Ionic Liquid-Based Microemulsions Research Articles

Ionic Liquid-Based Microemulsions: Efficient Nanoreactors for Synthesis of Core–Shell Nanoparticles under Ambient Conditions

Ionic Liquid-Based Microemulsions: Efficient Nanoreactors for Synthesis of Core–Shell Nanoparticles under Ambient Conditions

Thermodynamically stable ionic liquid microemulsions pioneer pathways for topical delivery and peptide application

Copper peptides (GHK-Cu) are a powerful hair growth promoter with minimal side effects when compared with minoxidil and finasteride; however, challenges in delivering GHK-Cu topically limits their non-invasive applications. Using theoretical calculations and pseudo-ternary phase diagrams, we designed and constructed a thermodynamically stable ionic liquid (IL)-based microemulsion (IL-M), which integrates the high drug solubility of ILs and high skin permeability of microemulsions, thus improving the local delivery of copper peptides by approximately three-fold while retaining their biological function. Experiments in mice validated the effectiveness of our proposed IL-M system. Furthermore, the exact effects of the IL-M system on the expression of growth factors, such as vascular endothelial growth factor, were revealed, and it was found that microemulsion increased the activation of the Wnt/β-catenin signaling pathway, which includes factors involved in hair growth regulation. Overall, the safe and non-invasive IL microemulsion system developed in this study has great potential for the clinical treatment of hair loss.

Efficient extraction of rhenium through demulsification of imidazolium ionic liquid-based microemulsions from aqueous solution

Rhenium has important applications in metallurgy, military, aviation, chemical, and petrochemical industries and related fields. Because the average concentration of rhenium in the Earth’s crust is just one part per billion (ppb), it is necessary to research the separation and extraction of rhenium from its associated minerals or related solutions. In this study, rhenium extraction through demulsification of an alkyl imidazolium ionic liquid-based microemulsion was explored. Alkyl chain length, components of microemulsion, temperature, acid concentration, and competitive ions affecting rhenium extraction were thoroughly considered. The components of the microemulsion had a significant effect on the extraction process. Extraction efficiency improved with the increase in the alkyl chain length, but it decreased with the rising concentration of nitric acid. The concentration of alkyl imidazole cations in the continuous phase had obvious effects on extraction efficiency. Thermodynamic studies showed the process was endothermic and spontaneous. The extraction mechanisms were an anion exchange and electrostatic attraction between the two N atoms of the imidazole ring and water (H2O) or perthenate (ReO4−) forming the complex ([Omim]ReO4)•(HReO4). Thus, the extraction efficiency of the microemulsion system was about 1.6 times greater than that of the performance of ionic liquids alone. A microemulsion system can be damaged by a strong electrostatic repulsion and steric hindrance effect between the adjacent imidazole rings on the interface of the microemulsion droplet after rhenium extraction. The extraction system is a potential application for the selective separation and extraction of rhenium from simulated radionuclide liquid waste through adjustments to the acidity concentration. Findings of this study provide some basic data regarding the technology for separating and extracting rhenium in future.

Electropolymerization of EDOT in an anionic surfactant-stabilized hydrophobic ionic liquid-based microemulsion.

