Self-assembly Of Ionic Liquid Research Articles

Effect of different counterions on the self-assembly structures and properties of imidazole based ionic liquids surfactant: A molecular dynamics study

Self-assembly of ionic liquids (ILs) in solution has attracted wide attention due to their potential applications in various fields. The nature of counterions, especially aromatic counterions, will significantly affect the aggregation and morphological properties of ILs surfactants. In this paper, molecular dynamics (MD) simulations are applied to study the influence of three organic and inorganic counterions (phenolate (PO−), benzoate (BZ−), and Cl−) on the micellar structure of imidazolium (C14mim+) based ILs surfactant in aqueous solutions. Three micelles all possess prolate shape. The PO−, BZ−, and Cl− ions hardly affect the orientation and length of hydrophobic chains in micellar interior. Hydration numbers and average radial density distributions analyses show that interactions between micelles and water molecules are different in studied micelles. Surrounding water molecules penetrate into the deepest region in [C14mim][Cl] micelle. However, adsorbed Cl− ions are mainly located on micellar surface, not penetrating into micellar interior. Due to the intrinsic hydrophobicity of organic ions, both PO− and BZ− ions enter into deeper positions in micelles. Unlike Cl− ions, there exist π-interactions between adsorbed PO− and BZ− ions themselves. One interesting finding is that adsorbed PO− and BZ− ions can make micelle radius (Rg) increase but make solvent accessible surface area (SASA) decrease. Conversely, adsorbed Cl− ions make both Rg and SASA increase. Three MD models for different C14mim+ based micelles are proposed.

A new strategy for extraction of copper cyanide complex ions from cyanide leach solutions by ionic liquids

Copper cyanide complexes in cyanide leach solutions deteriorate the recoveries of gold. Herein, five phosphonate-based [P204]− ionic liquids were synthesized, which were pioneered to apply to extraction of copper cyanide complex ions in cyanide leach solutions. In the extraction process, macroscopic layered solids rich in copper cyanide complex ions were formed at the aqueous-organic phase interface, which was driven by self-assembly of ionic liquids. Notably, the layered solids can be obtained by simple filtration. The extraction behaviors were systematically studied in the present work. The results show that the extraction efficiency in excess of 90 % can be achieved at higher pH (13.16) and enriched as self-assembly solids in the process of one-step extraction and solidification, based on the self-assembly extraction systems of [P4444][P204] IL. It is worthy of note that no self-assembly sample was observed when the extraction systems is applied to extraction zinc and iron cyanide complex ions. It indicates that the present self-assembly extraction systems could be applied in separation copper and zinc/iron cyanide complex ions. Meanwhile, the coordination mechanism was investigated detaily, and the covalent nature played a leading role in the binding interaction. Remarkably, [P4444][P204] can be repeatedly used without obvious loss in extraction capacity of copper cyanide complex ions after two cycles, indicating that the IL has a good recycling ability. In conclusion, it is possible to employ the self-assembly extraction systems to separate and recover various valuable metals from aqueous solutions by designing and developing ILs extractants in the future.

Ionic Liquid/Non-Ionic Surfactant Mixtures As Versatile, Non-Volatile Electrolytes: Double-Layer Capacitance and Conductivity

