Multifunctional Magnetoelectric Sensing and Bending Actuator Response of Polymer-Based Hybrid Materials with Magnetic Ionic Liquids.

With the evolution of the digital society, the demand for miniaturized multifunctional devices has been increasing, particularly for sensors and actuators. These technological translators allow successful interaction between the physical and digital worlds. In particular, the development of smart materials with magnetoelectric (ME) properties, capable of wirelessly generating electrical signals in response to external magnetic fields, represents a suitable approach for the development of magnetic field sensors and actuators due to their ME coupling, flexibility, robustness and easy fabrication, compatible with additive manufacturing technologies. This work demonstrates the suitability of magnetoelectric (ME) responsive materials based on the magnetic ionic liquid (MIL) 1-butyl-3-methylimidazolium tetrachloroferrate ([Bmim][FeCl4]) and the polymer poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE) for magnetic sensing and actuation device development. The developed sensor works in the AC magnetic field and has frequency-dependent sensitivity. The materials show voltage responses in the mV range, suitable for the development of magnetic field sensors with a highest sensitivity (s) of 76 mV·Oe-1. The high ME response (maximum ME voltage coefficient of 15 V·cm-1·Oe-1) and magnetic bending actuation (2.1 mm) capability are explained by the magnetoionic (MI) interaction and the morphology of the composites.

Diarylethene-Based Ionic Liquids: Synthesis and Photo-Driven Solution Properties.

In this work, the design and synthesis of a series of photochromic gemini diarylethene-based ionic liquids (GDILs) with different cationic motifs is reported. Several synthetic pathways were optimized for the formation of cationic GDILs with chloride as the counterion. The different cationic motifs were achieved through the N-alkylation of the photochromic organic core unit with different tertiary amines, including different aromatic amines such as imidazole derivatives and pyridinium, and other non-aromatic amines. These novel salts present surprising water solubility with unexplored photochromic features that broaden their known applications. The covalent attachment of the different side groups dictates their water solubility and differences upon photocyclization. The physicochemical properties of GDILs in aqueous and in imidazolium-based ionic liquid (IL) solutions were investigated. Upon irradiation with ultraviolet (UV) light, we have observed changes in the physico-chemical properties of distinct solutions containing these GDILs, at very low concentrations. More specifically, in aqueous solution, the overall conductivity increased with the time of UV photoirradiation. In contrast, in IL solution, these photoinducible changes are dependent on the type of ionic liquid used. These compounds can improve non-ionic and ionic liquids' solutions since we can change their properties, such as conductivity, viscosity or ionicity, only by UV photoirradiation. The electronic and conformational changes associated with these innovative stimuli GDILs may open new opportunities for their use as photoswitchable materials.

Ionic Liquids as Biocompatible Antibacterial Agents: A Case Study on Structure-Related Bioactivity on Escherichia coli.

The potential of ionic liquids (ILs) to be used as antimicrobial agents for biomedical applications has been hindered by the fact that most of them are cytotoxic toward mammalian cells. Understanding the mechanism of bacterial and mammalian cellular damage of ILs is key to their safety design. In this work, we evaluate the antimicrobial activity and mode of action of several ILs with varying anions and cations toward the clinically relevant Gram-negative Escherichia coli. Langmuir monolayer technique was used to evaluate if the IL's mode of action was related to the bacterial cell membrane interaction for an effective E. coli killing. 1-Decyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide [DMIM][TFSI] and trihexyltetradecyl phosphonium bis(trifluoromethylsulfonyl) imide [P6,6,6,14][TFSI] were surface-active and induced bacterial cell lysis, through a membrane-disruption phenomenon on bacteria, in a mechanism that was clearly related to the long alkyl chains of the cation. 1-Ethyl-3-methylimidazolium hydrogen sulfate [EMIM][HSO4] was highly antimicrobial toward E. coli and found suitable for biological applications since it was harmless to mammalian cells at most of the tested concentrations. The results suggest that the imidazolium cation of the ILs is mostly responsible not only for their antimicrobial activity but also for their cytotoxicity, and the inclusion of different anions may tailor the ILs' biocompatibility without losing the capacity to kill bacteria, as is the case of [EMIM][HSO4]. Importantly, this IL was found to be highly antimicrobial even when incorporated in a polymeric matrix.