Here, an anionic surfactant [AOT]- (bis-(2-ethylhexyl) sulfosuccinate)-stabilized H2O/[Omim][PF6] (1-octyl-3-methylimidazolium hexafluorophosphate) microemulsion has been tested for the first time as a medium for the electropolymerization of 3,4-ethylenedioxythiophene (EDOT). To formulate AOT-stabilized [Omim][PF6]-based microemulsions of different water contents, the phase triangle was determined at 35 °C. Measurements of the conductivities of the microemulsions, their solubilization capacities toward EDOT and their catalytic effects on EDOT electrooxidation show that the present [AOT]--stabilized ionic liquid microemulsion is a good medium for EDOT electropolymerization. Studies on the process of the electropolymerization of EDOT in this [Omim][PF6]-based microemulsion indicate that the water content (i.e., microstructure) of the microemulsion medium is an important factor affecting the onset potential and the deposition rate of the PEDOT. The morphology and the doping level of the as-prepared PEDOT are also found to be correlated with the water content of the ionic liquid microemulsion. The microemulsion with higher water content results in a PEDOT with better electroactivity and higher doping levels. FTIR spectra and XPS analysis show that the PEDOT electrosynthesized in the microemulsion is co-doped by both [AOT]- and [PF6]-. Compared with the neat [Omim][PF6], the use of the ionic liquid microemulsions can reduce not only the consumption of the expensive ionic liquid, but also the onset potential for the electrooxidation of EDOT. Moreover, by tuning the water content of the medium, the electropolymerization of PEDOT and its electrochemical properties could be regulated accordingly. Under the identical deposited charge, the PEDOT originated from the high water content microemulsion (50% H2O μE) has a higher specific capacitance (124 F g-1) than that from neat [Omim][PF6] (117 F g-1). It follows that the present ionic liquid microemulsion is a good medium for EDOT electropolymerization. The present study opens up a new route for the green and low-cost electrochemical preparation of high-performance PEDOT.

Ti3C2-MXene composite films functionalized with polypyrrole and ionic liquid-based microemulsion particles for supercapacitor applications

Stemming from its unique structure and properties, Ti3C2-MXenes have stood out from the crowd of electrode materials due to effectively ameliorating imperfections of common ones for excellent energy storage. However, a major stumbling block in the further development of MXene-based supercapacitors is the inherent low capacities caused by severe restacking of nanosheets. Herein, we develop a simple, effective and innovative strategy, namely, introducing both polymerized polypyrrole (PPy) particles and ionic liquid (ILs)-based microemulsion particles as “dual spacers”, to fabricate functionalized Ti3C2-MXene composite films for high-performance and wide-temperature application in supercapacitors. The PPy particles acting as one “spacer” circumvent restacking issues of MXene nanosheets, while contribute to desirable capacitance of the hybrid material. ILs-based microemulsions spontaneously adsorbing onto PPy-Ti3C2Tx nanosheets are conceived to be one more liquid “spacer” for fast ion diffusion kinetics and absent electrolyte imbibition steps, which is rarely reported in previous research for MXene-based electrode materials. These features endow the composite films with excellent specific capacitance, rate capability and cycling stability between 4 °C and 50 °C. At room temperature, the symmetric supercapacitor device based on the composite films delivers a maximum gravimetric energy density of 31.2 Wh kg−1 (at 1030.4 W kg−1) and reserves 91% of the initial specific capacitance with a coulombic efficiency of 91% after 2000 cycles. All these impressive results substantiate that the composite films prepared by ingenious structure design showcase huge potentials in advanced MXene-based supercapacitors using various ionic liquid electrolytes.

Ex vivo evaluation of celecoxib release from ionic liquid-based microemulsions and microemulgels for topical applications

The aim of this study was to introduce new ionic liquid (IL)-based microemulsions and microemulgels as topical delivery systems for celecoxib. Ex-vivo diffusion of celecoxib loaded in IL-based microemulsions and microemulgels through the rat skin by using Franz diffusion cell was investigated and compared with traditional microemulsions. The investigated systems composed of the same nonionic surfactant/co-surfactant of tween-80/transcutol®P, and different oil phases of [BMIM][PF6], [OMIM][PF6] and isopropyl myristate, for construction of ILs/W and O/W microemulsions. The particle size of the ILs/W and O/W microemulsion systems was determined by DLS method. The ex-vivo release results of ILs/W and O/W formulations, at similar conditions, showed that the celecoxib permeability of the ILs/W formulations is more than that of the O/W formulation, either as microemulsion or as microemulgel. As an interesting result, the celecoxib release percent and release rate from the ILs/W systems was more and faster than the O/W system. The kinetic mechanism for ILs/W systems had followed from first-order model and for O/W systems followed Higuchi zero-order model.

