Molecular thermodynamic modeling of ionic liquids using the perturbation-based linear Yukawa isotherm regularity

• Published in: Journal of physics. Condensed matter 2016-06, Vol.28 (23), p.235101-235101
• Main Authors: Sohrabi Mahboub, Mahdi, Farrokhpour, Hossein
• Format: Article
• Language: English
• Subjects: average effective pair potential (AEPP); Condensed matter; Density; effective pair molecular parameters; equation of state; Ion pairs; Ionic liquids; Isotherms; linear Yukawa isotherm regularity (LYIR); Mathematical models; Modelling; Regularity; thermodynamic modeling
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/28/23/235101

In this paper, we present the results of an extensive study on a novel approach to the molecular modeling of pure ionic liquids (ILs) that incorporates the perturbed thermodynamic linear Yukawa isotherm regularity (LYIR), which is derived based on an effective nearest neighboring pair attractive interaction of the Yukawa potential. The LYIR was used to model the densities of ILs up to high pressures (35 MPa) and in the temperature range 293.15 to 393.15 K. To use the LYIR for ILs, a simple molecular model was proposed to describe their molecular structure, in which they were considered as a liquid consisting of the ion pairs moving together in the fluid, and each ion pair was assumed to be a one-center spherical united atom. The ILs under consideration contained one of the IL cations [C2mim]+, [C4mim]+, [C7mim]+, [C8mim]+, [C3mpy]+, [C3mpip]+, [C3mpyr]+ or [C4mpyr]+, and one of the IL anions [BF4]−, [C(CN)3]−, [CF3SO4]− or [NTf2]−. The reliability and physical significance of the parameters as well as the proposed molecular model were tested by calculating the densities of pure imidazolium-, pyridinium-, piperidinium- and pyrrolidimium-based ILs. The results showed that the LYIR can be used to predict and reproduce the density of ILs in good agreement with the experimental data. In addition, the LYIR enabled us to determine the physical quantities, such as an effective Yukawa screening length, λeff, the product of the effective energy well depth and the effective coordination number, ( eff/k)zeff, the contribution of the non-reference thermal pressure and also the influence of the anionic and cationic structure on the λeff parameter. The standard deviation of the IL densities predicted in this work is lower than those calculated by the one other important equation of state reported in the literature.