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The aim of this work is to provide a better understanding of the interface between graphite and different molecular and ionic liquids. Experimental measurements of the liquid surface tension and of the graphite-liquid contact angle for sixteen ionic liquids and three molecular liquids are reported. These experimental values allowed the calculation of the solid/liquid interfacial energy that varies, for the ionic liquids studied, between 14.5 mN m−1 for 1-ethyl-3-methylimidazolium dicyanamide and 37.8 mN m−1 for 3-dodecyl-1-(naphthalen-1-yl)-1H-imidazol-3-ium tetrafluoroborate. Imidazolium-based ionic liquids with large alkyl side-chains or functionalized with benzyl groups seem to interact more favourably with freshly peeled graphite surfaces. Even if the interfacial energy seems a good descriptor to assess the affinity of a liquid for a carbon-based solid material, we conclude that both the surface tension of the liquid and the contact angle between the liquid and the solid can be significant. Molecular dynamics simulations were used to investigate the ordering of the ions near the graphite surface. We conclude that the presence of large alkyl side-chains in the cations increases the ordering of ions at the graphite surface. Benzyl functional groups in the cations lead to a large affinity towards the graphite surface. [ABSTRACT FROM AUTHOR]

Porous ionic liquids prepared from phosphonium‐based ionic liquids and metal‐organic frameworks (MOFs) are fluid in large ranges of temperature including ambient. It is shown that the ion pairs are too voluminous to enter the pores of the MOF, so the porous liquids remain several months as suspensions with permanent free volume, capable of absorbing large quantities of gases. The increase in gas absorption, when compared with the pure ionic liquids, is proportional to the amount of porous solid in suspension. Structural features of the MOFs and of the ionic liquids are maintained in the suspensions. Thermodynamic analysis and molecular simulations show that the driving force for gas absorption by the porous ionic liquids is energetic as well as structural being controlled by gas‐solid affinity or by the porous liquid free volume. The enthalpy of gas absorption allows easy regeneration of the porous liquid in all cases. The dissolved gases fluidify the porous ionic liquids, different gases having distinct effects on mass transport. The molecular mechanisms that explain the stability of the suspensions and their capacity for gas absorption are identified and point toward easy design rules that will enable numerous applications of these innovative materials as reaction or separation media. [ABSTRACT FROM AUTHOR]

Abstract: Porous liquids can be prepared from the dispersion metal–organic frameworks (MOFs) in ionic liquids (ILs). Porous liquids prepared from 5 % of ZIF‐8 in a phosphonium‐based ionic liquid are capable of absorbing reversibly up to 150 % more nitrogen and 100 % more methane than the pure ionic liquid. [ABSTRACT FROM AUTHOR]

The properties of mixtures of butyltrimethylammonium bis(trifluoromethylsulfonyl)imide, [N4111][NTf2], with poly(ethyleneglycol) dimethyl ether, PEO, were described as a function of PEO chain size by molecular dynamics simulations. Both PEO chain size and mixture composition revealed to play a significant role in determining the structure and the dynamics of the fluids. The remarkably higher viscosity observed for mixtures composed by 0.25 mole fraction of PEO was attributed to the increase in the gauche population of OCCO dihedral of the polyether of longer chains. The negative solvation enthalpy (ΔsolH < 0) and entropy (ΔsolS < 0) revealed a favorable CO2 absorption by the neat and mixture systems. The CO2 absorption was higher in neat PEO, particularly considering longer chains. The gas solubility in the mixtures presented intermediate values in comparison to the neat PEO and neat ionic liquid. The CO2 solutions had their structures discussed in the light of the calculated radial and spatial distribution functions. [ABSTRACT FROM AUTHOR]

Abstract: The concept that ionic liquids are nano-segregated fluids has allowed the rationalization at a molecular level of many of their complex and unusual properties, either as pure substances or as solvents. In this work we will use molecular dynamics simulation results to discuss in a semi-quantitative manner different aspects of such segregation: how it varies within a homologous ionic liquid family; the influence of the nature of the ions in the morphology of the segregated domains; and the interactions of those domains with molecular solutes or solvents. [Copyright &y& Elsevier]