Recent progress in ionic liquids-based microemulsions

Ionic liquid-based microemulsions have the advantages of both ionic liquids and microemulsions, such as broad thermal stability ranges, strong solubilities, tunable structures, and physico-chemical properties. With unique structural features, ionic liquids can replace any components of traditional microemulsions, and thus find extensive application in the fields of material synthesis, biocatalysis, and drug solubilization and delivery. This paper systematically reviews the component replacement with ionic liquids, introduces the progress in the ionic liquids-based microemulsions in terms of structure, property and application, and discusses the developing trend and major challenges.

One-step fabrication of photoluminescent SiC quantum dots through a radiation technique

The fabrication of PL SiC-QDs by using ionic liquid-based microemulsions combined with electron beam radiation.

Comparison of O/W and IL/W Microemulsion Systems as Potential Carriers of Sparingly Soluble Celecoxib Drug

Active pharmaceutical ingredients with poor solubility in water and some organic solvents are a challenge in the pharmaceutical industry. To overcome this limitation, microemulsion systems are a choice to increase the solubility of a sparingly soluble active ingredient. The purpose of this study is to introduce and compare two types of oil-in-water (O/W) and ionic liquid-in-water (IL/W) microemulsions, which were formulated to increase the solubility of celecoxib as an active pharmaceutical ingredient. The proposed formulations are composed of the same nonionic surfactant/co-surfactant of Tween-80/transcutol®P, and different oil phases of isopropyl myristate, [BMIM][PF6] and [OMIM][PF6]. The pseudo-ternary phase diagrams for the microemulsion systems have been determined at a surfactant-to-co-surfactant mass ratio of 3:1 and 298.15 K. From the microemulsion region of the phase diagrams, four formulations was selected and their physico-chemical properties as density, viscosity, refractive index, electrical conductivity and surface tension were measured at 298.15 K. The solubilities of celecoxib in all selected formulations were also determined and compared. The results show considerable increases in solubility of the celecoxib in the ionic liquid-based microemulsion systems.

Dissipative Particle Dynamics Simulation of Ionic Liquid-Based Microemulsion: Quantitative Properties and Emulsification Mechanism

To study the quantitative properties and the mechanism of the microemulsification process, dissipative particle dynamics (DPD) simulation was utilized to investigate a system that was composed of g...

Ionic Liquid-Based Microemulsions with Reversible Microstructures Regulated by CO2.

CO2-responsive microemulsions based on ionic liquid 1,1,3,3-tetramethylguanidine-oleic acid (TMG-OA) have been designed to provide an approach for reducing the volatilization of amine in amine-containing microemulsions effectively and exhibit reversible transitions of microstructures. The ionic liquid TMG-OA was prepared by the direct neutralization of oleic acid (HOA) and 1,1,3,3-tetramethylguanidine (TMG, one of volatile and toxic amines). From the investigations of nuclear magnetic resonance hydrogen spectrum, pH, thermogravimetry, and automatic interface tension meter, the excellent properties of switchability, stability, and surface activity of TMG-OA were demonstrated, and then the ionic liquid-based microemulsions with CO2 response were prepared with TMG-OA (surfactant), HOA (oil phase), isopropyl alcohol (IPA, cosurfactant), and water. Interestingly, for microemulsions with a higher IPA content (47.42, 44.48 wt %), sizes of microemulsions are increased upon introducing CO2 and decreased upon addition of N2/65 °C. In addition, for microemulsions with a lower IPA content (26.22 wt %), the new microemulsions with different sizes are regenerated after the phase separation of emulsions generated by introducing CO2, and incomplete recovery of microemulsions can be observed upon addition of N2/65 °C. The reversible microstructures are induced by the swelling behavior and the reduced single phase area, which are caused by the reversible conversion between TMG-OA and HOA components.

