Ionic liquids in microemulsions

Design Principles and Applications of Ionic Liquids for Transdermal Drug Delivery

Ionic liquids (ILs) are salts with melting points typically <100 °C, composed of specific anions and cations. Recently, IL application has expanded into material engineering and biomedicine. Due to their unique properties, ILs have garnered significant interest in pharmacological research as solubilizers, transdermal absorption enhancers, antibacterial agents, and stabilizers of insoluble pharmaceutical active ingredients. The improvement of skin permeability by ILs is closely associated with their specific physicochemical characteristics, which are identified by their ionic composition. However, the existing literature on transdermal medication administration is insufficient in terms of a comprehensive knowledge base. This review provides a comprehensive assessment of the design principles involved in IL synthesis. Additionally, it discusses the methods utilized to assess skin permeability and provides a focused outline of IL application in transdermal drug administration.

Formulation of a stable diesel microemulsion using eco-friendly ionic liquids and investigation of particle size and fuel properties as an alternative fuel

Ecofriendly ionic liquids (ILs) were synthesized through amidation of ricinoleic acid, the main fatty acid in castor oil, followed by a quaternization reaction to solubilize ethanol in IL/diesel blends at different ratios. As a result, stable and highly renewable, low viscous microemulsion biofuels with high oxygen content were prepared. The prepared fuel samples combine the advantages of green ionic liquids and microemulsion properties. The chemical structures of ILs were confirmed with the aid of NMR and FTIR spectroscopy. DLS analysis revealed that the ethanol particles ranged in size from 8 to 18.1 nm in all samples. As ILs ratios decrease in microemulsion from 37 to 69%, the ethanol particle sizes increase from 10 to 25%. Ethanol shows good solubilization in diesel and IL-1 is more effective than IL-2 in ethanol solubilization at low percentages of ethanol due to more oxygen atoms besides three hydroxyl groups. The ternary phase diagram indicated that the microemulsion area in the case of using IL-1 is larger than that of IL-2. The fuel properties of the prepared microemulsions are nearly close to those of neat diesel and fall within the permitted range of ASTM D975. The viscosity and density values at low ratios of ILs are found to be very close to the values of the neat diesel at different temperatures. The prepared samples show a slight decrease in cetane number and heating value compared to diesel. However, they have improved flash points, cloud points, sulfur content, and acid value. The particle sizes were checked every week and the prepared samples showed high stability with the aid of the synthesized ILs. Moreover, the prepared microemulsions stayed in a transparent appearance for more than a year and no phase separation was observed.

Polymerized and Colloidal Ionic Liquids─Syntheses and Applications

The breadth and importance of polymerized ionic liquids (PILs) are steadily expanding, and this review updates advances and trends in syntheses, properties, and applications over the past five to six years. We begin with an historical overview of the genesis and growth of the PIL field as a subset of materials science. The genesis of ionic liquids (ILs) over nano to meso length-scales exhibiting 0D, 1D, 2D, and 3D topologies defines colloidal ionic liquids, CILs, which compose a subclass of PILs and provide a synthetic bridge between IL monomers (ILMs) and micro to macro-scale PIL materials. The second focus of this review addresses design and syntheses of ILMs and their polymerization reactions to yield PILs and PIL-based materials. A burgeoning diversity of ILMs reflects increasing use of nonimidazolium nuclei and an expanding use of step-growth chemistries in synthesizing PIL materials. Radical chain polymerization remains a primary method of making PILs and reflects an increasing use of controlled polymerization methods. Step-growth chemistries used in creating some CILs utilize extensive cross-linking. This cross-linking is enabled by incorporating reactive functionalities in CILs and PILs, and some of these CILs and PILs may be viewed as exotic cross-linking agents. The third part of this update focuses upon some advances in key properties, including molecular weight, thermal properties, rheology, ion transport, self-healing, and stimuli-responsiveness. Glass transitions, critical solution temperatures, and liquidity are key thermal properties that tie to PIL rheology and viscoelasticity. These properties in turn modulate mechanical properties and ion transport, which are foundational in increasing applications of PILs. Cross-linking in gelation and ionogels and reversible step-growth chemistries are essential for self-healing PILs. Stimuli-responsiveness distinguishes PILs from many other classes of polymers, and it emphasizes the importance of segmentally controlling and tuning solvation in CILs and PILs. The fourth part of this review addresses development of applications, and the diverse scope of such applications supports the increasing importance of PILs in materials science. Adhesion applications are supported by ionogel properties, especially cross-linking and solvation tunable interactions with adjacent phases. Antimicrobial and antifouling applications are consequences of the cationic nature of PILs. Similarly, emulsion and dispersion applications rely on tunable solvation of functional groups and on how such groups interact with continuous phases and substrates. Catalysis is another significant application, and this is an historical tie between ILs and PILs. This component also provides a connection to diverse and porous carbon phases templated by PILs that are catalysts or serve as supports for catalysts. Devices, including sensors and actuators, also rely on solvation tuning and stimuli-responsiveness that include photo and electrochemical stimuli. We conclude our view of applications with 3D printing. The largest components of these applications are energy related and include developments for supercapacitors, batteries, fuel cells, and solar cells. We conclude with our vision of how PIL development will evolve over the next decade.