Prediction of the Phase Composition Profile of Three-Compound Mixtures in Liquid-Liquid Equilibrium: A Chemoinformatics Approach.

Machine-learning models were developed to predict the composition profile of a three-compound mixture in liquid-liquid equilibrium (LLE), given the global composition at certain temperature and pressure. A chemoinformatics approach was explored, based on the MOLMAP technology to encode molecules and mixtures. The chemical systems involved an ionic liquid (IL) and two organic molecules. Two complementary models have been optimized for the IL-rich and IL-poor phases. The two global optimized models are highly accurate, and were validated with independent test sets, where combinations of molecule1+molecule2+IL are different from those in the training set. These results highlight the MOLMAP encoding scheme, based on atomic properties to train models that learn relationships between features of complex multi-component chemical systems and their profile of phase compositions.

Effect of Thiouronium-Based Ionic Liquids on the Formation and Growth of CO2 (sI) and THF (sII) Hydrates.

In this manuscript, two thiouronium-based ionic liquids (ILs), namely 2-ethylthiouronium bromide [C2th][Br] and 2-(hydroxyethyl)thiouronium bromide [C2OHth][Br], were tested at different concentrations (1 and 10 wt%) for their ability to affect CO2 (sI) and tetrahydrofuran (THF) (sII) hydrate formation and growth. Two different methods were selected to perform a thermodynamic and kinetic screening of the CO2 hydrates using a rocking cell apparatus: (i) an isochoric pressure search method to map the hydrate phase behavior and (ii) a constant ramping method to obtain the hydrate formation and dissociation onset temperatures. A THF hydrate crystal growth method was also used to determine the effectiveness of the ILs in altering the growth of type sII hydrates at atmospheric pressure. Hydrate-liquid-vapor equilibrium measurements revealed that both ILs act as thermodynamic inhibitors at 10 wt% and suppress the CO2 hydrate equilibria ~1.2 °C. The constant ramping methodology provides interesting results and reveals that [C2OHth][Br] suppresses the nucleation onset temperature and delays the decomposition onset temperatures of CO2 hydrates at 1 wt%, whereas suppression by [C2th][Br] was not statistically significant. Normalized pressure plots indicate that the presence of the ILs slowed down the growth as well as the decomposition rates of CO2 hydrates due to the lower quantity of hydrate formed in the presence of 1 wt% ILs. The ILs were also found to be effective in inhibiting the growth of type sII THF hydrates without affecting their morphology. Therefore, the studied thiouronium ILs can be used as potential dual-function hydrate inhibitors. This work also emphasizes the importance of the methods and conditions used to screen an additive for altering hydrate formation and growth.

Improvement of New Dianionic Ionic Liquids vs Monoanionic in Solubility of Poorly Water-Soluble Drugs.

New ionic liquids (ILs) based on dianionic phosphonate anions and ammonium cations were prepared and characterized. They were used as excipients to increase the water solubility of two oral drugs, piroxicam and ibuprofen, that are slightly soluble in water. An increment in solubility of 300-fold was achieved for ibuprofen when compared with pure water, with only 0.25 mol% of IL in water. Interestingly, this was achieved with the less toxic dianionic ionic liquid [N4 1 2OH 2OH]2 [C2H5PO3], which presents an IC50 of 120 mM (≈0.25 mol%). On the other hand, piroxicam showed an increase of 480-fold for the same dianionic ionic liquid, with the same ionic liquid percentage. In contrast, for monoanionic ionic liquids, the effect was not so pronounced, and only a 10-fold was obtained, in the presence of 0.3 mol% of IL. The lipophilicity (logP) of drugs decreased in the presence of these ILs. Cytotoxicity profile of these ILs was determined and they did not show a significant impact towards healthy fibroblasts. The cytotoxicity of ibuprofen and piroxicam was also determined, and cellular viability almost did not change when ionic liquid was in the presence of 1 mM of oral drug.

Paramagnetic Ionic Liquid/Metal Organic Framework Composites for CO2/CH4 and CO2/N2 Separations.