Effect of radiation on interfacial properties and phase behavior of ionic liquid-based microemulsions

Recently, controlled synthesis of nanoparticles through the use of microemulsions combined with electron-beam or γ irradiation has garnered interest. However, there are rare research about the effect of these radiations on the interfacial properties and phase behavior of microemulsions. Therefore, in this work, we prepared ionic liquid-based microemulsions (IL-Cn-Ms) combining 3-methylimidazolium hexafluorophosphate having different alkyl chain lengths, TX-100, and deionized water and then irradiated them with a high-energy electron beam. The effects of radiation and alkyl chain length on microemulsion microregions, droplet size, surface tension, and solubilization were investigated in detail. Radiation had a negligible effect on the interfacial properties and phase behavior of the IL-Cn-Ms. Interestingly, the droplet size of IL-Cn-Ms increased with the alkyl chain length of the ionic liquid due to the IL interactions at the IL-Cn-Ms interface. Our work provides a preliminary database and presents new opportunities for the combination of ionic liquid-based microemulsions and radiation technology.

Thermally Stable Ionic Liquid-Based Microemulsions for High-Temperature Stabilization of Lysozyme at Nanointerfaces.

The development of new strategies for thermal stability and storage of enzymes is very important, considering the nonretention of catalytic activity by enzymes under harsh conditions of temperature. Following this, herein, a new approach based on the interfacial adsorption of lysozyme (LYZ) at nanointerfaces of ionic liquid (IL)-based microemulsions, for enhanced thermal stability of LYZ, is reported. Microemulsions (MEs) composed of dialkyl imidazolium-based surface active ILs (SAILs) as surfactants, ILs as the nonpolar phase, and ethylene glycol (EG) as the polar phase, without any cosurfactants, have been prepared and characterized in detail. Various regions corresponding to polar-in-IL, bicontinuous, and IL-in-polar phases have been characterized using conductivity measurements. Dynamic light scattering (DLS) measurements have provided insights into the size distribution of microdroplets, whereas temperature-dependent DLS measurements established the thermal stability of the MEs. Nanointerfaces formed by SAILs with EG in thermally stable reverse MEs act as fluid scaffolds to adsorb and provide thermal stability, up to 120 °C, to LYZ. Thermally treated LYZ upon extraction into a buffer shows enzyme activity owing to negligible change in the active site of LYZ, as marked by retention of microenvironment of Trp residues present in the active site of LYZ. The present work is expected to establish a new platform for the development of novel nanointerfaces utilizing biobased components for other biomedical applications.

Mixing oil and water with ionic liquids: bicontinuous microemulsions under confinement.

We report the structural transition of a phosphonium ionic liquid-based microemulsion from the bulk to nanoconfined between atomically flat micas. Upon the nanoconfinement, we observed a firmly surface-adsorbed ionic liquid film that stabilizes the nanoconfined microemulsion. Further confinement (<11 nm) induces rearrangements in the microemulsion culminating into two well-ordered layers with slow dynamics.

Phase Behavior of the Anionic Surfactant [Bmim][AOT]-Stabilized Hydrophobic Ionic Liquid-Based Microemulsions and the Effect of n-Alcohols

In this work, the fishlike phase diagram of the H2O/[Bmim][AOT]/[Bmim][PF6]/n-alcohol as a function of temperature (T) and the mass fraction of [Bmim][AOT] (with or without n-alcohol) in the total mixture (γ) has been observed for the first time at several mass ratios of [Bmim][PF6] to H2O (α) and with different n-alcohols. The larger area of the three-phase region occurs at α ≤ 0.500, and the resulting fish shapes are similar to each other. For a given α, a temperature scan (from lower to higher) at several γ values reveals that the present system forms an upper phase microemulsion first and then a lower phase microemulsion. The formation of hydrophobic ionic liquid-in-water (HIL/W) microemulsion at low temperature and water-in-hydrophobic ionic liquid (W/HIL) microemulsion at high temperature was confirmed by dynamic light scattering and small-angle X-ray scattering techniques. Here, the phase sequence that occurred during the temperature scan is opposite to that of a classic H2O/NaAOT/oil system. At th...

