The confinement and anion type effect on the physicochemical properties of ionic liquid/halloysite nanoclay ionogels

This work is the first attempt to study the physicochemical properties of ionogels - quasi-solid hybrid materials formed by ionic liquids (ILs) − 1-butyl-3-methylimidazolium (BMIm⁺) salts with dicyanamide- (DCA⁻), bis(trifluoromethylsulfonyl)imide- (TFSI⁻), and trifluoromethanesulfonate- (Otf⁻) anions - and halloysite, a powdered clay filler with nanotube particles (at the IL:Hal molar ratio of 2:1) in order to find possible new applications of ionic liquids and industrial minerals. The electron microscopy, TG, and DSC analysis, FTIR spectroscopy, X-ray diffraction analysis, conductometry and cyclic voltammetry methods are used to investigate the anion effect on the IL interaction with halloysite. It has, for the first time, been found that the distinguishing feature of halloysite interaction with an IL determining the structural changes in the clay mineral and electrochemical characteristics of the ionogels is partial dehydration of the clay and absorption of the released water by the ionic liquid. It is shown that the halloysite dehydration effect depends on the IL hydrophilicity determined by the anion type, corresponds to the series: BMImDCA > BMImOtf > BMImTFSI. The electrochemical and thermal behaviour of ILs confined within a halloysite matrix differs from that of bulk ILs and is controlled by the anion type. Temperature dependences of the structural resistance of the halloysite filler are radically different for the ILs with high and low hydrophilicity. The effects resulting from the formation of halloysite-based ionogels can be of interest to those who develop quasi-solid ionic conductors that can work within a wide temperature range.     

Overview of Ionogels in Flexible Electronics

Ionogels have aroused wide interests in the field of flexible electronics. The combination of solid‐state networks and ionic liquids opens up thousands of possibilities for ionogels. The unique structures of ionogels endow them excellent mechanical properties, conductivity and thermal stability to approach the challenge of flexible electronic. A large number of new ionogels have been developed by different methods including the exchange of solution, polymeric ionic liquid and in‐situ reactions in ionic liquids (gelation of low molecular weight gelators, self‐assembly of block polymers, formation of double‐network structure, ionogel nanocomposites and direct polymerization of polymerizable monomers). The aim of this review is to discuss different preparation methods of ionogels and the comparison of their advantages.     

聚合物离子凝胶的研究进展

聚合物离子凝胶由聚合物网络封装离子液体而构成,通过调节离子液体和聚合物网络的特性,使其不仅具有高离子电导率、不可燃性和热、化学和电化学稳定性,而且具有高柔韧性和力学性能,近年来在离子皮肤、软机器人和柔性可穿戴系统等领域发展迅速。本文对近三年来聚合物基离子凝胶的结构设计特点、性能特性及其发展现状进行综述,分析和评述了聚合物结构对离子凝胶功能的影响机制,并对聚合物离子凝胶的未来发展进行了展望。     

Ionogels: Squeeze flow rheology and ionic conductivity of quasi-solidified nanostructured hybrid materials containing ionic liquids immobilized on halloysite

Ionogels are hybrid ion-conducting materials consisting of ionic liquids stabilized by inorganic or polymer fillers and having good prospects for application in solid-state and flexible electronics and energy storage devices. The work presents the results of studying the rheological properties and ionic conductivity of a series of ionogels based on halloysite nanoclay and bis(trifluoromethylsulfonyl)imide ionic liquids with EMIm⁺, BMIm⁺, BM₂Im⁺, BMPyrr⁺, BMPip⁺ and MOc₃Am⁺ cations and content of the dispersion phase of 43–48%. The obtained values are compared with the analogous characteristics of bulk ionic liquids. It has been established that the IL cation structural characteristics affect the viscoplastic properties of ionogels subjected to uniaxial quasistatic compression (20 °C), ionic conductivity and structural resistance coefficient of an inorganic filler (from ?20 to +80 °C). Additive models of conductivity in binary systems are applied to obtain correlations linking ionic conductivity of ionogels with that of pure ionic liquids.     