Self-assembly of ionic liquids (ILs) on 2D materials such as graphene oxide and MXenes facilitated by non-ionic surfactants is a promising approach being increasingly used for the fabrication of high surface area electrodes resulting in high performance supercapacitors. However, the impact that non-ionic surfactants have on double-layer formation and ionic conductivity has yet to be explored. These surfactants are not ionically conductive, have low dielectric constants and high viscosity which are expected to impact the final performance of the electrode. In this study we analyze the effect of adding two commonly used non-ionic surfactants, P123 and Triton X-100 (TX-100) to 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMImTFSI) on the double-layer capacitance formed at a glassy carbon electrode by means of electrochemical impedance spectroscopy. The results, surprisingly suggest an improvement of 75% and 116% in the double layer capacitance measured at the open circuit voltage for 40% of P123 and TX-100, respectively. We also interpret the changes in the DC potential dependence of the capacitance via the most up-to-date understanding of double-layer charging mechanisms with ionic liquids. Similar to previous literature on solvent-based diluents such as polycarbonate and acetonitrile, which cause a similar effect, the improved capacitance is attributed to the reduced Debye length resulting from an increased effective ionic charge accrued by the IL when surrounded by the low-dielectric constant surfactant.Both electrolyte series show the same reduction in ionic conductivity (from 8.5 mS/cm to 1 mS/cm) with respect to concentration regardless of the higher viscosity measured for the P123 electrolyte series. Pulsed field gradient nuclear magnetic resonance, is used to determine the diffusion coefficient for the IL as a function of surfactant concentration and allow us to calculate the effective Stokes radius which is found to shrink significantly as a function of surfactant concentration. Similar to the improved capacitance, this is caused by a reduction in ion-ion interactions and an increase in the average effective charge on each ion. These effects make the electrolyte less sensitive than expected to the increased viscosity caused by addition of the more viscous surfactant phase.The ability to improve the capacitance with non-volatile, low dielectric constant additives, without significantly sacrificing ionic conductivity, opens up an improved avenue for completely non-volatile, non-flammable electrolyte design.

Polymeric surfactant micelle structure modulated by ionic liquids

The very low volatility, high thermal and chemical stability, and broad range of intermolecular interactions that many ionic liquids (ILs) exhibit render them promising as solvents or additives in diverse applications. We are interested in the self-assembly in ionic liquids of amphiphiles, in particular those of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block polymer family, commercially available as Poloxamers or Pluronics. We consider here aqueous solutions of a relatively hydrophobic PEO-PPO-PEO block copolymer (Pluronic P123, EO20PO70EO20) with the representative ionic liquids ethylammonium nitrate (EAN) (protic IL) or 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF4) (aprotic IL). We further compare the effects of ionic liquid electrolytes to those of the classic electrolyte ammonium nitrate (NH4NO3). We report on the block copolymer micelle structure ascertained from analysis of small-angle neutron scattering (SANS) data, and discuss the observed IL effects in the context of the underlying intermolecular interactions. Opposite effects on micelle structure are observed upon addition of EAN or NH4NO3 compared to BmimBF4: an increase in the micelle core radius and association number, and a decrease in the micelle shell thickness indicating dehydration upon addition of EAN or NH4NO3; a decrease in the micelle core radius and association number, and an increase in the shell thickness indicating increased solvation upon addition of BmimBF4. A temperature increase leads to similar effects on the micelle structure as the addition of the kosmotropic electrolytes EAN and NH4NO3. This study for the first time reports PEO-PPO-PEO micelle structure in IL-water mixtures, and utilizes it to proxy the operating intermolecular interactions and the role that ILs play in the self-assembly process.

Permeability of Vesicles for Imidazolium-Based Ionic Liquids in Aqueous Solution: A Molecular Dynamic Simulation Study

Self-assembly of ionic liquids (ILs) in solution has attracted wide attention due to their potential applications in chemical and biological investigations. In this study, the aggregation behavior ...

Uncovering the Underlying Mechanisms Governing the Solidlike Layering of Ionic Liquids (ILs) on Mica.

Significant progress has been made in understanding the IL-solid interface in the past three decades, and a key finding is that ILs can form solidlike layers at the interface. It has been recognized that the electrostatic forces at the solid-IL interface and self-assembly of ILs are key enablers of the IL layering. However, regarding the layering structure of ILs, research from different laboratories is not consistent; i.e., the number of solidlike layers could range from 0 to ∼60, indicating the complexity of the underlying mechanisms and/or the existence of overlooked key parameters. In the current review, we will discuss the underlying mechanisms and key parameters governing the layering of ILs on mica, the most studied model solid. First, we will present the experimental findings from various laboratories, both consistent and contradictory ones, and summarize the current understanding of the governing mechanisms. Then, we will discuss the possible key parameters, including the structure of ILs, surface modification and contamination of mica, and cosolvent impacting the solidlike layering of ILs. Finally, we will discuss future research directions in uncovering the underlying mechanisms.