Global warming is arguably the biggest scientific challenge of the twenty-first century and its environmental consequences are already noticeable. To mitigate the emissions of greenhouse gases, particularly of CO2, there is an urgent need to design materials with improved adsorbent properties. Five different magnetic ionic liquids were impregnated into the metal-organic framework ZIF-8. The composites were produced by a direct-contact method, and their performance as sorbents for gas separation applications was studied. The impact of the ionic liquid anion on the sorption capacity and ideal CO2/CH4 and CO2/N2 selectivities were studied, focusing on understanding the influence of metal atom and ligand on the adsorbent properties. Reproducible methodology, along with rigorous characterization, were established to assess the impact of the ionic liquid on the performance of the composite materials. Results show that the ionic liquid was well-impregnated, and the ZIF-8 structure was maintained after ionic liquid impregnation. The produced composites were of microporous nature and were thermally stable. CO2, CH4, and N2 adsorption-desorption isotherms were obtained at 303 K and between 0 and 16 bar. The adsorption-desorption data of the composites were compared with that obtained for original ZIF-8. The general trend in composites is that the increased gas uptake per available pore volume compensates the pore volume loss. Adsorption data per unit mass showed that composites have reversible sorption, but inferior gas uptake at all pressure ranges. This is due to the observed total pore volume loss by the ionic liquid pore occupation/blockage. In most cases, composites showed superior selectivity performance at all pressure range. In particular, the composite [C4MIM]2[MnCl4]@ZIF-8 shows a different low-pressure selectivity trend from the original MOF, with a 33% increase in the CO2/N2 selectivity at 1 bar and 19% increase in the CO2/CH4 selectivity at 10 bar. This material shows potential for use in a post-combustion CO2 capture application that can contribute to greenhouse gas mitigation.

Design of Ionic-Liquid-Based Hybrid Polymer Materials with a Magnetoactive and Electroactive Multifunctional Response.

Multifunctional materials with sensor and actuator capabilities play an increasing role in modern technology. In this scope, hybrid materials with magnetic sensing and an electromechanical actuator response based on magnetic ionic liquids (MILs) and the polymer poly(vinylidene fluoride) (PVDF) have been developed. MILs comprising different cation alkyl chain lengths [Cnmim]+ and sharing the same anion [FeCl4]- were incorporated at 20 wt % into the PVDF matrix and the morphological, physical, chemical, and functional properties of the materials were evaluated. An increasing IL alkyl chain length leads to the formation of a porous structure, together with an increase in the electroactive PVDF ß-phase content of the polymer and a decrease in the crystallinity degree and thermal stability. The magnetic susceptibility of the [Cnmim][FeCl4]/PVDF films reveals a paramagnetic behavior. The multifunctional response is characterized by a magnetoionic response that decreases with increasing IL alkyl chain length, the highest magnetoionic coefficient (1.06 ± 0.015 V cm-1 Oe-1) being observed for [C2mim][FeCl4]/PVDF. The electromechanical actuator response is characterized by a highest displacement of 1.1 mm for the [C4mim][FeCl4]/PVDF film by applying a voltage of 4 V at a frequency of 100 mHz. Further, their solution processing makes these multiresponsive materials compatible with additive manufacturing technologies.

Simultaneous Separation of Antioxidants and Carbohydrates From Food Wastes Using Aqueous Biphasic Systems Formed by Cholinium-Derived Ionic Liquids.

The food industry produces significant amounts of waste, many of them rich in valuable compounds that could be recovered and reused in the framework of circular economy. The development of sustainable and cost-effective technologies to recover these value added compounds will contribute to a significant decrease of the environmental footprint and economic burden of this industry sector. Accordingly, in this work, aqueous biphasic systems (ABS) composed of cholinium-derived bistriflimide ionic liquids (ILs) and carbohydrates were investigated as an alternative process to simultaneously separate and recover antioxidants and carbohydrates from food waste. Aiming at improving the biocompatible character of the studied ILs and proposed process, cholinium-derived bistriflimide ILs were chosen, which were properly designed by playing with the cation alkyl side chain and the number of functional groups attached to the cation to be able to create ABS with carbohydrates. These ILs were characterized by cytotoxicity assays toward human intestinal epithelial cells (Caco-2 cell line), demonstrating to have a significantly lower toxicity than other well-known and commonly used fluorinated ILs. The capability of these ILs to form ABS with a series of carbohydrates, namely monosaccharides, disaccharides and polyols, was then appraised by the determination of the respective ternary liquid-liquid phase diagrams at 25°C. The studied ABS were finally used to separate carbohydrates and antioxidants from real food waste samples, using an expired vanilla pudding as an example. With the studied systems, the separation of the two products occurs in one-step, where carbohydrates are enriched in the carbohydrate-rich phase and antioxidants are mainly present in the IL-rich phase. Extraction efficiencies of carbohydrates ranging between 89 and 92% to the carbohydrate-rich phase, and antioxidant relative activities ranging between 65 and 75% in the IL-rich phase were obtained. Furthermore, antioxidants from the IL-rich phase were recovered by solid-phase extraction, and the IL was recycled for two more times with no losses on the ABS separation performance. Overall, the obtained results show that the investigated ABS are promising platforms to simultaneously separate carbohydrates and antioxidants from real food waste samples, and could be used in further related applications foreseeing industrial food waste valorization.