Energy Applications of Ionic Liquids: Recent Developments and Future Prospects

Ionic liquids (ILs) consisting entirely of ions exhibit many fascinating and tunable properties, making them promising functional materials for a large number of energy-related applications. For example, ILs have been employed as electrolytes for electrochemical energy storage and conversion, as heat transfer fluids and phase-change materials for thermal energy transfer and storage, as solvents and/or catalysts for CO2 capture, CO2 conversion, biomass treatment and biofuel extraction, and as high-energy propellants for aerospace applications. This paper provides an extensive overview on the various energy applications of ILs and offers some thinking and viewpoints on the current challenges and emerging opportunities in each area. The basic fundamentals (structures and properties) of ILs are first introduced. Then, motivations and successful applications of ILs in the energy field are concisely outlined. Later, a detailed review of recent representative works in each area is provided. For each application, the role of ILs and their associated benefits are elaborated. Research trends and insights into the selection of ILs to achieve improved performance are analyzed as well. Challenges and future opportunities are pointed out before the paper is concluded.

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.

Phase studies of ethyl ammonium nitrate (EAN)/sugar surfactant microemulsions: effect of chain length of alkanes and length of the hydrophobic chain of the non-ionic surfactant

Microemulsions were formulated with the ionic liquid ethylammonium nitrate (EAN) used instead of water as the polar phase, hydrocarbon solvents (n-alkanes) and sugar-based non-ionic surfactants, and their phase behaviour and microstructure were investigated. The sugar-based non-ionic surfactants used are non-toxic, biodegradable and environmentally friendly. Due to these properties, their use in microemulsion systems is a clear alternative to the conventionally used non-ionic surfactants from the class of alkyl polyoxyethylene ethers (C i E j ). The influence of n-alkanes with different chain lengths and of sugar-based nonionic surfactants with hydrophobic chains of different lengths on the microemulsion system was also investigated. The results obtained for the microemulsions with EAN described here are similar to those obtained for microemulsion systems formulated with water as the polar solvent. Liquid crystalline (LC) phases were observed in microemulsion systems with sugar-based nonionic surfactants having longer hydrocarbon chains, at lower temperatures and higher surfactant mass fraction.

Using Microemulsions: Formulation Based on Knowledge of Their Mesostructure

Microemulsions, as thermodynamically stable mixtures of oil, water, and surfactant, are known and have been studied for more than 70 years. However, even today there are still quite a number of unclear aspects, and more recent research work has modified and extended our picture. This review gives a short overview of how the understanding of microemulsions has developed, the current view on their properties and structural features, and in particular, how they are related to applications. We also discuss more recent developments regarding nonclassical microemulsions such as surfactant-free (ultraflexible) microemulsions or ones containing uncommon solvents or amphiphiles (like antagonistic salts). These new findings challenge to some extent our previous understanding of microemulsions, which therefore has to be extended to look at the different types of microemulsions in a unified way. In particular, the flexibility of the amphiphilic film is the key property to classify different microemulsion types and their properties in this review. Such a classification of microemulsions requires a thorough determination of their structural properties, and therefore, the experimental methods to determine microemulsion structure and dynamics are reviewed briefly, with a particular emphasis on recent developments in the field of direct imaging by means of electron microscopy. Based on this classification of microemulsions, we then discuss their applications, where the application demands have to be met by the properties of the microemulsion, which in turn are controlled by the flexibility of their amphiphilic interface. Another frequently important aspect for applications is the control of the rheological properties. Normally, microemulsions are low viscous and therefore enhancing viscosity has to be achieved by either having high concentrations (often not wished for) or additives, which do not significantly interfere with the microemulsion. Accordingly, this review gives a comprehensive account of the properties of microemulsions, including most recent developments and bringing them together from a united viewpoint, with an emphasis on how this affects the way of formulating microemulsions for a given application with desired properties.