The solubility of xenon in n-hexane and n-perfluorohexane has been studied using both molecular simulation and a version of the SAFT approach (SAFT-VR). The calculations were performed close to the saturation line of each solvent, between 200K and 450K, which exceeds the smaller temperature range where experimental data are available in the literature. Molecular dynamics simulations, associated with Widom's test particle insertion method, were used to calculate the residual chemical potential of xenon in n-hexane and nperfluorohexane and the corresponding Henry's law coefficients. The simulation results overestimate the solubility of xenon in both solvents when simple geometric combining rules are used, but are in good agreement if a binary interaction parameter is included. With the SAFTVR approach we are able to reproduce the experimental solubility for xenon in n-hexane, using simple Lorentz–Berthelot rules to describe the unlike interaction. In the case of nperfluorohexane as a solvent, a binary interaction parameter was introduced, taken from previous work on (Xe + C[sub 2]F[sub 6]) mixtures. Overall, good agreement is obtained between the simulation, theoretical and experimental data. [ABSTRACT FROM AUTHOR]

Highlights: [•] We compare different equation of states, EoS, for an ionic liquid under high pressure. [•] Molecular dynamics, MD, simulations have been used to evaluate the best EoS. [•] MD simulations show that a group contribution model can be extrapolated to P ∼1.0GPa. [•] A perturbed hard-sphere EoS also fits the densities calculated by MD simulations. [ABSTRACT FROM AUTHOR]

In this article, the fifth of a series that describes the parametrization of a force field for the molecular simulation of ionic liquids within the framework of statistical mechanics, we have modeled cations belonging to the hydroxyethylimidazolium, dimethoxy-2-methylimidazolium, and fluoroalkylimidazolium families and anions of the bis(fluorosulfonyl)amide, perfluoroalkanesulfonylamide, and fluoroalkylfluorophosphate families. The development of the force field, created in the spirit of the OPLS-AA model in a stepwise manner and oriented toward the calculation of equilibrium thermodynamic and structural properties in the liquid and crystalline phases, is discussed in detail. Because of the transferability of the present force field, the ions studied here can be combined with those reported in our four previous publications to create a large variety of ionic liquids that can be studied by molecular simulation. The present extension of the force field was validated by comparison of simulation results with experimental crystal structure and liquid density data. [ABSTRACT FROM AUTHOR]

The solvation and the onset of dissolutionof a cellulose Iβmicrocrystal in ionic liquid mediaare studied by molecularsimulation. Ionic liquids can dissolve large amounts of cellulose,which can later be regenerated from solution, but their high viscosityis an inconvenience. Hydrogen bonding between the anion of the ionicliquid and cellulose is the main aspect determining dissolution. Herewe try to elucidate the role of a molecular cosolvent, dimethyl sulfoxide(DMSO), which is an aprotic polar compound, in the system composedof cellulose and the ionic liquid 1-butyl-3-methylimidazolium acetate.We calculated quantities related to specific interactions (mainlyhydrogen bonds), conformations, and the structure of local solvationenvironments, both for a solvated oligomer chain of cellulose andfor a model microfibril composed of 36 chains in the Iβcrystal structure. We compare two solvent systems: the pure ionicliquid and a mixed solvent with an equimolar composition in ionicliquid and DMSO. All entities are represented by detailed all-atom,fully flexible force fields. The main conclusions are that DMSO behavesas an “innocent” cosolvent, lowering the viscosity andaccelerating mass transport in the system, but without interactingspecifically with cellulose or disrupting the interactions betweencellulose with the anions of the ionic liquid. An understanding ofsolvation in mixed solvents composed of ionic liquids and molecularcompounds can enable the design of high-performance media for theuse of biomass materials. [ABSTRACT FROM AUTHOR]