Ion‐Responsive Behavior of Ionic‐Liquid Surfactant Aggregates with Applications in Controlled Release and Emulsification

We propose a simple but efficient, rapid, and quantitative ion‐responsive micelle system based on counter‐anion exchange of a surfactant with an imidazolium unit. The ion‐exchange reaction results in the amphiphilic‐to‐hydrophobic transition of the imidazolium salt, leading to the destruction of the micelles, which has been successfully applied to controlled release and emulsification. The proposed design offers a novel alternative stimulus to control these smart physical aggregates besides pH, temperature and light—with extra advantages. Our finding greatly benefits both fundamental research and industry.     

Ionic‐Liquid‐Assisted Formation of Silver Nanowires

Down to the wire : A simple and effective method to synthesize silver nanowires through an ionic‐liquid‐assisted polyol process is developed (see scheme; scale bar=5 nm). The ionic liquids are tuned to provide the anisotropic growth of silver nanoparticles into nanowires.

     

Structural studies of 1-butyl-3-methylimidazolium tetrafluoroborate/TX-100/ p-xylene ionic liquid microemulsions.

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 (bmimBF(4)), 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.     

Ionic‐Liquid‐Derived,Water‐Soluble Ionic Cellulose

A new type of water‐soluble ionic cellulose was obtained by means of the dissolution of cellulose in dimethylimidazolium methylphosphite at elevated temperatures over 120 °C. FTIR spectroscopy, ¹H and ¹³C NMR spectroscopy, and elemental analysis results revealed that the repeating unit of the water‐soluble cellulose consists of a dialkylimidazolium cation and a phosphite anion bonded to cellulose. The degree of phosphorylation on the cellulose chain was between 0.4 and 1.3 depending on the reaction temperature and time. With an increasing degree of phosphorylation, water solubility was increased. Scanning electron microscopy and X‐ray diffraction analyses revealed that the cellulose crystalline phase in the parent crystalline cellulose changed to an amorphous phase upon transformation into ionic cellulose. Thermogravimetric analysis showed the prepared phosphorylated cellulose was stable over 250 °C and a substantial amount of residue remained at 500 °C.     

Proton/Hydrogen‐Transfer Coordinate of 2,5‐Dihydroxybenzoic Acid Investigated in a Supersonic Beam: Combined IR/UV Spectroscopy in the S0, S1, and D0 States

As a model system for intramolecular proton/hydrogen‐transfer coordinates, the structure of 2,5‐dihydroxybenzoic acid is investigated for the ground, first electronically excited and also the ionic state. Combined IR/UV spectroscopy in molecular‐beam experiments is applied and the experimental results are interpreted by the application of DFT and CASPT2 methods. No proton or hydrogen transfer is observed, but evidence is given for a hydrogen dislocation of the intramolecular hydrogen bond in the S₁ state and to lesser extent in the D₀ state. To obtain direct information on the proton/hydrogen‐transfer coordinate, IR spectra are recorded both in the region of the OH and especially the CO stretching vibrations by also applying two new variants of combined IR/UV spectroscopy for the S₁ and D₀ states. The CO groups are directly involved in the hydrogen bond and, in contrast to the hydrogen‐bonded OH groups, the CO stretching frequencies can be observed in all electronic states.     

Effect of Protic Ionic Liquid and Surfactant Structure on Partitioning of Polyoxyethylene Non‐ionic Surfactants

The partitioning constants and Gibbs free energies of transfer of poly(oxyethylene) n‐alkyl ethers between dodecane and the protic ionic liquids (ILs) ethylammonium nitrate (EAN) and propylammonium nitrate (PAN) are determined. EAN and PAN have a sponge‐like nanostructure that consists of interpenetrating charged and apolar domains. This study reveals that the ILs solvate the hydrophobic and hydrophilic parts of the amphiphiles differently. The ethoxy groups are dissolved in the polar region of both ILs by means of hydrogen bonds. The environment is remarkably water‐like and, as in water, the solubility of the ethoxy groups in EAN decreases on warming, which underscores the critical role of the IL hydrogen‐bond network for solubility. In contrast, amphiphile alkyl chains are not preferentially solvated by the charged or uncharged regions of the ILs. Rather, they experience an average IL composition and, as a result, partitioning from dodecane into the IL increases as the cation alkyl chain is lengthened from ethyl to propyl, because the IL apolar volume fraction increases. Together, these results show that surfactant dissolution in ILs is related to structural compatibility between the head or tail group and the IL nanostructure. Thus, these partitioning studies reveal parameters for the effective molecular design of surfactants in ILs.     