Switchable oil–water phase separation of ionic liquid-based microemulsions by CO2

Stimuli-responsive ionic liquid microemulsions can be reversibly switched from W/O monophase to oil–water phase separation upon alternate bubbling and removal of CO2.

Ionic Liquid-Based Microemulsions in Catalysis.

The design and properties of surface-active ionic liquids that are able to form stable microemulsions with heptane and water are presented, and their promise as reaction media for thermomorphic palladium-catalyzed cross-coupling reactions is demonstrated.

Extraction of palladium (II) by a silicone ionic liquid-based microemulsion system from chloride medium

The silicone ionic liquid, 1-methyl-3-[tri-(trimethylsiloxy)]silylpropyl-imidazolium chloride ([Si4mim]Cl), was first used for the construction of the W/O microemulsion system and the [Si4mim]Cl/n-heptane/n-hexanol/NaCl microemulsion system was applied for palladium extraction for the first time. The stability of [Si4mim]Cl/n-heptane/n-hexanol/NaCl microemulsion system was characterized by the Turbiscan Lab. For the Pd (II) extraction by the [Si4mim]Cl/n-heptane/n-hexanol/NaCl microemulsion system, primary parameters (namely, the vibration time, the [Si4mim]Cl concentration, the phase ratio and the additives) affecting the palladium extraction was investigated to optimize the process. Under the optimum conditions, the extraction percentage of Pd (II) is up to 98%. Afterwards, the ionic-exchange mechanism of Pd (II) extraction by the [Si4mim]Cl/n-heptane/n-hexanol/NaCl microemulsion system was confirmed by the Job Method and analyzed by FT-IR spectra. The stripping of Pd (II) from the microemulsion phase was also studied using the NaCl solutions, indicating a high stripping efficiency. At last, the selectivity of the [Si4mim]Cl/n-heptane/n-hexanol/NaCl microemulsion system to Pd (II) from other metals (Cu (II), Co (II), Ni (II), Fe (III), Al (III) Zn (II), Ce (III), Li (I), Mg (II) and Sn (IV)) was demonstrated to be quite high. The results of our work indicate that the [Si4mim]Cl/n-heptane/n-hexanol/NaCl microemulsion system is a promising approach for Pd (II) extraction.

Polymerization in ionic liquid-based microemulsions

Recent developments of polymerization in ionic liquid-based microemulsions and its applications are reviewed, along with the perspectives and challenges.

Development of Novel Ionic Liquid-Based Microemulsion Formulation for Dermal Delivery of 5-Fluorouracil

The present study was aimed at synthesizing an imidazole-based ionic liquid 1-butyl-3-methylimidazolium bromide (BMIMBr) and subsequent development of a novel ionic liquid-in-oil (IL/o) microemulsion (ME) system for dermal delivery of a poorly permeating drug 5-fluorouracil (5-FU). A significant enhancement in the solubility of 5-FU was observed in BMIMBr. IL/o MEs of 5-FU were prepared using isopropyl myristate, Tween 80/Span 20, and BMIMBr. Results of ex vivo skin permeation studies through mice skin indicated that the selected IL/o ME exhibited 4-fold enhancement in percent drug permeation as compared to aqueous solution, 2.3-fold as compared to hydrophilic ointment, and 1.6-fold greater permeation than water in oil (w/o) ME. The results of in vivo studies against dimethylbenz(a)anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA)-induced mice skin carcinogenesis demonstrated that the IL/o ME could effectively treat skin cancer in 4weeks. In addition, the side effects such as erythema and irritation associated with the conventional formulations were not observed. Histopathological studies showed that the use of IL/o ME caused no anatomic and pathological changes in the skin structure of mice. These studies suggest that the use of IL-based ME system can efficiently enhance the solubility and permeability of 5-FU and hence its therapeutic efficacy.