Soft materials based on colloidal self-assembly in ionic liquids

Ionic liquids (ILs) have attracted much attention as dispersion media for colloidal systems as alternatives to organic solvents and electrolyte solutions. Although colloidal stability is an essential factor for determining the properties and performance of colloidal systems containing ILs, detailed mechanisms for colloidal stabilization have not yet been studied. In the first part of this paper, we highlight our fundamental studies on colloidal stability. Three different repulsive forces, electrostatic, solvation, and steric interactions, are examined for their effectiveness in stabilizing colloidal particles in ILs. In the second part of this report, we provide an overview of our recent studies on colloidal soft materials in the presence of ILs. On the basis of the suspended state of the silica colloid particles, two different soft materials, a colloidal gel and a colloidal glass, were prepared in ILs. Their functional properties, including ionic transport, rheological, and optical properties, are discussed in relation to the microstructures of the colloidal materials. Soft materials based on colloidal self-assembly in ionic liquids: fundamental studies on the colloidal stability in ionic liquids (ILs) are highlighted. Three different repulsive forces—electrostatic, solvation, and steric—are examined for their effectiveness to stabilize colloidal particles in ILs. An overview of recent studies on colloidal soft materials in the presence of ILs is also provided. Based on suspended states of colloid particles, two different soft materials—colloidal gel and colloidal glass—were prepared in ILs. Their functional properties, including ionic transport, rheological and optical properties, are discussed in relation to the microstructures of the colloidal materials.

Ionic liquid-assisted synthesis of highly dispersive bowknot-like ZnO microrods for photocatalytic applications

Here we present a facile method for the preparation of highly dispersive ZnO materials by using ionic liquid 1-methyl-3-[3′-(trimethoxysilyl) propyl] imidazolium chloride as the template. The influence of ionic liquid concentration and calcined atmosphere on the photoactivity is studied. The samples were characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), scanning electron microscope (SEM), N2 gas sorption and ultraviolet-visible diffuse reflectance spectroscopy. The results showed that the as-fabricated ZnO materials consisted of individual microrods with self-assembled bowknot-like architecture whose size was about 1μm. The formation mechanism of the bowknot-like ZnO materials which is based on the self-assembly of ionic liquid is tentatively elucidated. Moreover, the ZnO-2.6N sample exhibited the higher activity for the photodegradation of MB than the photodegradation of MO and RhB. Furthermore, it was found that the ZnO materials calcined under air atmosphere showed the better photocatalytic activities than that of samples calcined under nitrogen atmosphere in the degradation of methylene blue (MB) under UV irradiation. And the special structure, surface area, adsorption capability of dye, the separation rate of photogenerated electron–hole pairs and band gap had effects on the photocatalytic activity of ZnO photocatalysts. O2− was the main active species for the photocatalytic degradation of MB. It is valuable to develop this facile route preparing the highly dispersive bowknot-like ZnO materials and the ZnO materials can be beneficial for environmental protection.

Self-Assembly of Pluronic F127 Diacrylate in Ethylammonium Nitrate: Structure, Rheology, and Ionic Conductivity before and after Photo-Cross-Linking

The self-assembly of an end-functionalized PEO106–PPO70–PEO106 triblock copolymer (BCP) with acrylic end groups (Pluronic F127 diacrylate or FDA) in a protic ionic liquid (deuterated ethylammonium nitrate, dEAN) is studied using small-angle neutron scattering, shear rheology, and dielectric spectroscopy. This functionalization constitutes less than 1 wt % of the copolymer and has no effect on micelle formation in dEAN. The sol–gel transition and the supramolecular crystal structure of the concentrated FDA/dEAN solutions are also found to be unaffected by the acrylation of the end groups. Photo-cross-linking results in viscoelasticity enhancement of the FDA/dEAN solutions with FDA contents below the gel point. Cross-linking gels produces soft elastomers with exceptional elasticity and conductivity comparable to the un-cross-linked solutions. Tuning BCP microstructure via self-assembly in ionic liquids followed by chemical cross-linking is shown to be a promising route for the design of materials with speci...