Anomalous and Not-So-Common Behavior in Common Ionic Liquids and Ionic Liquid-Containing Systems.

This work highlights unexpected, not so well known responses of ionic liquids and ionic liquid-containing systems, which are reported in a collective manner, as a short review. Examples include: (i) Minima in the temperature dependence of the isobaric thermal expansion coefficient of some ILs; (ii) Viscosity Minima in binary mixtures of IL + Molecular solvents; (iii) Anomalies in the surface tension within a family of ILs; (iv) The constancy among IL substitution of Cp/Vm at and around room temperature; (v) ILs as glass forming liquids; (vi) Alternate odd-even side alkyl chain length effects; (vii) Absolute negative pressures in ILs and IL-containing systems; (viii) Reversed-charged ionic liquid pairs; (ix) LCST immiscibility behavior in IL + solvent systems.

Ionic-Liquid-Based Printable Materials for Thermochromic and Thermoresistive Applications.

Smart materials exhibiting thermochromic and themoresistive properties based on the electroactive polymer poly(vinylidene fluoride) (PVDF) and the ionic liquid (IL) bis(1-butyl-3-methylimidazolium) tetrachloronickelate ([Bmim]2[NiCl4]) have been developed with different contents of [Bmim]2[NiCl4] (10, 20, and 40 wt %) within the polymer matrix. The morphology of the composites is studied, and the thermochromic and thermoresistive properties are evaluated. Independently of the IL content, the PVDF/[Bmim]2[NiCl4] composites present a porous morphology and thermochromic response, revealed by the color change of the composites from transparent to dark blue, attributed to the tetrahedral complex NiCl42- formed after a dehydration process. Further, the electrical conductivity increases with increasing IL content and decreases with increasing temperature. It is also shown that the incorporation of the IL into the PVDF matrix leads to an increase in the electroactive ß phase and a decrease in the degree of crystallinity and thermal stability with increasing [Bmim]2[NiCl4] content. The printability and applicability of the developed materials as sensors are also demonstrated.

Enhancement of water solubility of poorly water-soluble drugs by new biocompatible N-acetyl amino acid N-alkyl cholinium-based ionic liquids.

The major challenge of the pharmaceutical industry is to find potential solvents for poorly water-soluble drug molecules. Ionic liquids (ILs) have attracted this industry as (co-) solvents due to their unique physicochemical and biological properties. Herein, a straightforward approach for the enhancement of the water solubility of paracetamol and sodium diclofenac is presented, using new biocompatible N-acetyl amino acid N-alkyl cholinium-based ionic liquids as co-solvents (0.2-1 mol%). These new ionic liquids were able to increase the water solubility of these drugs up to four times that in pure water or in an inorganic salt solution. In the presence of these ILs, the drugs lipophilicity (log P was not significantly changed for paracetamol, but for sodium diclofenac it was possible to decrease significantly its lipophilicity. Concerning cytotoxicity in human dermal fibroblasts it was observed that ILs did not show a significant toxicity, and were able to improve cell viability compared with the respective precursors.

Odd-even effect on the formation of aqueous biphasic systems formed by 1-alkyl-3-methylimidazolium chloride ionic liquids and salts.