Poly(dimethylsiloxane)‐Supported Ionogels with a High Ionic Liquid Loading

The immiscibility of poly(dimethylsiloxane) (PDMS) and ionic liquids (ILs) was overcome to create PDMS‐supported IL gels (ionogels) with IL loadings of up to 80 % by mass through a simple sol–gel reaction at room temperature. By stirring a mixture of a functionalized PDMS oligomer, formic acid, and an IL (or lithium‐in‐IL solution), a resin was formed that could be cast to create a freestanding, flexible ionogel. PDMS‐supported ionogels exhibited favorable ionic conductivity (ca. 3 mS cm^?1) and excellent mechanical behavior (elastic modulus: ca. 60 kPa; fatigue life: >5000 cycles; mechanically stable at temperatures up to 200 °C). The activation energy of ionic conductivity was shown to be nearly identical for the ionogel and the neat IL, in contrast to ionogel systems wherein the scaffold material is miscible with the IL. This similarity indicates that IL/scaffold chemical interactions are key to the understanding of ionogel electrical performance, especially at elevated temperatures.     

Ionogels, ionic liquid based hybrid materials

The current interest in ionic liquids (ILs) is motivated by some unique properties, such as negligible vapour pressure, thermal stability and non-flammability, combined with high ionic conductivity and wide electrochemical stability window. However, for material applications, there is a challenging need for immobilizing ILs in solid devices, while keeping their specific properties. In this critical review, ionogels are presented as a new class of hybrid materials, in which the properties of the IL are hybridized with those of another component, which may be organic (low molecular weight gelator, (bio)polymer), inorganic (e.g. carbon nanotubes, silica etc.) or hybrid organic-inorganic (e.g. polymer and inorganic fillers). Actually, ILs act as structuring media during the formation of inorganic ionogels, their intrinsic organization and physicochemical properties influencing the building of the solid host network. Conversely, some effects of confinement can modify some properties of the guest IL, even though liquid-like dynamics and ion mobility are preserved. Ionogels, which keep the main properties of ILs except outflow, while allowing easy shaping, considerably enlarge the array of applications of ILs. Thus, they form a promising family of solid electrolyte membranes, which gives access to all-solid devices, a topical industrial challenge in domains such as lithium batteries, fuel cells and dye-sensitized solar cells. Replacing conventional media, organic solvents in lithium batteries or water in proton-exchange-membrane fuel cells (PEMFC), by low-vapour-pressure and non flammable ILs presents major advantages such as improved safety and a higher operating temperature range. Implementation of ILs in separation techniques, where they benefit from huge advantages as well, relies again on the development of supported IL membranes such as ionogels. Moreover, functionalization of ionogels can be achieved both by incorporation of organic functions in the solid matrix, and by encapsulation of molecular species (from metal complexes to enzymes) in the immobilized IL phase, which opens new routes for designing advanced materials, especially (bio)catalytic membranes, sensors and drug release systems (194 references).     

Low density ionogels obtained by rapid gellification of tetraethyl orthosilane assisted by ionic liquids

A non-hydrolytic one pot sol-gel method has been used to synthesize mesoporous silica ionogels with the confined ionic liquid (IL) 1-ethyl 3-methyl imidazolium tetra fluoro-borate [EMIM][BF(4)]. The precursor for obtaining the SiO(2) matrix was tetraethyl orthosilicate (TEOS) and formic acid was used as a catalyst. These ionogels have been characterized by density measurements, TEM, BET, DSC, TGA and FTIR. The incorporation of the ionic liquid [EMIM][BF(4)] enhances the gellification rate which results in the ionogels having very low density (~0.3 g cm(-3)). The low density has been explained on the basis of the creation of 'blind embedded pores' in the matrix (apart from open pores) due to very rapid gellification (~1 min). Morphological studies provide experimental evidence for the presence of blind pores/voids inside the ionogel ingots. We have also shown that the IL entrapped in nanopores (~7-8 nm pore size) of the SiO(2) matrix has different physical properties than the bulk IL viz. (a) the phase transition temperatures (T(g), T(c) and T(m)) of the IL change upon confinement, (b) the thermal stability reduces upon confinement, and (c) the pore wall interaction with the IL results in changes in the C-H vibrations of the imidazolium ring and alkyl chain (the former increasing) which is also indicated in our DFT-calculation.     

