Efficient method for in situ agitation of liquids directly inside NMR spectrometer.

The objective of the method is to allow agitation and fast homogenization of liquid systems in NMR tubes, directly inside the NMR spectrometer. The setup makes it possible to record spectra of samples that are macroscopically not stable, as dispersions of large particles. It makes also possible to fasten the homogeneization of liquid during a reaction or a phase transition. In the present paper, the method has been evaluated using homogeneous liquid extraction (HLLE). This configuration can also be used to introduce gases in different systems to perform various types of experiments. The set up consists in a Teflon tube inserted in the NMR tube bringing gas that yields agitation by bubbling. The gas flow is tuned using an electronically operated valve connected to gas line and to the NMR console. The method details how to reach proper homogenization without any perturbation, as liquid leaks.•An easy method for agitation of liquids inside NMR spectrometers.•The set up can be used for the insertion of gases in the NMR tube inside the spectrometer.•The method allows the study of the mixing of biphasic systems by NMR techniques.

Synthesis of Purine-Based Ionic Liquids and Their Applications.

Bio-based ionic liquids (ILs) are being increasingly sought after, as they are more sustainable and eco-friendly. Purines are the most widely distributed, naturally occurring N-heterocycles, but their low water-solubility limits their application. In this work, four purines (theobromine, theophylline, xanthine, and uric acid) were combined with the cation tetrabutylammonium to synthesize bio-based ILs. The physico-chemical properties of the purine-based ILs were characterized, including their melting and decomposition temperatures and water-solubility. The ecotoxicity against the microalgae Raphidocelis subcapitata was also determined. The ILs show good thermal stability (>457 K) and an aqueous solubility enhancement ranging from 53- to 870-fold, in comparison to their respective purine percursors, unlocking new prospects for their application where aqueous solutions are demanded. The ecotoxicity of these ILs seems to be dominated by the cation, and it is similar to chloride-based IL, emphasizing that the use of natural anions does not necessarily translate to more benign ILs. The application of the novel ILs in the formation of aqueous biphasic systems (ABS), and as solubility enhancers, was also evaluated. The ILs were able to form ABS with sodium sulfate and tripotassium citrate salts. The development of thermoresponsive ABS, using sodium sulfate as a salting-out agent, was accomplished, with the ILs having different thermosensitivities. In addition, the purine-based ILs acted as solubility enhancers of ferulic acid in aqueous solution.

Organisation of clay nanoplatelets in a polyelectrolyte-based hydrogel.

We investigate the organisation of clay nanoplatelets within a hydrogel based on modified ionenes, cationic polyelectrolytes forming physically crosslinked hydrogels induced by hydrogen bonding and π-π stacking. Combination of small angle X-ray and neutron scattering (SAXS, SANS) reveals the structure of the polyelectrolyte network as well as the organisation of the clay additives. The clay-free hydrogel network features a characteristic mesh-size between 20 and 30 nm, depending on the polyelectrolyte concentration. Clay nanoplatelets inside the hydrogel organise in a regular face-to-face stacking manner, with a large repeat distance, following rather closely the hydrogel mesh-size. The presence of the nanoplatelets does not modify the hydrogel mesh size. Further, the clay-compensating counterions (Na+, Ca2+ or La3+) and the clay type (montmorillonite, beidellite) both have a significant influence on nanoplatelet organisation. The degree of nanoplatelet ordering in the hydrogel is very sensitive to the negative charge location on the clay platelet (different for each clay type). Increased nanoplatelet ordering leads to an improvement of the elastic properties of the hydrogel. On the contrary, the presence of dense clay aggregates (tactoids), induced by multi-valent clay counterions, destroys the hydrogel network as seen by the reduction of the elastic modulus of the hydrogel.

Aggregation of Plate-like Colloids Induced by Charged Polymer Chains: Organization at the Nanometer Scale Tuned by Polymer Charge Density.

We study the aggregation of charged plate-like colloids, Na-montmorillonite clays, in the presence of ionenes, oppositely charged polymer chains. The choice of the charged polymer allows tuning its linear charge density to match/mismatch the average charge separation on the clay surfaces. We assess the nanoscale structure of the aggregates formed by small-angle X-ray and neutron scattering. The nanoscale features of the formed clay aggregates are dominated by the presence of a stacking peak, giving clear evidence for the formation of clay tactoids, that is, a face-to-face aggregation geometry of the clay platelets. The chain charge density of ionenes influences not only the stacking repeat distance within the clay tactoids but also the extent of stacking and abundance of the tactoids. We may distinguish two regimes as a function of clay and ionene polymer charge densities (ρc and ρp, respectively). The first regime applies to ρp > ρc and ρp ≈ ρc, that is, for highly and "matching" charged chains. Under these conditions, the intercalated chains lie in a flat conformation within the tactoids, irrespective of the ionic strength (within the range studied, i.e., up to 0.05 M NaBr). For weakly charged chains, ρp < ρc, undulation of the ionene chains within the tactoid is seen. The degree of undulation increases with ionic strength due to the decreasing persistence length of the ionene chains. The extent of stacking (5-10 platelets per tactoid) is a general feature of all the systems, and its origin remains unknown. The system corresponding to the closest match in charge separations on the clay surface and on the polymer chain (ρp ≈ ρc) features the highest abundance of tactoids. This coincides with the highest macroscopic density as deduced from simple visual inspection of sediment volumes. This leads to the open question regarding the link between the density at the nanoscale and the macroscopic density and sedimentation behavior of the aggregate.