This work provides a comprehensive evaluation of the effect of the cation alkyl side chain length of the 1-alkyl-3-methylimidazolium chloride series ([C n C1im]Cl, n = 2-14) of ionic liquids (ILs) on their capability to form aqueous biphasic systems (ABSs) with salts and self-aggregation derived properties. The liquid-liquid phase behavior of ternary systems composed of [C n C1im]Cl, water, and K3PO4 or K2CO3 and the respective Setschenow salting-out coefficients (ks ), a quantitative measure of the two-phase formation ability, were determined. An odd-even effect in the ks values along the number of methylene groups of the longest IL cation alkyl side chain was identified for the ABS formed by K2CO3, a weaker salting-out agent where the phenomenon is clearly identified. In general, cations with even alkyl side chains, being likely to display higher molar volumes, are more easily salted-out and thus more prone to undergo phase separation. The odd-even effect in the ks values is, however, more significant in ILs up to n = 6, where the nanostructuration/nanosegregation of ILs plays a less relevant role. Still, with the [C n C1im]Cl (n = 7-14) series of ILs, an odd-even effect was also identified in the ILs' ionization degree, molar conductivity, and conductivity at infinite dilution. In summary, it is shown here that the ILs' odd-even effect occurs in IL aqueous solutions and not just in neat ILs, an already well-established phenomenon occurring in a series of ILs' properties described as a result of the orientation of the terminal methyl groups to the imidazolium ring cation and consequent effect in the ILs' cohesive energy.

Low-field giant magneto-ionic response in polymer-based nanocomposites.

The future of magnetoelectric (ME) materials is closely linked to the optimization of the ME response on nanocomposites or to the introduction of new effects to achieve higher ME performance from low magnetic fields. Here, we report a P(VDF-TrFE)/[C4mim][FeCl4] nanocomposite with a magneto-ionic response that produces giant magnetoelectric coefficients up to ≈10 V cm-1 Oe-1. This response comprises a magnetically triggered ionic/charge movement within the porous structure of the polymer, being this a novel phenomenon never experimentally observed or explored in magnetoelectric composites. This work successfully demonstrates the concept of exploring magnetic ionic liquids, such as [C4mim][FeCl4], in polymer-based magnetoelectric nanocomposites, suitable for low-field magnetic sensing devices. Such nanocomposites have remarkable potential for applications, not only because they exhibit a high ME response with scalable production and with good reproducibility but also because this coupling between magnetic order and electric order via ionic effects can lead to additional novel effects.

Molecular dynamics studies on the structure and interactions of ionic liquids containing amino-acid anions.

Several molecular dynamics (MD) simulations have been performed in order to obtain structural information on ionic liquids (ILs) based on amino-acid anions. Six hydrophilic ILs containing cholinium or imidazolium cations combined with alaninate, glycinate or lysinate anions were modelled using the all-atom CL&P and OPLS-AA force fields. Both pure ILs and their aqueous solutions have been studied. The MD data have allowed us to analyse structure factors, S(q), and pair radial distributions functions, g(r), as well as aggregation patterns and specific interactions. The results have shown us that in neat amino-acid-based ILs the anions interact mainly through their carboxylate moiety with the charged centres of the cations. Both the lack of heavy atoms and the small size of the interacting centre in the anion contribute to the absence of a charge ordering peak in the structure factor functions of the corresponding ILs. In turn, their aqueous solutions reveal the existence of small ionic aggregates. The size distribution of these aggregates is strongly dependent on the solution's concentration. This fact points to the possibility of using amino-acid-based ILs as agents to promote hydrotrope effects, significant for the solubilisation and stabilization of organic molecules and macromolecules in aqueous solution.

ILs through the looking glass: electrostatics and structure probed using charge-inverted ionic liquid pairs.

Ionic liquids combining potassium cations with 1-alkyl-3-methylcyclopentadienyl anions, K[CnC1Cp] (n = 4, 6) have been synthesized. Differential scanning calorimetry measurements have shown that K[C4C1Cp] and K[C6C1Cp] melt without decomposition at around 90 °C. These two ionic liquids are the charge-inverted counterparts of [C4C1Im]Cl and [C6C1Im]Cl, two common ionic liquids. The concept of charge-inverted ionic pairs is used to explore the nature of the interactions and structure in different ionic compounds, from simple alkali halide salts to ionic liquids based on complex molecular ions. Different sets of experimental data, empirical correlations and molecular dynamics simulations are used to that effect.

Polycyclic aromatic hydrocarbons as model solutes for carbon nanomaterials in ionic liquids.

