Quantized Friction across Ionic Liquid Thin Films

Ionic liquids, salts in the liquid state under ambient conditions, are of great interest as precision lubricants. Ionic liquids form layered structures at surfaces, yet it is not clear how this nano-structure relates to their lubrication properties. We measured the friction force between atomically smooth solid surfaces across ionic liquid films of controlled thickness in terms of the number of ion layers. Multiple friction-load regimes emerge, each corresponding to a different number of ion layers in the film. In contrast to molecular liquids, the friction coefficients differ for each layer due to their varying composition

Dynamics in Quaternary Ionic Liquids with Non-Flexible Anions: Insights from Mechanical Spectroscopy

The present work investigates how mechanical properties and ion dynamics in ionic liquids (ILs) can be affected by ILs’ design while considering possible relationships between different mechanical and transport properties. Specifically, we study mechanical properties of quaternary ionic liquids with rigid anions by means of Dynamical Mechanical Analysis (DMA). We are able to relate the DMA results to the rheological and transport properties provided by viscosity, conductivity, and diffusion coefficient measurements. A good agreement is found in the temperature dependence of different variables described by the Vogel−Fulcher−Tammann model. In particular, the mechanical spectra of all the measured liquids showed the occurrence of a relaxation, for which the analysis suggested its attribution to a diffusive process, which becomes evident when the ion dynamics are not affected by the fast structural reorganization of flexible anions on a local level

Energy and environmental analysis of flavonoids extraction from bark using alternative solvents

[EN] Tree barks are rich in extractive compounds, among which the flavonoids are considered as products of interest. Due to the increase in the demand for these natural products, the development of efficient and sustainable extraction processes is needed. This work aimed to study the selective extraction of flavonoids from Larix decidua bark using an environmentally friendly process. For this purpose, different extraction techniques as well as different solvents were used in order to achieve the highest flavonoid content. The characterisation results revealed improvements in extraction yield not only with the use of intensification processes, but also with the use of ionic liquids as solvents with a proven selectivity for flavonoids. [C4C1im]Br and [C4C1im][BF4] considerably improved the total flavonoid content in comparison with the other extraction methods. The antioxidant capacities of all the extracts obtained were very high, confirming their potential for different applications. The [C4C1im]Br (25 wt%) was selected as the best solvent not only because of its good flavonoid extraction ability, but also because of the good antioxidant properties of the extract, and simultaneous microwave-ultrasound assisted extraction was the most energy saving process.This research was financially supported by the Basque Government (scholarship of young researchers training of Leyre Sillero and project IT1008-16). Leyre Sillero would like to acknowledge the support received from the Imperial College London during her stay

Effect of the cation structure on the properties of homobaric imidazolium ionic liquids

In this work we investigate the structure-property relationships in a series of alkylimidazolium ionic liquids with almost identical molecular weight. Using a combination of theoretical calculations and experimental measurements, we have shown that re-arranging the alkyl side chain or adding functional groups results in quite distinct features in the resultant ILs. The synthesised ILs, although structurally very similar, cover a wide spectrum of properties ranging from highly fluid, glass forming liquids to high melting point crystalline salts. Theoretical ab initio calculations provide insight on minimum energy orientations for the cations, which then are compared to experimental X-ray crystallography measurements to extract information on hydrogen bonding and to verify our understanding of the studied structures. Molecular dynamics simulations of the simplest (core) ionic liquids are used in order to help us interpret our experimental results and understand better why methylation of C^{2} position of the imidazolium ring results in ILs with such different properties compared to their non-methylated analogues

Process analysis of ionic liquid-based blends as H2S absorbents: search for thermodynamic/kinetic synergies

Acid gas absorption by ionic liquids (ILs) has arisen as a promising alternative technique for biogas or natural gas upgrading. In the present work, IL-based blends are evaluated for potential thermodynamic/kinetic synergistic effects on hydrogen sulfide (H2S) capture through physical and/or chemical absorption. First, a molecular simulation analysis by means of COSMO-RS was used to select IL-based blends with enhanced H2S absorbent thermodynamic properties. Physical absorption parameters of reference (KHenry) for H2S in several IL-based blends were calculated at 298 K, involving both IL mixtures and conventional industrial absorbents (tetraglyme (TGM)) with ILs at different compositions. A Henry's constant deviation parameter (ΔHKHenryH2S) was employed to analyze the nonideal effects of the mixture on H2S gas solubility in IL-based blends. In addition, the viscosities and diffusivities of the IL-based blends were estimated as key parameters controlling H2S diffusion and absorbent uptake rates. From this analysis, a sample of IL-based blends with promising thermodynamic and kinetic properties was selected for H2S physical absorption. A process simulation analysis using the COSMO-based/Aspen Plus methodology was then carried out and the selected absorbents were evaluated by modeling H2S capture in an industrial-scale commercial packed column. One IL, 1-butyl-3-methylimidazoium acetate ([Bmim][OAc]), presenting high H2S chemical absorption and a low viscous industrial solvent (TGM) were also included. The strong kinetic control of H2S capture by physical absorption indicated the limited potential performance of IL-based blends or neat ILs in industrial equipment. In contrast, the COSMO/Aspen analysis revealed that adequate formulations based on [Bmim][OAc] and TGM present enhanced H2S absorbent properties compared to the neat compounds. These computational results may be used to guide future experimental research to design new H2S absorbents, reducing the highly demanding experimental inputFinancial support from Ministerio de Economía y Competitividad of Spain (project CTQ2017-89441-R) and Comunidad de Madrid (project P2018/EMT4348) is acknowledge