Ionogels of a Sugar Surfactant in Ionic Liquids

Green and environmentally friendly ionogels formed by a sugar surfactant were prepared in two kinds of imidazolium‐based ionic liquids. The phase transition from ribbon structures to lamellar structures induced by temperature and the transition mechanism were investigated in detail by means of freeze‐fracture TEM and field‐emission SEM observations, as well as small‐angle X‐ray scattering measurements. The rheological properties and tribological properties of two kinds of ionogels were systematically investigated. The difference in the lubricating properties and antiwear capability can be explained well by the mechanical and viscoelastic properties, as well as the different microstructures of samples destroyed by shear forces. This work provides a better understanding of the relationship between the structures, rheological properties, and tribological properties of ionogels.     

In Situ Synthesis of Imidazolium‐Crosslinked Ionogels via Debus–Radziszewski Reaction Based on PAMAM Dendrimers in Imidazolium Ionic liquid

This study reports a remarkably facile method to synthesize novel ionogels with imidazolium cycle crosslinks based on polyamidoamine (PAMAM) dendrimers via one‐pot, modified Debus–Radziszewski reaction in ionic liquid 1‐ethyl‐3‐methylimidazolium acetate ([EMIM][OAc]). High room temperature ionic conductivity (up to 6.8 mS cm⁻¹) is achieved, and more remarkably, it can still exceed 1 mS cm⁻¹ when the dendrimer content reached 70% because PAMAM dendrimers are completely amorphous with many cavities and the newly formed imidazolium crosslinks contains ions. The elastic modulus of these ionogels can exceed 10⁶ Pa due to the newly‐formed rigid imidazolium crosslinks. Crucially, these ionogels are robust gels even at temperatures up to 160 °C. Such novel ionogels with high ionic conductivity, tunable modulus, and flexibility are desirable for use in high‐temperature flexible electrochemical devices.     

Mixed solvents for cellulose derivatization under homogeneous conditions: kinetic,spectroscopic, and theoretical studies on the acetylation of the biopolymer in binary mixtures of an ionic liquid and molecular solvents

Rate constants for the acetylation of microcrystalline cellulose (MCC), by ethanoic anhydride in the presence of increasing concentrations of the ionic liquid (IL), 1-allyl-3-methylimidazolium chloride in dipolar aprotic solvents (DAS), N,N-dimethylacetamide (DMAC), and acetonitrile (MeCN), have been calculated from conductivity data. The third order rate constants showed a linear dependence on [IL]. We explain this result by assuming that the reacting cellulose is hydrogen-bonded to the IL. This is corroborated by kinetic data of the acetylation of cyclohexylmethanol, FTIR of the latter compound and of cellobiose in mixtures of IL/DAS, and conductivity of the binary solvent mixtures in absence, and presence of MCC. Cellulose acetylation is faster in IL/DMAC than in IL/MeCN; this difference is explained based on solvatochromic data (empirical polarity and basicity) and molecular dynamics simulations. Results of the latter indicate hydrogen-bond formation between the hydroxyl groups of the anhydroglucose unit of MCC, (Cl^?) of the IL, and the dipole of the DMAC. Under identical experimental conditions, acetylation in IL/DMAC is faster than that in LiCl/DMAC (2.7–8 times), due to differences in the enthalpies and entropies of activation.     

Ionogels encompassing ionic liquid with liquid like performance preferable for fast solid state electrochromic devices

Novel ionogels encompassing an ionic liquid encaged in an inorganic matrix were synthesized by sol–gel chemistry. The ability of these highly conducting ionogels (∼10⁻² S cm⁻¹ at 25 °C) to act as liquid electrolytes in spite of their solid form has been exploited in inorganic electrochromic devices based on tungsten oxide and Prussian blue electrodes. These devices exhibit extremely fast switching kinetics and make it the best and only candidate for the realization of fast all solid state electrochromic devices.     

