Predicting physical properties of ionic liquids

A simple method to predict the densities of a range of ionic liquids from their surface tensions, and vice versa, using a surface-tension-weighted molar volume, the parachor, is reported. The parachors of ionic liquids containing 1-alkyl-3-methylimidazolium cations were determined experimentally, but were also calculated directly from their structural compositions using existing parachor contribution data for neutral compounds. The calculated and experimentally determined parachors were remarkably similar, and the latter data were subsequently employed to predict the densities and surface tensions of the investigated ionic liquids. Using a similar approach, the molar refractions of ionic liquids were determined experimentally, as well as calculated using existing molar refraction contribution data for uncharged compounds. The calculated molar refraction data were employed to predict the refractive indices of the ionic liquids from their surface tensions. The errors involved in the refractive index predictions were much higher than the analogous predictions employing the parachor, but nevertheless demonstrated the potential for developing parachor and molar refraction contribution data for ions as tools to predict ionic liquid physical properties.

Proof of polar ejection from the close-binary core of the planetary nebula Abell 63

We present the first detailed kinematical analysis of the planetary nebula Abell 63, which is known to contain the eclipsing close-binary nucleus UU Sge. Abell 63 provides an important test case in investigating the role of close-binary central stars on the evolution of planetary nebulae. Longslit observations were obtained using the Manchester echelle spectrometer combined with the 2.1-m San Pedro Martir Telescope. The spectra reveal that the central bright rim of Abell 63 has a tube-like structure. A deep image shows collimated lobes extending from the nebula, which are shown to be high-velocity outflows. The kinematic ages of the nebular rim and the extended lobes are calculated to be 8400 +/- 500 and 12900 +/- 2800 yr, respectively, which suggests that the lobes were formed at an earlier stage than the nebular rim. This is consistent with expectations that disc-generated jets form immediately after the common envelope phase. A morphological-kinematical model of the central nebula is presented and the best-fitting model is found to have the same inclination as the orbital plane of the central binary system; this is the first proof that a close-binary system directly affects the shaping of its nebula. A Hubble-type flow is well-established in the morphological-kinematical modelling of the observed line profiles and imagery. Two possible formation models for the elongated lobes of Abell 63 are considered, (i) a low-density, pressure-driven jet excavates a cavity in the remnant asymptotic giant branch (AGB) envelope; (ii) high-density bullets form the lobes in a single ballistic ejection event.

Molecular dynamics simulation of ionic liquids: The effect of electronic polarizability

An electronically polarizable model has been developed for the ionic liquid 1-ethyl-3-methylimidazolium nitrate (EMIM+/NO3-), Molecular dynamics simulation studies were then performed on both the polarizable and nonpolarizable versions of the model. Comparisons of shear viscosity and diffusion constants at 400 K show that the effects of polarizability are quite substantial and the polarizable model results are in better agreement with the experimental values.

The role of Mittag-Leffler functions in anomalous relaxation

The inertia-corrected Debye model of rotational Brownian motion of polar molecules was generalized by Coffey et al. [Phys. Rev. E, 65, 32 102 (2002)] to describe fractional dynamics and anomalous rotational diffusion. The linear- response theory of the normalized complex susceptibility was given in terms of a Laplace transform and as a function of frequency. The angular-velocity correlation function was parametrized via fractal Mittag-Leffler functions. Here we apply the latter method and complex-contour integral- representation methods to determine the original time-dependent amplitude as an inverse Laplace transform using both analytical and numerical approaches, as appropriate. (C) 2004 Elsevier B.V. All rights reserved.

Simplified theory of wideband spectra of liquid H2O and D2O (from 0 to 1000 cm(-1)) due to reorienting polar and vibrating H-bonded water molecules

A semi-phenomenological molecular model is presented, which is capable of describing with the use of analytical formulae, the wideband dielectric(1) and far-infrared spectra of ordinary and heavy water. In the model the vector of a dipole moment is presented as a sum of two components. The absolute value of the first one is constant; the second one changes harmonically with time. The key aspect of this work is consideration of FIR spectra due to the second component. In the context of the modified hybrid model presented in the work, reorientation of the dipoles in the rectangular potential well is considered, as a result of which the librational (near 700 cm (-1)) and translational (near 200 cm (-1)) absorption bands and the microwave Debye relaxation spectrum arise. It is shown that the time-dependent part of a dipole moment contributes most to the translational band, the relevant mechanism is taken to be stretching vibration of the H-bonded molecules. Previous linear-response molecular models were unsuccessful in describing this band (in heavy water) in terms of the complex dielectric permittivity. The spatial and time scales characteristic of water are estimated. (C) 2002 Elsevier Science B.V. All rights reserved.