Self assembly of ionic liquids at the air/water interface

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Triblock Copolymer Self-Assembly in Ionic Liquids: Effect of PEO Block Length on the Self-Assembly of PEO–PPO–PEO in Ethylammonium Nitrate

The microstructure and rheological properties of micellar solutions of Pluronic block copolymers (PEOx–PPOy–PEOx) in deuterated ethylammonium nitrate (dEAN, a protic ionic liquid) are studied by small- and ultrasmall-angle neutron scattering (SANS and USANS), fluorescence microscopy, and shear rheology. A homologous series of three Pluronics with similar PPO block length (F127 (PEO106–PPO70–PEO106), P123 (PEO20–PPO70–PEO20), and L121 (PEO5–PPO70–PEO5)) are examined to explore the effect of the relative balance of solvophilic to solvophobic block size on the self-assembled microstructure. Both F127 and P123 form spherical micelles in dEAN that assemble into face-centered and body-centered cubic supramolecular crystals, respectively, upon increasing concentration or temperature. The transition from disordered to crystalline (ordered) structures manifests as a sol–gel rheological transition. A richer phase diagram is observed in the L121/dEAN system: due to its low solvophilicity in dEAN, L121 self-assembles into structures with low curvatures, namely, vesicles in the dilute regime, elongated (wormlike) micelles at intermediate concentrations and low temperatures, a nematic phase in concentrated solutions, and multilamellar phases at high temperatures. Highly viscoelastic solutions are created by the self-assembly of entangled L121 wormlike micelles. Structural length scales of the three Pluronic/dEAN systems in the various mesophases are determined from SANS and USANS.

Solvent nanostructure, the solvophobic effect and amphiphile self-assembly in ionic liquids

The ability of ionic liquids (ILs) to support amphiphile self-assembly into a range of mesophase structures has been established as a widespread phenomenon. From the ILs evaluated as self-assembly media, the vast majority have supported some lyotropic liquid crystal phase formation. Many neat ionic liquids have been shown to segregate into polar and non-polar domains to form a nanostructured liquid. A very strong correlation between the nanostructure of the ionic liquid and its characteristics as an amphiphile self-assembly solvent has been found. In this review we discuss ionic liquids as amphiphile self-assembly media, and identify trends that can be used to distinguish which ionic liquids are likely to have good promotion properties as self-assembly media. In particular these trends focus on the nanostructure of neat ionic liquids, their solvent cohesive energy density, and the related solvophobic effect. We forecast that many more ILs will be identified as amphiphile self-assembly solvents in the future.

Controlled self-assembly of amphiphiles in ionic liquids and the formation of ionogels by molecular tuning of cohesive energies

In this paper, the self-assembling characteristics of a series of L-glutamate-based ammonium amphiphiles are studied in ionic liquids (ILs). These cationic amphiphiles are dispersible in imidazolium ILs with bis((trifluoromethyl)sulfonyl)amide (TFSA) anion. Amphiphiles-containing didodecyl ester or short dioctyl amide groups were molecularly dispersed in conventional 1-butyl-3-methylimidazolium TFSA, whereas they formed bilayer membranes when they were dispersed in polar, ether linkage-introduced IL. Thus, the modification of ILs exerts a crucial influence on amphiphilic self-assembly. Enhancement of the intermolecular interactions of L-glutamate amphiphiles is achieved by introducing multiple amide bonds and longer alkyl chains, which leads to better self-assembling properties. These amide-enriched amphiphiles form fibrous bilayer assemblies even in conventional ILs with low cohesive energy densities. These observations confirm that the formation of bilayer membranes in ILs is a general phenomenon when the solute molecules have the appropriate ‘ionophilic/ionophobic’ nature. Molecular self-assembly in IL is promoted by controlling cohesive energies of amphiphiles and ILs.