N-methyl-2-pyrrolidonium-based Brönsted-Lewis acidic ionic liquids as catalysts for the hydrolysis of cellulose

We experimentally studied the catalytic performances of a series of Br?nsted-Lewis acidic N-methyl-2-pyrrolidonium metal chlorides([Hnmp]Cl/MCl_x, where M=Fe, Zn, Al, or Cu) for the hydrolysis of microcrystalline cellulose(MCC) and cotton to produce reducing sugar. A variety of factors, such as temperature, time, ionic liquid(IL) species, IL dosage, and the concentration of the metal chloride were investigated. [Hnmp]Cl/FeCl_3 presented the best hydrolysis performance, affording a 98.8% yield of total reducing sugar from MCC(1 h, 100 °C, 0.1 g MCC, 0.2 g acidic IL, 2.0 g [Bmim]Cl as solvent), which is better than or comparable to results previously obtained with other –SO_3H functionalized acidic ILs. The hydrolysis performances of [Hnmp]Cl/MClx were rationalized using density functional theory calculations, which indicated that interactions between the metal chlorides and the cellulose, including charge-transfer interactions are important in the hydrolysis of cellulose and degradation of glucose. This work shows that Br?nsted-Lewis acidic ILs are potential catalysts for the hydrolysis of cellulose to produce sugar.     

Facile preparation of regenerated cellulose film from cotton linter using organic electrolyte solution (OES)

Regenerated cellulose (RC) film is an important cellulose-based product with a wide range of applications in the packaging industry and drug delivery. In this study, RC film was prepared using an organic electrolyte solution (OES)/ionic liquid (IL) system consisting of 1-ethyl-3-methylimidazolium acetate (EmimAc) and dimethyl sulfoxide (DMSO) to dissolve cotton linter at room temperature. Results showed that OES with EmimAc molar fraction in the range from 0.2 to 0.4 could rapidly dissolve cotton linter at room temperature, in contrast to 80 °C for EmimAc solution (control). The cellulose degradation was therefore much less than for the control, resulting in significant improvement in the mechanical properties and thermal stability of the RC film. In addition, the presence of DMSO significantly decreased the viscosity of the cellulose/OES system, being advantageous for casting of the RC film.     

[AEIM]Cl的合成及微波溶解微晶纤维素

以氯丙烯和N-乙基咪唑为原料合成了离子液体氯化1-烯丙基-3-乙基-咪唑盐([AEIM]Cl),利用FT-IR和¹HNMR对其化学结构进行了表征。采用微波加热法溶解微晶纤维素(MCC),考察 [AEIM]Cl对纤维素的溶解性能。研究了NaOH、微波和高压等3种预处理方式对微晶纤维素的相对结晶度、聚合度及溶解率的影响。利用FT-IR、XRD、TGA和SEM分别对溶解后得到的再生纤维素的化学结构、晶型变化、热稳定性及表观形貌进行测试与分析。结果表明,合成的离子液体是目标产物,对微晶纤维素表现出很好的溶解能力,且高温高压条件下15％的NaOH水溶液对微晶纤维素处理后,得到的纤维素相对结晶度最小,聚合度最低,溶解率最高。溶解过程中纤维素没有发生衍生化反应,溶解后得到的再生纤维素的相对结晶度和微晶尺寸变小,热稳定性降低。     

Luminescent Hybrid Ionogels Functionalized with rare Earth fluoride Up‐conversion Nanocrystals Dispersing in Ionic Liquid

Rare earth doped fluorides (BaMgF₄, aYF₄ and BaYF₅/BaLuF₅) have been synthesized and dispersed in an ionic liquid compound, (3‐triethoxysilyl) propyl‐3‐methylimidazolium chloride (denoted as IM⁺Cl ^? ). Through the cohydrolysis and copolycondensatoin reaction between the alkoxy group (3‐triethoxysilyl) of IM⁺ and tetraethoxysilane in the presence of carboxylic acids (formic acid) as catalyst and water source, luminescent hybrid ionogels form subsequently. ¹H NMR spectroscopy, X‐ray diffraction, transmission electron microscopy, scanning electron microscopy and especially up‐conversion (UC) luminescence spectroscopy are used to characterize the precursors and the resulted hybrid ionogels. These hybrid ionogels exhibit the UC luminescence properties of immobilized rare earth fluoride nanocrystals (BaMgF₄, NaYF₄ and BaYF₅/BaLuF₅) doped Er³⁺/Tm³⁺, Yb³⁺.     