Biocompatible Solvents and Ionic Liquid-Based Surfactants as Sustainable Components to Formulate Environmentally Friendly Organized Systems

In this review, we deal with the formation and application of biocompatible water-in-oil microemulsions commonly known as reverse micelles (RMs). These RMs are extremely important to facilitate the dissolution of hydrophilic and hydrophobic compounds for biocompatibility in applications in drug delivery, food science, and nanomedicine. The combination of two wisely chosen types of compounds such as biocompatible non-polar solvents and ionic liquids (ILs) with amphiphilic character (surface-active ionic liquids, SAILs) can be used to generate organized systems that perfectly align with the Green Chemistry concepts. Thus, we describe the current state of SAILs (protic and aprotic) to prepare RMs using non-polar but safe solvents such as esters derived from fatty acids, among others. Moreover, the use of the biocompatible solvents as the external phase in RMs and microemulsions/nanoemulsions with the other commonly used biocompatible surfactants is detailed showing the diversity of preparations and important applications. As shown by multiple examples, the properties of the RMs can be modified by changes in the type of surfactant and/or external solvents but a key fact to note is that all these modifications generate novel systems with dissimilar properties. These interesting properties cannot be anticipated or extrapolated, and deep analysis is always required. Finally, the works presented provide valuable information about the use of biocompatible RMs, making them a green and promising alternative toward efficient and sustainable chemistry.

Versatile surface-active ionic liquid: construction of microemulsions and their applications in light harvesting

This article outlines a sustainable method towards the synthesis of advanced materials such as core/shell Quantum Dots (QDs) and their in situ stabilization using microemulsions (MEs). QDs are versatile materials which show unusual optical properties. We have constructed MEs consisting of an Ionic Liquid (IL) based surfactant i.e. choline dioctylsulfosuccinate, [Cho][AOT] as an emulsifier, toluene as a nonpolar phase and water as a polar phase. The system forms a large single-phase region in the phase diagram without any co-surfactant. Spontaneous formation of micelles has been observed and studied through tensiometry and fluorescence and isothermal titration calorimetry (ITC). The exceptional swelling behaviour of the MEs was studied using Dynamic Light Scattering (DLS) and small angle neutron scattering (SANS). In ME droplets, i.e. Reverse Micelles (RMs), we successfully synthesized spherical core/shell QDs (size ∼3 to ∼6 nm) with precise control over the size and morphology. The QDs have been characterized using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Powder X-ray Diffraction (PXRD). QDs stabilized in MEs exhibited excellent optical properties and can be suitably used as light harvesting materials for diverse applications.

Ionic Liquids for Therapeutic and Drug Delivery Applications

BACKGROUND

Ionic liquids (ILs) are ionic compounds with highly tunable and remarkable properties which make them an important candidate in multiple domains such as extraction, synthesis, analytics, catalysis, biotechnology, therapeutics as well as pharmaceutical sciences.

OBJECTIVE

This review systematically highlights the classification, properties and toxicity of ionic liquids. It focuses on exploring the biological activity of ionic liquids, which includes antimicrobial and anticancer property along with an emphasis on the concept of Active Pharmaceutical Ingredient- Ionic Liquids (API-ILs) for explaining the emulsifier and solubility enhancement property of ILs. An elaborative discussion on the application of ILs for the development of oral, transdermal and topical drug delivery systems has also been presented with suitable literature support.

CONCLUSION

Ionic liquids possess exceptional potential in the field of medicine, biology and chemistry.

Ionic liquid-based transdermal delivery of propranolol: a patent evaluation of US2018/0169033A1

Ionic liquids (ILs) are organic salts of asymmetric organic cations and inorganic/organic anions and are considered green alternative to organic solvents. ILs have high thermal stability, low volatility, low toxicity and high biodegradability. ILs are frequently used for enhancing the solubility and stability of active pharmaceutical ingredients. This study describes an invention related to the preparation of amorphous melts of propranolol incorporated into transdermal patches for infantile hemangioma intervention. Reduction in skin irritation and a significant increase in transdermal permeability of propranolol from its amorphous melts was reported. However, toxicity and stability issues of the IL-based active pharmaceutical ingredients and their drug delivery systems are yet to be established from regulatory perspective before exploiting commercial viability of these forms.