On the structure and dynamics of ionic liquids

The structure and dynamics of the ionic liquid 1-ethyl-3-methylimidazolium nitrate is studied by molecular dynamics simulations. We find long-range spatial correlations between the ions and a three-dimensional local structure that reflects the asymmetry of the cations. The main contribution to the configurational energy comes from the electrostatic interactions which leads to charge-ordering effects. Radial screening and threedimensional distribution of charge are also analyzed. The motion of a single ion is studied via velocity and reorientational correlation functions. It is found that ions "rattle" in a long-lived cage, while the orientational structure relaxes on a time scale longer than 200 ps. As in a supercooled liquid, the mean square displacements reveal a subdiffusive dynamics. In addition, the presence of dynamic heterogeneities can be detected by analyzing the non-Gaussian behavior of the van Hove correlation function and the spatial arrangement of the most mobile ions. The short-time collective dynamics is also studied through the electric current time correlation function.

Solvation Structure and Transport of Acidic Protons in Ionic Liquids: A First-principles Simulation Study

Ab initio simulations of a single molecule of HCl in liquid dimethyl imidazolium chloride [dmim][Cl] show that the acidic proton exists as a symmetric, linear ClHCl- species. Details of the solvation structure around this molecule are given. The proton-transfer process was investigated by applying a force along the antisymmetric stretch coordinate until the molecule broke. Changes in the free energy and local solvation structure during this process were investigated. In the reaction mechanism identified, a free chloride approaches the proton from the side. As the original ClHCl- distorts and the incoming chloride forms a new bond to the proton, one of the original chlorine atoms is expelled and a new linear molecule is formed.

Simulation of the surface structure of butylmethylimidazolium ionic liquids

Molecular dynamics simulations of the liquid/vacuum surfaces of the room temperature ionic liquids [bmim][PF6], [bmim][BF4] and [bmim][Cl] have been carried out at various temperatures. The surfaces are structured with a top monolayer containing oriented cations and anions. The butyl side chains tend to face the vacuum and the methyl side chains the liquid. However, as the butyl chains are not densely packed, both anions and rings are visible from the vacuum phase. The effects of temperature and the anion on the degree of cation orientation is small, but the potential drop from the vacuum to the interior of the liquid is greater for liquids with smaller anions. We compare the simulation results with a range of experimental observations and suggest that neutron reflection from samples with protiated butyl groups would be a sensitive probe of the structure.

Simulation of interfaces between room temperature ionic liquids and other liquids

The structure and properties of the interfaces between the room temperature ionic liquid dimethylimidazolium chloride ([dmim]Cl) and different Lennard-Jones fluids and between ionic liquid and water have been studied by molecular dynamics simulations, and compared to the ionic liquid-vapour interface. Two contrasting types of interface were investigated, thermodynamically stable interfaces between ionic liquid and vapour and between ionic liquid and Lennard-Jones fluids, and diffusing interfaces between miscible phases of different compositions involving water. The density profiles of different species through the interface are presented. The cations and water molecules near the former type of interface are aligned relative to the surface, but no orientational preference was found near or in the broad diffusing interface. The ionic liquid has a negative electrostatic potential relative to vapour or Lennard-Jones fluid, but is more positive than pure water. This contrast is explained in terms of the relative importance of orientation and concentration differences in the two types of interface.

Conventional free radical polymerization in room temperature ionic liquids: a green approach to commodity polymers with practical advantages

Free-radical polymerization of methyl methacrylate and styrene using conventional organic initiators in the room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([ C(4)mim][PF6]) is rapid and produces polymers with molecular weights up to 10x higher than from benzene; both polymerization and isolation of products were achieved without using VOCs, offering economic as well as environmental advantages.