A route to heat resistant solid membranes with performances of liquid electrolytes

The confinement of ionic liquids within a porous silica matrix was performed by a one-step non-hydrolytic sol-gel route, leading to hybrid materials (called "ionogels") featuring both the mechanical and transparency properties of silica gels and the high ionic conductivity and thermal stability of ionic liquids.     

A functionalised ionic liquid: 1-(3-chloro-2-hydroxypropyl)-3-methyl imidazolium chloride

An ionic liquid (IL) containing an appended 3-chloro-2-hydroxypropyl functionality group 1-(3-chloro-2-hydroxypropyl)-3-methyl imidazolium chloride was synthesised by the reaction of N-methyl imidazole, hydrochloric acid and epichlorohydrin. The ionic liquid showed reasonably high conductivity and heat stability up to 230°C. Its structures were characterised by FT-IR, ¹H NMR and ¹³C NMR spectra. The physical characteristics of the ionic liquid, such as conductivity and solvation abilities have been investigated. Due to its high polarity, the IL is able to dissolve many inorganic salts, and due to hydroxyl-rich microenvironment, it is able to dissolve cellulose go up to 10 (wt%). The ILs can be used for synthesising other ILs or polyelectrolyte.     

Effect of microcrystalline and nanocrystals cellulose fillers in materials based on PLA matrix

The aim of this work was to compare the effects of microcrystalline cellulose (MCC) and cellulose nanocrystals (CNC) addition on the properties of PLA matrix. The CNC were obtained by acid hydrolysis of the MCC. Both MCC and CNC were separately incorporated in PLA at ratios of 3, 5 and 7 wt%. In some compositions, organophilic silica (R972) was added to improve the cellulose-matrix compatibility. The properties of the materials were evaluated by FTIR, XRD, NMR and mechanical tests. Functional groups and crystalline structure of MCC and CNC were determined by FTIR and XRD, respectively. NMR T₁H values showed that films containing CNC presented better interfacial interaction than those containing MCC, and indicated that R972 acts as compatibilizer. MCC and CNC acted as nucleating agents for PLA crystallization and there was an improvement in the mechanical performance of materials with the addition of CNC.     

Blend films of natural wool and cellulose prepared from an ionic liquid

Natural wool/cellulose blends were prepared in an ionic liquid green solvent, 1-butyl-3-methylimidazolium chloride (BMIMCl) and the films were formed subsequently from the coagulated solutions. The wool/cellulose blend films show significant improvement in thermal stability compared to the coagulated wool and cellulose. Moreover, the blend films exhibited an increasing trend of tensile strength with increase in cellulose content in the blends which could be used for the development of wool-based materials with improved mechanical properties, and the elongations of the blends were considerably improved with respect to the coagulated films of wool and cellulose. It was found that there was hydrogen bonding interaction between hydroxyl groups of wool and cellulose in the coagulated wool/cellulose blends as determined by Fourier transform infrared (FTIR) spectroscopy. The ionic liquid was completely recycled with high yield and purity after the blend film was prepared. This work presents a green processing route for development of novel renewable blended materials from natural resource with improved properties.     

A facile one-step way for extraction of nanocellulose with high yield by ball milling with ionic liquid

93.1% yield of nanocellulose was successfully extracted from cellulose powder (CP) by planetary ball milling in the presence of ionic liquid (IL) of 1-butyl-3-methylimidazolium chloride (BMIMCl). The morphology of nanofibrillated cellulose present in fibrous network with 10–25 nm in diameter and micrometer scale in length and the chemical composition and crystal structure were maintained as cellulose type I. At 600 °C degradation temperature, the residue amount of the obtained nanocellulose was about 55% more that of CP, implying it had higher thermal stability. The used BMIMCl was recovered and reused at least 4 times. The nanocellulose obtained by using the recovered IL also demonstrated the same properties as those from the fresh one. For comparison, another kind of IL of 1-ethyl-3-methylimidazolium acetate (EMIMOAc) was also used in this study. It is found that the ball milling of cellulose in the presence of IL is an effective and environmental friendly way for the production of nanocellulose with high yield.