Liquid−Vapor Coexistence in a Primitive Model for a Room-Temperature Ionic Liquid

Martín-Betancourt, Marianela; Romero-Enrique, J. M.; Rull, Luis F.

doi:10.1021/jp903709k

Cited by 17 publications

(22 citation statements)

References 35 publications

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“…Despite a heavy investment of computer time, the condensation transition in DHS fluids has not been observed directly in simulations of systems with sufficient size, and with suitable treatments of the long-range dipolar interactions [6][7][8][9][10]. Many attempts have been made to "sneak up" on a phase transition by simulating models that correspond to pure DHSs in some limit, but the transition always disappears before the limit is reached [11][12][13][14][15][16][17]. It has been shown theoretically, and with several different approaches, that chain formation may preclude fluid-fluid phase separation [18][19][20][21].…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics of ferrofluids in applied magnetic fields

2013

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The thermodynamic properties of ferrofluids in applied magnetic fields are examined using theory and computer simulation. The dipolar hard sphere model is used. The second and third virial coefficients (B 2 and B 3 ) are evaluated as functions of the dipolar coupling constant λ, and the Langevin parameter α. The formula for B 3 for a system in an applied field is different from that in the zero-field case, and a derivation is presented. The formulas are compared to results from Mayer-sampling calculations, and the trends with increasing λ and α are examined. Very good agreement between theory and computation is demonstrated for the realistic values λ 2. The analytical formulas for the virial coefficients are incorporated in to various forms of virial expansion, designed to minimize the effects of truncation. The theoretical results for the equation of state are compared against results from Monte Carlo simulations. In all cases, the so-called logarithmic free energy theory is seen to be superior. In this theory, the virial expansion of the Helmholtz free energy is re-summed in to a logarithmic function. Its success is due to the approximate representation of high-order terms in the virial expansion, while retaining the exact low-concentration behavior. The theory also yields the magnetization, and a comparison with simulation results and a competing modified mean-field theory shows excellent agreement. Finally, the putative field-dependent critical parameters for the condensation transition are obtained and compared against existing simulation results for the Stockmayer fluid. Dipolar hard spheres do not undergo the transition, but the presence of isotropic attractions, as in the Stockmayer fluid, gives rise to condensation even in zero field. A comparison of the relative changes in critical parameters with increasing field strength shows excellent agreement between theory and simulation, showing that the theoretical treatment of the dipolar interactions is robust.

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Section: Introductionmentioning

confidence: 99%

Thermodynamics of ferrofluids in applied magnetic fields

2013

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“…Results from MD simulations strongly suggest the formation of clusters of ILs in the gas phase at room temperature. [46,48,49] However, this does not concern the BFH cycle, because at the elevated temperatures at which vaporization enthalpies are measured, single ion pairs prevail.…”

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confidence: 99%

Going Full Circle: Phase‐Transition Thermodynamics of Ionic Liquids

Preiss

Verevkin

Koslowski

et al. 2011

Chemistry A European J

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We present the full enthalpic phase transition cycle for ionic liquids (ILs) as examples of non-classical salts. The cycle was closed for the lattice, solvation, dissociation, and vaporization enthalpies of 30 different ILs, relying on as much experimental data as was available. High-quality dissociation enthalpies were calculated at the G3 MP2 level. From the cycle, we could establish, for the first time, the lattice and solvation enthalpies of ILs with imidazolium ions. For vaporization, lattice, and dissociation enthalpies, we also developed new prediction methods in the course of our investigations. Here, as only single-ion values need to be calculated and the tedious optimization of an ion pair can be circumvented, the computational time is short. For the vaporization enthalpy, a very simple approach was found, using a surface term and the calculated enthalpic correction to the total gas-phase energy. For the lattice enthalpy, the most important constituent proved to be the calculated conductor-like screening model (COSMO) solvation enthalpy in the ideal electric conductor. A similar model was developed for the dissociation enthalpy. According to our assessment, the typical error of the lattice enthalpy would be 9.4 kJ mol(-1), which is less than half the deviation we get when using the (optimized) Kapustinskii equation or the recent volume-based thermodynamics (VBT) theory. In contrast, the non-optimized VBT formula gives lattice enthalpies 20 to 140 kJ mol(-1) lower than the ones we assessed in the cycle, because of the insufficient description of dispersive interactions. Our findings show that quantum-chemical calculations can greatly improve the VBT approaches, which were parameterized for simple, inorganic salts with ideally point-shaped charges. In conclusion, we suggest the term "augmented VBT", or "aVBT", to describe this kind of theoretical approach.

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“…MC simulations of ionic systems within the grand canonical ensemble potentially encounter numerous sampling difficulties as highlighted in previous works. [27][28][29] The main challenge is to achieve suitable acceptance of insertion and deletion moves in the low density vapor phase. To address this issue, we performed these moves using the distance-biasing scheme of Orkoulas and Panagiotopoulos.…”

Section: Simulation Detailsmentioning

confidence: 99%

Understanding the influence of Coulomb and dispersion interactions on the wetting behavior of ionic liquids

Rane

Errington

2014

The Journal of Chemical Physics

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We study the role of dispersion and electrostatic interactions in the wetting behavior of ionic liquids on non-ionic solid substrates. We consider a simple model of an ionic liquid consisting of spherical ions that interact via Lennard-Jones and Coulomb potentials. Bulk and interfacial properties are computed for five fluids distinguished by the strength of the electrostatic interaction relative to the dispersion interaction. We employ Monte Carlo simulations and an interface-potential-based approach to calculate the liquid-vapor and substrate-fluid interfacial properties. Surface tensions for each fluid are evaluated over a range of temperatures that spans from a reduced temperature of approximately 0.6 to the critical point. Contact angles are calculated at select temperatures over a range of substrate-fluid interaction strengths that spans from the near-drying regime to the wetting regime. We observe that an increase in the relative strength of Coulombic interactions between ions leads to increasing deviation from Guggenheim's corresponding states theory. We show how this deviation is related to lower values of liquid-vapor excess entropies observed for strongly ionic fluids. Our results show that the qualitative nature of wetting behavior is significantly influenced by the competition between dispersion and electrostatic interactions. We discuss the influence of electrostatic interactions on the nature of wetting and drying transitions and corresponding states like behavior observed for contact angles. For all of the fluids studied, we observe a relatively narrow range of substrate-fluid interaction strengths wherein the contact angle is nearly independent of temperature. The influence of the ionic nature of the fluid on the temperature dependence of contact angle is also discussed.

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Liquid−Vapor Coexistence in a Primitive Model for a Room-Temperature Ionic Liquid

Cited by 17 publications

References 35 publications

Thermodynamics of ferrofluids in applied magnetic fields

Thermodynamics of ferrofluids in applied magnetic fields

Going Full Circle: Phase‐Transition Thermodynamics of Ionic Liquids

Understanding the influence of Coulomb and dispersion interactions on the wetting behavior of ionic liquids

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