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.

Microstructure of ionic liquid (EAN)-rich and oil-rich microemulsions studied by SANS

In a previous study we investigated the phase behavior of microemulsions consisting of the ionic liquid ethylammonium nitrate (EAN), an n-alkane and a nonionic alkyl polyglycolether (CiEj). We found the same general trends as for the aqueous counterparts, i.e. a transition from an oil-in-EAN microemulsion via a bicontinuous microemulsion to an EAN-in-oil microemulsion with increasing temperature. However, unlike what happens in the corresponding aqueous systems, in EAN-in-oil microemulsions only a very small amount of EAN was detected by NMR-measurements. This is why we investigated the phase behavior and microstructure of EAN-rich n-dodecane-in-EAN microemulsions and oil-rich EAN-in-n-octane microemulsions. We found that the ionic liquid emulsification failure boundary has an extraordinarily small slope, which suggests that the amphiphilic film loses its ability to solubilize EAN with an increase in temperature by only a few degrees. The analysis of the small angle neutron scattering (SANS) curves unambiguously shows that this behavior is due to the fact that the EAN molecules form a substructure with a characteristic length scale of Λ ≈ 8 Å inside the EAN-in-oil droplets. In more detail, the analysis of the SANS data with the GIFT method revealed a transition from spherical to cylindrical structures approaching the respective critical endpoint temperatures. By using the respective form factors and combining them with a Gaussian spatial intensity distribution to account for the EAN sub-structure we were able to describe the scattering curves nearly quantitatively.

Surfactant-Free Microemulsions of 1-Butyl-3-methylimidazolium Hexafluorophosphate, Diethylammonium Formate, and Water

Surfactant-free microemulsions (SFMEs) are a unique kind of microemulsion, which form from immiscible fluids (i.e., oil and water phases) in the presence of amphi-solvents rather than traditional surfactants. In comparison with traditional surfactant-based microemulsions (SBMEs), SFMEs have received much less attention, and the current understanding of the unique system is very limited. Herein, we report a SFME consisting of the hydrophobic ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF₆), the protic IL diethylammonium formate (DEAF), and water, in which the bmimPF₆ and DEAF are used as the oil phase and amphi-solvent, respectively. Three kinds of microstructures, namely, water-in-bmimPF₆ (W/IL), bicontinuous (BC), and bmimPF₆-in-water (IL/W), are identified for the SFME, using cyclic voltammetry, cryo-TEM, and DLS techniques. Especially, the volumetric and surface free energy properties of the SFME are investigated by excess molar volume ( V_m^E) and surface tension (γ) measurements, and they are found to be similar to those of SBMEs. Discontinuous changes in V_m^E and γ with the system compositions are observed as the system microstructures change, which can be used to identify the structural transition of SFMEs. We think this study provides a better understanding of SFME features.

Porous Polyelectrolytes: The Interplay of Charge and Pores for New Functionalities

The past decade has witnessed rapid advances in porous polyelectrolytes and there is tremendous interest in their synthesis as well as their applications in environmental, energy, biomedicine, and catalysis technologies. Research on porous polyelectrolytes is motivated by the flexible choice of functional organic groups and processing technologies as well as the synergy of the charge and pores spanning length scales from individual polyelectrolyte backbones to their nano-/micro-superstructures. This Review surveys recent progress in porous polyelectrolytes including membranes, particles, scaffolds, and high surface area powders/resins as well as their derivatives. The focus is the interplay between surface chemistry, Columbic interaction, and pore confinement that defines new chemistry and physics in such materials for applications in energy conversion, molecular separation, water purification, sensing/actuation, catalysis, tissue engineering, and nanomedicine.

