OE) units of Triton X-100 were weakened by the formation of electrostatic attraction between the electronegative oxygen atoms of the OE units and the positively charged imidazolium cation of bmimBF 4 .…”

Supramolecular Structures in the Presence of Ionic Liquids

“…First of all, IL based microemulsions, in which ILs replaced water of traditional microemulsions, have been extensively characterized by a number of techniques. Microregion of phase diagram of IL based microemulsions was detected by cyclic voltammetric technique (Gao et al, 2006a), electrical conductivity (Gao et al, 2004;Gao et al, 2006b;Gao et al, 2007b;Gao et al, 2006d;Li et al, 2007b), and direct observation, where the phase boundaries were determined by observing the transition from transparency to turbidity (Cheng et al, 2007a;Cheng et al, 2007b;Cheng et al, 2008;Gao et al, 2005b;. Based on the phase diagram, DLS (Cheng et al, 2007a;Gao et al, 2004;Gao et al, 2006b;Gao et al, 2008b;Gao et al, 2005b;Li et al, 2007b), FFEM (Cheng et al, 2007a;Gao et al, 2004;Gao et al, 2008b), small-angle X-ray scattering (SAXS) and smallangle neutron scattering (SANS) (Eastoe et al, 2005) have been applied to characterize the microemulsions with polar IL cores.…”

“…These techniques proved the swollen of reversed micelle with the addition of IL, which indicated the formation of reversed microemulsion. More detailed information was gained through FTIR (Gao et al, 2006b), 1 H NMR (Gao et al, 2006b;Gao et al, 2008b), UV-vis spectroscopy (Gao et al, 2006b;Gao et al, 2008b;Gao et al, 2005b;Li et al, 2007b) and conductivity measurements (Gao et al, 2006b;Gao et al, 2008b;Li et al, 2005a). Sarkar and his coworkers (Adhikari et al, 2007;Chakrabarty et al, 2005;Seth et al, 2006Seth et al, , 2007aSeth et al, 2007b) initiated the work of applying steady-state and time-resolved fluorescence spectroscopy to investigate IL based microemulsions.…”

“…The results showed the solvation time inside the polar cores of the microemulsions was retarded compared to that in neat IL because of restrictions in the ionic motions imposed by the microemulsions. Li et al studied the reversed microemulsion of TX-100 in toluene with [C 4 4 ]/TX-100/p-xylene reversed microemulsion was investigated and a plausible structure with "IL pool" was presented (Gao et al, 2006b). It was proposed that the electropositive imidazolium ring of IL destroyed the hydrogen-bonding between TX-100 molecules.…”