Highly Luminescent and Color‐Tunable Salicylate Ionic Liquids

High quantum yields of up to 40.5 % can be achieved in salicylate‐bearing ionic liquids. A range of these ionic liquids have been synthesized and their photoluminescent properties studied in detail. The differences noted can be related back to the structure of the ionic liquid cation and possible interionic interactions. It is found that shifts of emission, particularly in the pyridinium‐based ionic liquids, can be related to cation–anion pairing interactions. Facile and controlled emission color mixing is demonstrated through combining different ILs, with emission colors ranging from blue to yellow.     

The Microwave‐Assisted Ionic‐Liquid Method: A Promising Methodology in Nanomaterials

In recent years, the microwave‐assisted ionic‐liquid method has been accepted as a promising methodology for the preparation of nanomaterials and cellulose‐based nanocomposites. Applications of this method in the preparation of cellulose‐based nanocomposites comply with the major principles of green chemistry, that is, they use an environmentally friendly method in environmentally preferable solvents to make use of renewable materials. This minireview focuses on the recent development of the synthesis of nanomaterials and cellulose‐based nanocomposites by means of the microwave‐assisted ionic‐liquid method. We first discuss the preparation of nanomaterials including noble metals, metal oxides, complex metal oxides, metal sulfides, and other nanomaterials by means of this method. Then we provide an overview of the synthesis of cellulose‐based nanocomposites by using this method. The emphasis is on the synthesis, microstructure, and properties of nanostructured materials obtained through this methodology. Our recent research on nanomaterials and cellulose‐based nanocomposites by this rapid method is summarized. In addition, the formation mechanisms involved in the microwave‐assisted ionic‐liquid synthesis of nanostructured materials are discussed briefly. Finally, the future perspectives of this methodology in the synthesis of nanostructured materials are proposed.     

Molecular Reorientational Dynamics of the Neat Ionic Liquid 1‐Butyl‐3‐methylimidazolium Hexafluorophosphate by Measurement of 13C Nuclear Magnetic Relaxation Data

The reorientational dynamics of the ionic liquid 1butyl‐3‐methylimidazolium hexafluorophosphate ([BMIM]PF₆) were studied over a wide range of temperatures by measurement of ¹³C spin–lattice relaxation rates and NOE factors. The reorientational dynamics were evaluated by performing fits to the experimental relaxation data. Thus, the overall reorientational motion was described by a Cole–Davidson spectral density with a Vogel–Fulcher–Tammann temperature dependence of the correlation times. The reorientational motion of the butyl chain was modelled by a combination of the latter model for the overall motion with a Bloembergen–Purcell–Pound spectral density and an Arrhenius temperature dependence for the internal motion. Except for C2 in the aromatic ring, an additional reduction of the spectral density by the Lipari–Szabo model had to be employed. This reduction is a consequence of fast molecular motions before the rotational diffusion process becomes effective. The C2 atom did not exhibit this reduction, because the librational motion of the corresponding C2? H vector is severely hindered due to hydrogen bonding with the hexafluorophosphate anion. The observed dynamic features of the [BMIM]⁺ cation confirm quantum‐chemical structures obtained in a former study.     

Aggregation of 2‐Aminobenzimidazole—A Combined Experimental and Theoretical Investigation

An investigation of 2‐aminobenzimidazole was carried out by calculations at HF, MP2, and DFT levels of theory and also by UV and IR spectroscopy. The quantum chemical calculations predict a full shift of the equilibrium towards the amino form, but the absorption spectra in different solvents distinctly show a two‐component equilibrium system. Examination of possible equilibria in solution shows that an equilibrium between two dimeric forms of the amino tautomer of 2‐aminobenzimidazole explains the spectral observations.     

Extraction of Uranium from Aqueous Solutions by Using Ionic Liquid and Supercritical Carbon Dioxide in Conjunction

Super powers! Uranium(VI) ions can be extracted from aqueous solutions into supercritical CO₂ (sc‐CO₂) via an ionic liquid phase that contained tri‐n‐butyl phosphate (TBP) as a complexing agent (see figure). This process has potential applications in the nuclear industry for removing actinides from nuclear waste.

     

The effect of water on the microstructure of 1-butyl-3-methylimidazolium tetrafluoroborate/TX-100/benzene ionic liquid microemulsions

The ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) forms nonaqueous microemulsions with benzene with the aid of nonionic surfactant TX-100. The phase diagram of the ternary system was prepared, and the microstructures of the microemulsion were recognized. On the basis of the phase diagram, a series of ionic liquid-in-oil (IL/O) microemulsions were chosen and characterized by dynamic light scattering (DLS), which shows a similar swelling behavior to typical water-in-oil (W/O) microemulsions. The existence of IL pools in the IL/O microemulsion was confirmed by UV/Vis spectroscopic analysis with CoCl2 and methylene blue (MB) as the absorption probes. A constant polarity of the IL pool is observed, even if small amounts of water are added to the microemulsion, thus suggesting that the water molecules are solubilized in the polar outer shell of the microemulsion, as confirmed by FTIR spectra. 1H NMR spectroscopic analysis shows that these water molecules interact with the electronegative oxygen atoms of the oxyethylene (OE) units of TX-100 through hydrogen-bonding interactions, and the electronegative oxygen atoms of the water molecules attract the electropositive imidazolium rings of [bmim][BF4]. Hence, the water molecules are like a glue that stick the IL and OE units more tightly together and thus make the microemulsion system more stable. Considering the unique solubilization behavior of added water molecules, the IL/O microemulsion system may be used as a medium to prepare porous or hollow nanomaterials by hydrolysis reactions.     

