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Type of Document Dissertation Author Shah, Jindal Kiritkumar URN etd-12092004-161900 Title Monte Carlo Simulations of the Ionic Liquid 1-butyl-3-methylimidazolium hexafluorophosphate Degree Doctor of Philosophy Department Chemical Engineering Advisory Committee
Advisor Name Title Prof. Edward J. Maginn Committee Member Keywords
- expanded ensemble
- test particle insertion
- Henry's constant
- free energy
- molecular simulation
- forcefield
- Monte Carlo
- ionic liquid
Date of Defense 2004-08-12 Availability restricted Abstract We report the first molecular simulation study of1-n-butyl-3-methylimidazolium hexafluorophosphate, a widely studied
ionic liquid. Monte Carlo simulations are carried out in the
isothermal-isobaric ensemble to calculate the molar volume, cohesive
energy density and liquid structure as a function of temperature and
pressure. A united atom forcefield is developed using a combination of ab initio calculations and literature parameter values. This forcefield treats the anion hexafluorophosphate as a spherically symmetric interaction site and is later modified to account for the atomistic details of the anion. The results obtained from different forcefields are compared against each other to determine the influence of the molecular representation of the anion on the thermophysical
properties of the ionic liquid. The accuracy of the forcefields in predicting the volumetric properties is assessed by a direct comparison
of the results with experimental observations. Calculated molar volumes (or densities) are within 5 % of experimental values, and a reasonable
agreement is obtained between computed and experimental values of the isothermal compressibility and volume expansivity. Local structure, presented in the form of radial distribution functions, shows that the
anions are found to preferentially cluster in two favorable regions near the cation. We also assess the applicability of the molecular simulations to calculate the Henry's constant of gases with a wide range of solubilities. The results of the Widom test particle insertion method and expanded ensemble simulations are reported. A comparison between the simulation results and experiments shows good agreement. The study reveals inherent difficulty associated with the Widom test particle
insertion method in determining the excess chemical potential, while the expanded ensemble method appears to be somewhat better. Local
organization of solvent molecules about the solute molecules is used to identify interactions governing the observed solubility behavior.
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