Frontiers in poly(ionic liquid)s: syntheses and applications

We review recent works on the synthesis and application of poly(ionic liquid)s (PILs). Novel chemical structures, different synthetic strategies and controllable morphologies are introduced as a supplement to PIL systems already reported. The primary properties determining applications, such as ionic conductivity, aqueous solubility, thermodynamic stability and electrochemical/chemical durability, are discussed. Furthermore, the near-term applications of PILs in multiple fields, such as their use in electrochemical energy materials, stimuli-responsive materials, carbon materials, and antimicrobial materials, in catalysis, in sensors, in absorption and in separation materials, as well as several special-interest applications, are described in detail. We also discuss the limitations of PIL applications, efforts to improve PIL physics, and likely future developments.

Phase behaviors and characterization of magnetic microemulsions containing pentaalkylguanidinium-based magnetic room-temperature ionic liquids (MRTILs)

Strong magnetic susceptibility and low viscosity magnetic microemulsions containing pentaalkylguanidinium-based magnetic room temperature ionic liquids.

Basic ionic liquid as catalyst and surfactant: green synthesis of quinazolinone in aqueous media

Basic imidazolium-based ionic liquids not only possess the extraordinary physicochemical properties of ionic liquids, but also have excellent basicity and surfactivity. 1-Propyl-3-alkylimidazole hydroxide ionic liquids ([PRIm][OH]) were synthesized and their catalytic and surfactant behavior were studied in this work. [PRIm][OH] owned excellent surfactivity, and their alkyl chains and ion pairs benefit hydrophobicity and hydrophilicity respectively. The surfactivity of [PRIm][OH] increased with increasing alkyl chain length. [PRIm][OH] showed better catalytic performance than NaOH in the condensation of 2-aminobenzonitrile with cyclohexanone in aqueous medium, and the catalytic performance was well coincident with their surfactant behavior. [PRIm][OH] could decrease the interfacial tension of solvent effectively and form micelles in water. The formed micelles could solubilise more reactants into water and effectively increase the chance of contact between reactants and catalytic active sites. The catalyst dosage obviously affected catalytic performance. The catalytic system is a promising recyclable system.

[PRIm][OH] showed excellent catalytic properties in synthesis of quinazolinone in aqueous medium, owing to its excellent surfactivity and basicity.

One-step mild biorefinery of functional biomolecules from microalgae extracts

Fractionation of complex matrices such as biomass into diverse functional biomolecules without disrupting the biomolecule functionalities is a real challenge.

Phase Behavior and Solubilization of Microemulsions Containing C16mimBr with Different Oil-Water Ratios

The effects of oil-water ratios (α) on the composition of the balanced interfacial layer and the optimum solubilization of microemulsions C16mimBr/butan-1-ol/oil (octane, decane, dodecane)/5% NaCl solution were investigated. As α increases, the alcohol solubility in water and oil phases (Sa) in the microemulsions also tends to increase. The reason is the relatively high solubility of the alcohol in the oil phase compared to the solubility in water. When α increases, the number of surfactant ( n s s ${\rm{n}}_{\rm{s}}^{\rm{s}}$ ) and co-surfactant ( n a s ${\rm{n}}_{\rm{a}}^{\rm{s}}$ ) molecules required to balance the interface layer and the proportion of alcohol in the interfacial layer (AS) increase but the solubilization capacity (SP*) decreases. When the total mass of water and oil is unchanged, the solubilization capacity of the microemulsion systems is lower the higher the relative content of oil is. The effects of different oils, salinity and temperature on the composition of the balanced interfacial layer and the solubilization of microemulsions were also investigated.

Choline- versus imidazole-based ionic liquids as functional ingredients in topical delivery systems: cytotoxicity, solubility, and skin permeation studies

BACKGROUND

Poor drug solubility represents a problem for the development of topical formulations. Since ionic liquids (ILs) can be placed in either lipophilic or hydrophilic solutions, they may be advantageous vehicles in such delivery systems. Nonetheless, it is vital to determine their usefulness when used at concentrations were cell viability is maintained, which was considered herein.

METHOD

Five different ILs were prepared-three imidazole-based ILs: [C2mim][Br], [C4mim][Br], and [C6mim][Br]; and two choline-based ILs: [Cho][Phe] and [Cho][Glu]. Their cytotoxicity in human keratinocytes (HaCat cells), their influence in drug solubility and in percutaneous permeation, using pig skin membranes, was evaluated.