Self-Assembly of Ionic Liquids and Metal Complexes in Super-Cages of NaY: Integration of Free Catalysts and Solvent Molecules into Confined Catalytic Sites

The integration of a free metal complex, Pd(phen) 2+ , and a room temperature ionic liquid (IL) solvent molecule, 1-decyl-3-methyl imidazolium bromide, into a complete catalytically active site and confined in a NaY zeolite super-cage with an appropriate spatial arrangement was investigated. This integration was achieved through a molecular self-assembly method. A preliminary test of this catalyst system for the carbonylation of aniline to methyl phenyl carbamate indicated that far higher catalytic activity could be achieved (TOF increased from 3 000 to 23 000 h −1 ) with far lower amounts of the IL solvent and the Pd complex in comparison with a simple mixture of Pd(phen)Cl 2 /IL/NaY as the catalyst. This new system can also be applied to other areas of catalysis.

High-ion conducting solidified hybrid electrolytes by the self-assembly of ionic liquids and TiO2

We have fabricated solidified electrolytes by using an ionic liquid (BMI TFST) and TiO(2); the electrolyte materials exhibit a high conductivity of 10(-2) S cm(-1) at intermediate temperatures due to self-assembled ionic transport channels.

Morphology evolution of rutile particles from nanorods to microcones, again microspheres via self-assembly in Ionic Liquids (ILs) solution

Morphology evolution of rutile particles from nanorods to microcones, again microspheres were realized with the increasing of TiCl 4 via self-assembly under hydrothermal condition. A kind of ionic liquids, 1-octyl-3-methylimidazole bromide ([C 8mim]Br) was used to assist the fabrication of rutile nanostructures in the system. Characterizations of the products were performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). SEM and TEM micrographs showed that the presence of [C 8mim]Br apparently resulted in the aggregation of rutile particles via self-assembly, till porous structures was formed on the surface of microspheres. Moreover, the microspheres were easy to crack when they were precipitated from solution, and the cracks can be widened under radiation of electron beam, simultaneously accompanied by the exfoliation of rutile whiskers. The corresponding mechanism of self-assembly was proposed to explain the effect of [C 8mim]Br on fabrication of these rutile nanostructures.

Self-Assembly of Ionic Liquid (BMI-PF6)-Stabilized Gold Nanoparticles on a Silicon Surface: Chemical and Structural Aspects

Ultrafine monodisperse gold nanoparticles (AuNPs) were synthesized by an elegant sputtering of gold onto 1- n-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF(6)) ionic liquid. It was found that the BMI-PF(6) supramolecular aggregates were loosely coordinated to the gold nanoparticles and were replaceable with thiol molecules. The self-assembly of BMI-PF(6)-stabilized AuNPs onto a (3-mercaptopropyl)trimethoxysilane (MPS)-functionalized silicon surface in 2D arrays, followed by dodecanethiol (DDT) treatment, have been demonstrated using X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and contact angle measurements. DDT treatment of tethered AuNPs revealed two types of interactions between AuNPs and the MPS-functionalized surface: (a) AuNPs anchor through Au-S chemisorption linkage resulting in strong immobilization and (b) some of the AuNPs are supported by physisorption, driven by BMI-PF(6). The attachment of these particles remains unchanged with sonication. The replacement of BMI-PF(6) aggregates from physisorbed AuNPs with DDT molecules advances the dilution of their interaction with the MPS-functionalized surface, and they subsequently detach from the silicon surface. The present finding is promising for the immobilization of ionic liquid-stabilized nanoparticles, which is very desirable for electronic and catalytic device fabrication. Additionally, these environmentally friendly AuNPs are expected to replace conventional citrate-stabilized AuNPs.