Structural and Morphological Description of Sn/SnOx Core-Shell Nanoparticles Synthesized and Isolated from Ionic Liquid.

The potential application of high capacity Sn-based electrode materials for energy storage, particularly in rechargeable batteries, has led to extensive research activities. In this scope, the development of an innovative synthesis route allowing to downsize particles to the nanoscale is of particular interest owing to the ability of such nanomaterial to better accommodate volume changes upon electrochemical reactions. Here, we report on the use of room temperature ionic liquid (i.e., [EMIm+][TFSI-]) as solvent, template, and stabilizer for Sn-based nanoparticles. In such a media, we observed, using Cryo-TEM, that pure Sn nanoparticles can be stabilized. Further washing steps are, however, mandatory to remove residual ionic liquid. It is shown that the washing steps are accompanied by the partial oxidation of the surface, leading to a core-shell structured Sn/SnOx composite. To understand the structural features of such a complex architecture, HRTEM, Mössbauer spectroscopy, and the pair distribution function were employed to reveal a crystallized ß-Sn core and a SnO and SnO2 amorphous shell. The proportion of oxidized phases increases with the final washing step with water, which appeared necessary to remove not only salts but also the final surface impurities made of the cationic moieties of the ionic liquid. This work highlights the strong oxidation reactivity of Sn-based nanoparticles, which needs to be taken into account when evaluating their electrochemical properties.

Concentrated assemblies of magnetic nanoparticles in ionic liquids.

Maghemite (γ-Fe2O3) nanoparticles (NPs) can be successfully dispersed in a protic ionic liquid, ethylammonium nitrate (EAN), by transfer from aqueous dispersions into EAN. As the aqueous systems are well controlled, several parameters can be tuned. Their crucial role towards the interparticle potential and the structure of the dispersions is evidenced: (i) the size of the NPs tunes the interparticle attraction monitoring dispersions to be either monophasic or gas-liquid-like phase separated; (ii) the nature of the initial counterion in water (here sodium, lithium or ethylammonium) and the amount of added water (<20 vol%) modulate the interparticle repulsion. Very concentrated dispersions with a volume fraction of around 25% are obtained thanks to the gas-liquid-like phase separations. Such conclusions are derived from a fine structural and dynamical study of the dispersions on a large range of spatial scales by coupling several techniques: chemical analyses, optical microscopy, dynamic light scattering, magneto-optic birefringence and small angle scattering.

Synthesis of tin nanocrystals in room temperature ionic liquids.

The aim of this work was to investigate the synthesis of tin nanoparticles (NPs) or tin/carbon composites, in room temperature ionic liquids (RTILs), that could be used as structured anode materials for Li-ion batteries. An innovative route for the synthesis of Sn nanoparticles in such media is successfully developed. Compositions, structures, sizes and morphologies of NPs were characterized by high-energy X-ray diffraction (HEXRD), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). Our findings indicated that (i) metallic tetragonal ß-Sn was obtained and (ii) the particle size could be tailored by tuning the nature of the RTILs, leading to nano-sized spherical particles with a diameter ranging from 3 to 10 nm depending on synthesis conditions. In order to investigate carbon composite materials for Li-ion batteries, Sn nanoparticles were successfully deposited on the surface of multi-wall carbon nanotubes (MWCNT). Moreover, electrochemical properties have been studied in relation to a structural study of the nanocomposites. The poor electrochemical performances as a negative electrode in Li-ion batteries is due to a significant amount of RTIL trapped within the pores of the nanotubes as revealed by XPS investigations. This dramatically affected the gravimetric capacity of the composites and limited the diffusion of lithium. The findings of this work however offer valuable insights into the exciting possibilities for synthesis of novel nano-sized particles and/or alloys (e.g. Sn-Cu, Sn-Co, Sn-Ni, etc.) and the importance of carbon morphology in metal pulverization during the alloying/dealloying process as well as prevention of ionic liquid trapping.

Potential of long chain ionic liquids for on-line sample concentration techniques: application to micelle to solvent stacking.