Occupational Health and Safety Issues in Ontario Sawmills and Veneer/Plywood Plants: A Pilot Study

A pilot study was conducted within the Ontario sawmill and veneer/plywood manufacturing industry. Information was collected by postal questionnaire and observational walk-through surveys. Industrial hygiene walk-through surveys were conducted at 22 work sites, and measurements for wood dust, noise, and bioaerosol were taken. The aim of the study was to obtain data on the current status regarding health and safety characteristics and an estimate of wood dust, noise, and bioaerosol exposures. The occupational exposure to wood dust and noise are similar to what has been reported in this industry in Canada and elsewhere. Airborne wood dust concentration ranged between 0.001 mg/m3 and 4.87 mg/m3 as total dust and noise exposure ranged between 55 and 117 dB(A). The study indicates the need for a more comprehensive industry-wide study of wood dust, noise, and bioaersols

Room temperature ionic liquids with two symmetric ions

Room temperature ionic liquids typically contain asymmetric organic cations. The asymmetry is thought to enhance disorder, thereby providing an entropic counter-balance to the strong, enthalpic, ionic interactions, and leading, therefore, to lower melting points. Unfortunately, the synthesis and purification of such asymmetric cations is typically more demanding. Here we introduce novel room temperature ionic liquids in which both cation and anion are formally symmetric. The chemical basis for this unprecedented behaviour is the incorporation of ether-containing side chains – which increase the configurational entropy – in the cation. Molecular dynamics simulations indicate that the ether-containing side chains transiently sample curled configurations. Our results contradict the long-standing paradigm that at least one asymmetric ion is required for ionic liquids to be molten at room temperature, and hence open up new and simpler design pathways for these remarkable materials

Ether functionalisation, ion conformation and the optimisation of macroscopic properties in ionic liquids

Ionic liquids are an attractive material class due to their wide liquid range, intrinsic ionic conductivity, and high chemical as well as electrochemical stability. However, the widespread use of ionic liquids is hindered by significantly higher viscosities compared to conventional molecular solvents. In this work, we show how the transport properties of ionic liquids can be altered significantly, even for isostructural ions that have the same backbone. To this end, structure–property relationships have been determined for a set of 16 systematically varied representative ionic liquids. Variations in molecular structure include ammonium vs. phosphonium, ether vs. alkyl side chains, and rigid vs. flexible anions. Ab initio calculations are used to relate molecular structures to the thermal, structural and transport properties of the ionic liquids. We find that the differences in properties of ether and alkyl functionalised ionic liquids are primarily dependent on minimum energy geometries, with the conformational flexibility of ether side chains appearing to be of secondary importance. We also show unprecedented correlations between anion conformational flexibility and transport properties. Critically, increasing fluidity upon consecutive introduction of ether side chains and phosphonium centres into the cation is found to be dependent on whether the anion is flexible or rigid. We demonstrate that targeted design of functional groups based on structure–property relationships can yield ionic liquids of exceptionally high fluidity

Dynamics, cation conformation and rotamers in guanidinium ionic liquids with ether groups

Ionic liquids are modern materials with a broad range of applications, including electrochemical devices, the exploitation of sustainable resources and chemical processing. Expanding the chemical space to include novel ion classes allows for the elucidation of novel structure-property relationships and fine tuning for specific applications. We prepared a set of ionic liquids based on the sparsely investigated pentamethyl guanidinium cation with a 2-ethoxy-ethyl side chain in combination with a series of frequently used anions. The resulting properties are compared to a cation with a pentyl side chain lacking ether functionalization. We measured the thermal transitions and transport properties to estimate the performance and trends of this cation class. The samples with imide-type anions form liquids at ambient temperature, and show good transport properties, comparable to imidazolium or ammonium ionic liquids. Despite the dynamics being significantly accelerated, ether functionalization of the cation favors the formation of crystalline solids. Single crystal structure analysis, ab initio calculations and variable temperature nuclear magnetic resonance measurements (VT-NMR) revealed that cation conformations for the ether- and alkyl-chain-substituted are different in both the solid and liquid states. While ether containing cations adopt compact, curled structures, those with pentyl side chains are linear. The Eyring plot revealed that the curled conformation is accompanied by a higher activation energy for rotation around the carbon-nitrogen bonds, due to the coordination of the ether chain as observed by VT-NMR

Dynamics, cation conformation and rotamers in guanidinium ionic liquids with ether groups

Ionic liquids are modern materials with a broad range of applications, including electrochemical devices, the exploitation of sustainable resources and chemical processing. Expanding the chemical space to include novel ion classes allows for the elucidation of novel structure-property relationships and fine tuning for specific applications. We prepared a set of ionic liquids based on the sparsely investigated pentamethyl guanidinium cation with a 2-ethoxy-ethyl side chain in combination with a series of frequently used anions. The resulting properties are compared to a cation with a pentyl side chain lacking ether functionalization. We measured the thermal transitions and transport properties to estimate the performance and trends of this cation class. The samples with imide-type anions form liquids at ambient temperature, and show good transport properties, comparable to imidazolium or ammonium ionic liquids. Despite the dynamics being significantly accelerated, ether functionalization of the cation favors the formation of crystalline solids. Single crystal structure analysis, ab initio calculations and variable temperature nuclear magnetic resonance measurements (VT-NMR) revealed that cation conformations for the ether- and alkyl-chain-substituted are different in both the solid and liquid states. While ether containing cations adopt compact, curled structures, those with pentyl side chains are linear. The Eyring plot revealed that the curled conformation is accompanied by a higher activation energy for rotation around the carbon-nitrogen bonds, due to the coordination of the ether chain as observed by VT-NMR