RESULTS

Caffeine and salicylic acid were used as model actives. Choline-based ILs proved to be more suitable as functional ingredients, since they showed higher impact on drug solubility and a lower cytotoxicity. The major solubility enhancement was observed for caffeine and further solubility studies were carried out with this active in several concentrations of the choline-based ILs (0.1; 0.2; 0.5; 1.0; 3.0 and 5.0%, w/w) at 25 °C and 32 °C. Solubility was greatly influenced by concentrations up to 0.5%. The choline-based ILs showed no significant impact on the skin permeation, for both actives. The size of the imidazole-based ILs alkyl chain enhances the caffeine solubility and permeation, but also the ILs cytotoxicity. Stable O/W emulsions and gels were prepared containing the less toxic choline-based ILs and caffeine.

CONCLUSIONS

Our results indicate that the choline-based ILs were effective functional ingredients, since, when used at nontoxic concentrations, they allowed a higher drug loading, while maintaining the stability of the formulations.

Cholesterol Based Surface Active Ionic Liquid That Can Form Microemulsions and Spontaneous Vesicles

In this article, we have reported the synthesis and physicochemical characterization of a novel l-glycine amino acid derived cholesterol based surface active ionic liquid (SAIL). This SAIL has been explored for the preparation of ionic liquid (IL)-in-oil microemulsions and vesicles. The formation of IL-in-oil microemulsion is characterized by construction of a ternary phase diagram, dynamic light scattering (DLS) measurement, proton nuclear magnetic resonance (¹H NMR) study, fluorescence measurement using coumarin 480 (C-480) as a molecular probe, and also by recording the diffusion behavior of the molecular probe rhodamine 6G (R6G) in microemulsion droplets through the fluorescence correlation spectroscopy (FCS) technique. Similarly, the spontaneous vesicle formation from the SAIL in water has been established using DLS, transmission electron microscopy (TEM), cryogenic-transmission electron microscopy (cryo-TEM), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), FCS, and fluorescence lifetime imaging microscopy (FLIM) measurements. These aggregates may potentially serve as good biomimicking models and possible drug carriers.

Ionic liquid and nanoparticle hybrid systems: Emerging applications

Having novel electronic and optical properties that emanate from their nano-scale dimensions, nanoparticles are central to numerous applications. Ionic liquids can confer to nanoparticle chemical protection and physicochemical property enhancement through intermolecular interactions and can consequently improve the stability and reusability of nanoparticle for various operations. With an aim to combine the novel properties of nanoparticles and ionic liquids, different structures have been generated, based on a balance of several intermolecular interactions. Such ionic liquid and nanoparticle hybrids are showing great potential in diverse applications. In this review, we first introduce various types of ionic liquid and nanoparticle hybrids, including nanoparticle colloidal dispersions in ionic liquids, ionic liquid-grafted nanoparticles, and nanoparticle-stabilized ionic liquid-based emulsions. Such hybrid materials exhibit interesting synergisms. We then highlight representative applications of ionic liquid and nanoparticle hybrids in the catalysis, electrochemistry and separations fields. Such hybrids can attain better stability and higher efficiency under a broad range of conditions. Novel and enhanced performance can be achieved in these applications by combining desired properties of ionic liquids and of nanoparticles within an appropriate hybrid nanostructure.

Surfactant-free microemulsions of 1-butyl-3-methylimidazolium hexafluorophosphate, propylamine nitrate, and water

Generally, surfactants (or amphiphiles) are believed to be necessary components of microemulsions. However, it has been demonstrated that, in the absence of traditional surfactants, microemulsions can also form from a ternary system of two immiscible fluids (i.e., oil and water phases) and an amphi-solvent, but the current understanding of such surfactant-free microemulsions (SFMEs) is very limited. Herein, we report an SFME consisting of the hydrophobic ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF₆), the protic IL propylamine nitrate (PAN), and water, in which bmimPF₆ and PAN are used as the oil phase and the amphi-solvent, respectively. The microstructures and structural transitions of the SFME were investigated using cyclic voltammetry, fluorescence spectroscopy, and ultraviolet-visible spectroscopy. The SFME exhibited water-in-bmimPF₆ (W/IL), bicontinuous (BC), and bmimPF₆-in-water (IL/W) microstructures, depending on the composition of the ternary system, similar to the case of traditional surfactant-based microemulsions (SBMEs). The three kinds of microstructures were confirmed by cryogenic transmission electron microscopy (cryo-TEM) observations. To the best of our knowledge, this is the first report on SFMEs composed of two ILs as components, especially where one is used as the amphi-solvent.