The performance of micelle to solvent stacking (MSS) in capillary zone electrophoresis (CZE) was improved for anionic analytes using the long chain ionic liquid type cationic surfactant 1-dodecyl-3-methylimidazolium tetrafluoroborate (C12-MIM-BF4). The peak heights and corrected peak areas of the test profens and herbicides were enhanced up to 59 and 110-fold, respectively when compared to typical injection. These were up to 10 times better compared to the surfactant cetyltrimethyl ammonium bromide as MSS carrier. This performance was attributed to the properties of C12-MIM-BF4. MSS requires micelles in the sample for transport of bound analytes to a stacking boundary that contains an organic solvent for effective electrophoretic mobility reversal. The ionic liquid micelles provided better analyte transport properties that resulted from its hydrophobic and pi-pi interaction capabilities. The good solubility of the ionic liquid in high percentages of organic solvent also facilitated a more effective reversal of mobility. The LODs obtained for the test analytes were from 0.06 to 0.12 µg/mL. The linearity R² values in terms of peak height and corrected area were ≥ 0.99. The interday repeatabilities (%RSD, n=10,) were 0.5-2.2% for retention time, 1.9-4.7% for corrected areas and 4.1-6.4% for peak heights.

Redox-switched amphiphilic ionic liquid behavior in aqueous solution.

A new redox amphiphilic ionic liquid (AIL) containing ferrocene as a redox-active group was synthesized, 1-(11-ferrocenylundecyl)-3-methylimidazolium bromide (Fc11MIm+). Adsorption and aggregation of both reduced and oxidized forms of this ferrocenated AIL in aqueous solution were studied by surface tension measurements. The micellization was favored for the reduced ferrocenated AIL (Fc11MIm+) as compared with the oxidized ferrocenated AIL (Fc+11MIm+). Minimum areas at the air/aqueous solution interface were identical whereas limiting surface tensions were slightly different. This corroborated the formation of an expanded monolayer of redox active AIL at the interface. The electrochemical behavior of redox active AIL was investigated. The electrochemical responses of Fc11MIm+ aqueous solution interestingly differed, depending on its concentration. Below the cmc, the electrochemical reaction was dominated by ferrocenated AIL adsorbed onto the electrode surface; then above the cmc, it was controlled by the Fc11MIm+ diffusing to the electrode. For the latter, the electrochemical mechanism was suggested to couple with the disruption reaction of the reduced form micelles.

Determination of aqueous inclusion complexation constants and stoichiometry of alkyl(methyl)-methylimidazolium-based ionic liquid cations and neutral cyclodextrins by affinity capillary electrophoresis.

Affinity CE (ACE) method was developed to characterize the complex formation between seven alkyl(methyl)methylimidazolium-based ionic liquid (IL) cations and eight neutral cyclodextrins (CD). The effective mobility data of the IL cations were processed according to classical nonlinear and linear treatments to obtain the complex stoichiometry and formation constant K. The majority of systems followed a 1:1 complexation stoichiometry model but in four cases a 1:2 stoichiometry was better satisfied. The K values obtained for each IL were compared to elucidate the main influences of IL and CD nature. The availability of these data should lend support to various application areas, including the screening and tailoring of new interactions in the solution for CE.

Ion transfer processes at ionic liquid based redox active drop deposited on an electrode surface.

Ion transfer across the boundary formed at an ionic liquid drop deposited on an electrode immersed in aqueous solution, generated by electrochemical redox reaction at the electrode-ionic liquid interface, is studied to obtain information about the ability of anions to be transferred into a room temperature ionic liquid.

Behaviour of a binary solvent mixture constituted by an amphiphilic ionic liquid, 1-decyl-3-methylimidazolium bromide and water Potentiometric and conductimetric studies.

We investigated the properties of 1-decyl-3-methylimidazolium bromide (DMImBr), a molten salt at room temperature, and its mixtures with water in the whole proportions. At low concentrations, this salt behaved like a classical cationic amphiphile. Its critical micellar concentration (cmc) was determined by conductimetry and by measuring electromotive forces (EMF) with bromide or cationic surfactant-selective electrodes. Moreover, the association rate of the counter ion to micelle has been determined on a wide range of concentrations, allowing characterising the micellisation equilibrium by a solubility product. The conductivity of this liquid electrolyte in mixtures with water was maximal at high concentrations. We modelled this behaviour, taking into account the molar volume fraction of both phases. Our results show that these solutions, which are composed of dispersed aggregates, behave like mixtures of two phases that interpenetrate themselves.

Membrane electrodes sensitive to doubly charged surfactants. Application to a cationic gemini surfactant.

The response of a membrane electrode is not always identical to that of a redox electrode. Indeed, in the case of membrane electrode the response is not due to a redox equilibrium but to a cross-membrane potential. So, the membrane electrode's response depends mainly on the carrier system and the nature of the membrane. The properties of the membrane can favour several reactions giving rise to different ionic species diffusing in the membrane. The expression of the cross-membrane potential thus depends on the number and quantities of these ionic species. To illustrate this, we established the equations for the case of a two-charge cation detected by a univalent charged carrier. We show that the Nernstian response is not applicable to membrane electrodes. This approach allowed us to interpret results obtained with a cationic gemini surfactant-selective electrode prepared in the laboratory. To prove the well working of this electrode, we determined the critical micelle concentration in water and several NaBr solutions (0.004, 0.006, 0.01 and 0.02 M) from which the counterion binding has been determined.