Dielectric Insights into the Microcosmic Behavior of Ionic Liquid-Based Self-Assembly—Microemulsions/Micelles

Abstract

Dielectric relaxation spectra of ([Bmim][BF]/TX-100/ p-xylene) microemulsions and ([Bmim][BF]/TX-100) micelles were measured. A specific dielectric relaxation changing with the concentration of ionic liquids (ILs) was observed in the range of 10-10 Hz. When dielectric parameters were combined with the Einstein displacement equation and Bruggeman's effective-medium approximation, the interaction between [Bmim][BF] and p-(1,1,3,3-tetramethylbutyl) phenoxypolyoxyethyleneglycol (TX-100) in microemulsions/micelles was presented: because of the electrostatic interaction and van der Waals force, [Bmim][BF] is bound around the polyethylene oxide (PEO) chains of TX-100, and once the electric field is added, ions of [Bmim][BF] will move along the PEO chain. The dependence of dielectric and phase parameters such as relaxation time, permittivity, and volume fraction on the mass fraction of ILs presents an evidence for our proposals about the transition of both systems with the increase of IL content. In addition, it was confirmed that percolation is a unique phenomenon in microemulsions and the percolation mechanism here belongs to static percolation. The transition process of micelles with the change of IL content is presented from the dielectric view.

Dielectric Depiction of 1-Butyl-3-methylimidazolium Tetrafluoroborate/1-Butyl-3-methylimidazolium 1,4-Bis(2-ethylhexyl) Sulfosuccinate/Benzene Microemulsions: Percolation, Interface Polarization, and Electrical Parameters

“…That is to say, the intermediate state between PIL/O and O/PIL is a bicontinuous structure, where oil pipelines and PIL pipelines simultaneously appear. This situation is not only often seen in traditional microemulsions , but is also same as other dense anhydrous IL microemulsion systems, such as [bmim]­[BF 4 ]/TX-100/cyclohexane, [bmim]­[BF 4 ]/TX-100/ p -xylene, [bmim]­[BF 4 ]/TX-100/triethylamine, [bmim]­[BF 4 ]/TX-100/toluene, and [bmim]­[BF 4 ]/ethanol/toluene . Changing the oil phase and using the SAIL [bmim]­[AOT] as the surfactant did not affect the percolation mechanism; the only two factors that may determine the static percolation of the system are the IL acting as the polar phase and the dense system.…”

“…Dielectric relaxation spectrum (DRS) is one of the effective methods to study the physicochemical properties of IL microemulsions. − At present, this method has been used to study the microemulsion formed by IL replacing only water ,− or only oil. ,− , In view of the distinct advantages that dielectric spectra can be used to judge the microemulsion percolation mechanism by multiple physical quantities simultaneously, in these studies, the percolation mechanisms of IL microemulsions such as H 2 O/TX-100/[bmim][PF 4 ], [bmim][BF 4 ]/TX-100/cyclohexane, ethylene glycol/TX-100/[bmim][PF 6 ], , [bmim][BF 4 ]/TX-100/benzene, [bmim][PF 6 ]/TX-100/toluene, [bmim][BF 4 ]/TX-100/ p -xylene, [bmim][BF 4 ]/TX-100/triethylamine, [bmim][BF 4 ]/TX-100/toluene, and [bmim][BF 4 ]/ethanol/toluene were determined as the static percolation by the theoretical analysis of concentration dependence of dc conductivity ,,− ,− and static dielectric constant, , frequency dependence of permittivity ,− and loss angle. − The multipolarization of IL microemulsions has been studied by DRS: the interfacial polarization is observed, ,,,− which is strong evidence that interfaces exist in such systems; other dielectric relaxation mechanisms are directional movement of the IL anions along the PEO chains of TX-100 , or the result of superimposed dipole rotation polarization of cations on the long axis direction and the polarization of the EO segment in TX-100 . The phase parameters, such as the data of dielectric constant and conductivity for each phase, which are used to describe the difference in dielectric properties between dispers...…”

“…Despite the above report, many physical chemistry properties of microemulsions in which ILs replace both water and surfactants at the same time still need to be studied, such as dividing different subregions as traditional microemulsions, , determining the percolation mechanism, studying the multipolarization mechanism, and quantitatively describing the electrical differences of the dispersed phase and continuous phase. Dielectric relaxation spectrum (DRS) is one of the effective methods to study the physicochemical properties of IL microemulsions. − At present, this method has been used to study the microemulsion formed by IL replacing only water ,− or only oil. ,− , In view of the distinct advantages that dielectric spectra can be used to judge the microemulsion percolation mechanism by multiple physical quantities simultaneously, in these studies, the percolation mechanisms of IL microemulsions such as H 2 O/TX-100/[bmim]­[PF 4 ], [bmim]­[BF 4 ]/TX-100/cyclohexane, ethylene glycol/TX-100/[bmim]­[PF 6 ], , [bmim]­[BF 4 ]/TX-100/benzene, [bmim]­[PF 6 ]/TX-100/toluene, [bmim]­[BF 4 ]/TX-100/ p -xylene, [bmim]­[BF 4 ]/TX-100/triethylamine, [bmim]­[BF 4 ]/TX-100/toluene, and [bmim]­[BF 4 ]/ethanol/toluene were determined as the static percolation by the theoretical analysis of concentration dependence of dc conductivity ,,− ,− and static dielectric constant, , frequency dependence of permittivity ,− and loss angle. − The multipolarization of IL microemulsions has been studied by DRS: the interfacial polarization is observed, ,,,− which is strong evidence that interfaces exist in such systems; other dielectric relaxation mechanisms a...…”

Understanding the Droplet Diffusion in Ionic Liquid Microemulsions

“…The electrical conductivity profile for the series is shown in Figure S1 (Supporting Information) which, like viscosity, shows at the onset of similar bicontinuous to the O/IL transition noticeable changes. The values are comparable to previously reported values, ,, although to notethe electrical conductivity keeps increasing beyond the bicontinuous to O/IL transition; for similar systemsbut at much lower TX-100 mass fraction, conductivity was found to rather decrease, ,, although increases were observedparticularly at significantly high surfactant concentration. ,, …”

“…The values are comparable to previously reported values, 19,20,43 although to note�the electrical conductivity keeps increasing beyond the bicontinuous to O/IL transition; for similar systems�but at much lower TX-100 mass fraction, conductivity was found to rather decrease, 19,20,43 although increases were observed�particularly at significantly high surfactant concentration. 15,16,44 The viscosity variation in IL microemulsions has not been extensively reported in the literature; however, compared to the few studies 16,45,46 that addressed this property, the viscosities for the current systems are quite high. Interestingly, the current systems resemble highly viscous aqueous microemulsions containing polymers (amphiphilic or graft copolymers) at high concentration.…”