Effect of the Cationic Surfactant Moiety on the Structure of Water Entrapped in Two Catanionic Reverse Micelles Created from Ionic Liquid‐Like Surfactants

The behavior of water entrapped in reverse micelles (RMs) formed by two catanionic ionic liquid‐like surfactants, benzyl‐n‐hexadecyldimethylammonium 1,4‐bis‐2‐ethylhexylsulfosuccinate (AOT‐BHD) and cetyltrimethylammonium 1,4‐bis‐2‐ethylhexylsulfosuccinate (AOT‐CTA), was investigated by using dynamic (DLS) and static (SLS) light scattering, FTIR, and ¹H NMR spectroscopy techniques. To the best of our knowledge, this is the first report in which AOT‐CTA has been used to create RMs and encapsulate water. DLS and SLS results revealed the formation of RMs in benzene and the interaction of water with the RM interface. From FTIR and ¹H NMR spectroscopy data, a difference in the magnitude of the water–catanionic surfactant interaction at the interface is observed. For the AOT‐BHD RMs, a strong water–surfactant interaction can be invoked whereas for AOT‐CTA this interaction seems to be weaker. Consequently, more water molecules interact with the interface in AOT‐BHD RMs with a completely disrupted hydrogen‐bond network, than in AOT‐CTA RMs in which the water structure is partially preserved. We suggest that the benzyl group present in the BHD⁺ moiety in AOT‐BHD is responsible for the behavior of the catanionic interface in comparison with the interface created in AOT‐CTA. These results show that a simple change in the cationic component in the catanionic surfactant promotes remarkable changes in the RMs interface with interesting consequences, in particular when using the systems as nanoreactors.     

Photoinduced Formation of an Azobenzene‐Based CD‐Active Supramolecular Cyclic Dimer

A series of new photo‐responsive amino acid‐derived azobenzenedicarboxylic acid derivatives (S)‐ 1 a – e were synthesized. Compound (S)‐ 1 a in the trans form exhibited no circular dichroism (CD) signal in DMF under ambient conditions, whereas intense Cotton effects were observed upon UV irradiation, indicating the formation of a chiral supramolecular structure in the cis form. The CD signals disappeared when trifluoroacetic acid (TFA) was added to the solution. The ester counterpart [(S)‐ 1 a′ ] showed no CD signal. Hydrogen bonding between the carboxy groups seemed necessary for constructing the supramolecular structure. The kinetic studies of cis to trans isomerization of (S)‐ 1 a demonstrated that the formation of a chiral supramolecule enhances the stability of the cis‐azobenzene structure. The ESI mass spectrum of stilbenedicarboxylic acid (S)‐ 4 , an analogue of (S)‐ 1 b , confirmed the formation of a dimer. A theoretical CD study revealed that (S)‐ 1 a in the cis form should be present as a cyclic chiral dimer.     

Electrochemical and Spectroscopic Study of EuIII and EuII Coordination in the 1-Ethyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquid

Separation processes based on room temperature ionic liquids (RTIL) and electrochemical refining are promising strategies for the recovery of lanthanides from primary ores and electronic waste. However, they require the speciation of dissolved elements to be known with accuracy. In the present study, Eu coordination and Eu^III/Eu^II electrochemical behavior as a function of water content in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm][NTf₂]) was investigated using UV–visible spectrophotometry, time-resolved laser fluorescence spectroscopy, electrochemistry, and X-ray absorption spectroscopy. In situ measurements were performed in spectroelectrochemical cells. Under anhydrous conditions, Eu^III and Eu^II were complexed by NTf₂, forming Eu−O and Eu−(N,O) bonds with the anion sulfoxide function and N atoms, respectively. This complexation resulted in a greater stability of Eu^II, and in quasi-reversible oxidation–reduction with an E₀’ potential of 0.18 V versus the ferrocenium/ferrocene (Fc⁺/Fc) couple. Upon increasing water content, progressive incorporation of water in the Eu^III coordination sphere occurred. This led to reversible oxidation–reduction reactions, but also to a decrease in stability of the +II oxidation state (E₀’=−0.45 V vs. Fc⁺/Fc in RTIL containing 1300 mm water).