1,720,980 research outputs found
From molten salts to ionic liquids: effect of ion asymmetry and charge distribution
No full textWe studied the influence of ion shape asymmetry and charge distribution on the liquid structure and transport properties of ionic liquids by the molecular dynamics of schematic models. The ion structure asymmetry results in a less compact packing, while the charge distribution gives potential wells with reduced depth with respect to the single-site centred charges. Both these aspects contribute to accelerate the dynamics of the melt. The liquids display a clearly detectable supercooled region, in which two different liquid structures appear to be present contemporarily. The diffusion process, as usual in supercooled liquids, proceeds through a cage-escaping process; the diffusion constants nevertheless show an opposite behaviour with respect to expectations from the cavity size distribution. The observed transient liquid structure can help to explain some surprising features of the diffusive behaviour of these systems
Ab Initio Study of the Diels-Alder Reaction of Cyclopentadiene with Acrolein in a Ionic Liquid by KS-DFT/3D-RISM-KH Theory
No full textWe study the Diels-Alder reaction between cyclopentadiene and acrolein in a model room-temperature ionic liquid ([mmim][PF(6)]) as a solvent. The calculations have been performed with the KS-DFT/3D-RISM-SCF theory, where the reactants and transition state (TS) have been represented at a OM level, while the solvent is represented by a 3D distribution of classical (charge + LJ) sites obtained by solving the 3D-RISM integral equation. We show that this method, being computationally efficient, is able to reproduce the main experimental features displayed by the experiments, concerning the reaction rate enhancement and augmentation of the endo/exo ratio in ionic liquids (ILs). We find that the IL distorts noticeably the transition state geometry, inverting the order of the frontier orbitals and leading to an enhancement of the asynchronicity of the reaction. Finally, we find, in agreement with recent work, that formation of the hydrogen bond between the unique C2 hydrogen of the imidazolium ring is not essential to explain the peculiar features of these reactions in ILs
Excess entropy scaling of diffusion in room-temperature ionic liquids
No full textExcess entropy scaling relationships for diffusivity of ions in room-temperature ionic liquids are tested using molecular dynamics simulations for a model ionic liquid, dimethyl imidazolium chloride. The thermodynamic excess entropy of the single ions (estimated from the ion-ion pair correlation functions) is shown to be very strongly correlated with the diffusivity. An essential feature of these systems, the fact that the heavier and larger cation has a greater diffusivity with respect to the anion, is correctly captured by the excess entropy calculations, which estimates the diffusivity ratio between the two ions with noticeable precision. (C) 2010 American Institute of Physics. [doi:10.1063/1.3431535
Highly concentrated "solutions" of metal cations in ionic liquids: current status and future challenges
No full textIn this article we summarize a series of conditions that allow highly concentrated "solutions" of metal cations in ionic liquids to be obtained, evidencing structural features and some of the most important physico-chemical properties of these systems. We try to emphasize aspects and problems that are not conventionally discussed in detail in the literature. In particular, we provide a full length discussion on the topics of: (i) solvation of metal salts in ionic liquids, (ii) anion coordinating ability and homologous and heterogeneous complexes. A brief outlook into future perspectives of metal containing ILs is also provided
A RISM approach to the liquid structure and solvation properties of ionic liquids
No full textWe test for the first time the performance of the reference interaction site model (RISM) to predict the liquid structure and solvation of room-temperature ionic liquids (RTILs) represented with different degrees of accuracy. The model gives satisfactory results, proposing itself as a possible method to explore and to describe at a chemically realistic level the solvation shell in ionic liquids, which is believed to play a fundamental role in the static electronic and vibrational properties of these systems
Ionic liquids: Solvation ability and polarity RID E-4986-2010
No full textThe role of ionic liquids (ILs) as solvents in chemistry is limited by the poor understanding of the solvation phenomenon in these media. The usual classification criteria used for molecular solvents through various experimental measurements fail to insert ILs into a univocal classification for ILs. Here, we first discuss the unsuitability of the usual interpretative scheme for molecular liquids and elucidate schematically the mechanism of solvation in ILs, pointing out the peculiarities that differentiate them with respect to molecular liquids. Second, we focus on reactivity and reaction kinetics in ILs, underlining the many problems that the complexity of these media reflects on the interpretation of kinetic data and some possible approaches to understand qualitatively the (often not trivial) kinetic problems for reactions performed in ILs
Solvation thermodynamics of alkali and halide ions in ionic liquids through integral equations
No full textIn this work, we study the solvation thermodynamics and other solvation properties of small ions in two room-temperature ionic liquids, dimethyl imidazolium hexafluorophosphate [mmim] [pf6] and dimethyl imidazolium chloride [mmim][cl] with the reference interaction site model (RISM). The nature of the charge affects several aspects of solvation, from electrostriction to the mutual disposition of cations around the solute; nevertheless, the long-range screening behavior of the liquid appears to be insensitive to both charge and dimensions of the solute. The ion solvation is energy driven, as expected for the nature of the solvent, and displays a marked asymmetry between cation and anion solvation chemical potential. Such asymmetry is dependent, even qualitatively, on the ionic liquid chosen as solvent. Partial molar volumes of ions in solution are found to follow the nature of ion-solvent interaction. (C) 2008 American Institute of Physics
Understanding solvation processes in ionic liquids through RISM-SCF and Supermolecular calculations
No full textMutual information does not detect growing correlations in the propensity of a model molecular liquid
Full text linkThe dynamical spatial correlations detected by the mutual information (MI) in the isoconfigurational particle displacements of a monodisperse molecular viscous liquid are studied via molecular-dynamics simulations by changing considerably both the molecular mobility and the degree of dynamical heterogeneity. Different from atomic liquids, the MI correlation length does not grow on approaching the glass transition by considering the liquid both in full detail as a collection of monomers and as a coarse-grained ensemble of molecular centers of mass. In the detailed picture, it is found that: (i) the MI correlations between monomers are largely due to inter-molecular correlations, (ii) the MI length scale is numerically identical, within the errors, to the correlation length scale of the displacement direction, as drawn by conventional correlation functions. The time evolution of the MI spatial correlations complies with the scaling between the fast vibrational dynamics and the long-time relaxation. Our findings suggest that the characteristics of the MI length scale are markedly system-dependent and not obviously related to dynamical heterogeneity
- …