The aim of this work is to understand the details of the interactions of ionic liquids with carbon nanomaterials (graphene and nanotubes) using polyaromatic compounds as model solutes. We have combined the measurements of thermodynamic quantities of solvation with molecular dynamics simulations to provide a microscopic view. The solubility of five polycyclic aromatic hydrocarbons (naphthalene, anthracene, phenanthrene, pyrene and coronene) was determined in seven ionic liquids ([C4C1im][C(CN)3], [C4C1pyrr][Ntf2], [C10C1im][Ntf2], [C2C1im][C(CN)3], [C2C1im][Ntf2], [C3C1pyrr][N(CN)2] and [C4C1im][N(CN)2]) at 298 K. The enthalpies of the dissolution of naphthalene, anthracene and pyrene were measured in four of the ionic liquids. Free energies were estimated from those measurements in order to analyse the entropic or enthalpic contributions to the dissolution process. Molecular dynamics simulations provided solvation free energies that were compared to experimental and structural information. Spatial distributions of solvent ions around the solutes when combined with IR measurements elucidate the structure of solvation environments. Interactions between the imidazolium rings of cations and the π system of the solutes have been identified. However, ionic liquids with pyrrolidinium cations appeared as better solvents due to favourable enthalpic contributions compared to imidazolium cations. Long alkyl side chains on cations lead to higher solubility and lower enthalpy of dissolution by creating a "softer" solvation environment. Considering the effect of anions, small and planar anions lead to higher solubilities and lower enthalpies of dissolution of polyaromatic hydrocarbons. These findings provide the design principles based on molecular interactions and the structure of solvation environments to choose or formulate ionic liquids in view of their affinity for carbon nanomaterials.

Protonic Ammonium Nitrate Ionic Liquids and Their Mixtures: Insights into Their Thermophysical Behavior.

This study is centered on the thermophysical characterization of different families of alkylammonium nitrate ionic liquids and their binary mixtures, namely the determination at atmospheric pressure of densities, electric conductivities and viscosities in the 288.15 < T/K < 353.15 range. First, measurements focusing on ethylammonium, propylammonium and butylammonium nitrate systems, and their binary mixtures, were determined. These were followed by studies involving binary mixtures composed of ethylammonium nitrate (with three hydrogen bond donor groups) and different homologous ionic liquids with differing numbers of hydrogen bond donor groups: diethylammonium nitrate (two hydrogen bond donors), triethylammonium nitrate (one hydrogen bond donor) and tetraethylammonium nitrate (no hydrogen bond donors). Finally, the behavior of mixtures with different numbers of equivalent carbon atoms in the alkylammonium cations was analyzed. The results show a quasi-ideal behavior for all monoalkylammonium nitrate mixtures. In contrast, the other mixtures show deviations from ideality, namely when the difference in the number of carbon atoms present in the cations increases or the number of hydrogen bond donors present in the cation decreases. Overall, the results clearly show that, besides the length and distribution of alkyl chains present in a cation such as alkylammonium, there are other structural and interaction parameters that influence the thermophysical properties of both pure compounds and their mixtures.

Organocatalyzed One-Step Synthesis of Functionalized N-Alkyl-Pyridinium Salts from Biomass Derived 5-Hydroxymethylfurfural.

An efficient and scalable method has been developed for the synthesis of N-alkylpyridinium salts from biomass derived 5-hydroxymethylfurfural and alkyl amines using a catalytic amount of formic acid. This protocol is also extended to various diamines providing the exclusive formation of mono-N-alkylpyridinium salts. In addition, the mechanism for the formation of pyridinium salts was studied by DFT and using H2(18)O isotope labeled experiments showing no incorporation of (18)O in the product.

Spontaneous emulsification in ionic liquid/water systems and its use for templating of solids.

We report on the spontaneous formation of nano-sized ionic liquid/water (IL/W) emulsions in a simple system solely composed of an IL and aqueous solution of an inorganic salt. The IL ions play a dual role, that of both a surfactant and the dispersed phase. No extra surfactant is needed to promote emulsification. Droplets generation at the IL/W interface is captured by nanoparticulate and porous films that imprint the morphology of this unstable interface. The emulsion droplets are employed to create core-shell microcrystals with potential functionality.