Edward Maginn

The research in our group focuses on developing a fundamental understanding of the link between the physical properties of materials and their chemical constitution. Much of our work is devoted to environmentally related applications, both in remediation and environmentally benign chemical processing (i.e. prevention). The main tool we use is molecular simulation. In this approach, a detailed geometric and energetic model of the material of interest is created and then simulated using large scale high performance computing. By subjecting the resulting molecular conformations to statistical mechanical analysis, macroscopic properties may be computed.

Our current focus areas are: ionic liquids, a class of non-volatile liquids that show great promise as replacements for conventional volatile organic solvents; sorption, diffusion and ion exchange in nanomaterials, with a particular emphasis on ion exchange of radioactive cations in titanosilicate and polyoxometalate materials; fluid property calculation, where we are most interested in making quantitative predictions of thermodynamic and transport properties of fluids of industrial interest; and simulation methodologies, where our goal is to develop and apply novel computational methods that enable difficult systems to be examined with molecular simulation.

Publications

Neeraj Rai and Edward J. Maginn. Vapor-Liquid Coexistence and Critical Behavior of Ionic Liquids via Molecular Simulations. Journal of Physical Chemistry Letters, 2:1439-1443, 2011.  Critical properties have played central role in the development of corresponding state theories to provide a unified framework for understanding phase Behaviour of both polar and non–polar fluids 1, 2 . Although our understanding of phase behaviour of non–ionic compounds has matured, the progress in understanding the phase behavior room temperature ionic liquids is hindered due to the complexity of molecular structure and presence of long range Coulombic interactions. The lack of thermal stability of these ionic liquids virtually eliminates direct experimental determination of critical points. Here we report the first in silico vapour–liquid phase diagrams of room temperature ionic liquids employing atomistic force field. We show that the critical temperature decreases with the increase in the alkyl side chain length (nonpolar segment), and that the vapour phase consists mainly of neutral ion–pairs at low temperatures but clusters of up to 20 ion–pairs are observed at higher temperatures. Our work lays down foundation for developing generalized frame work for understanding vapor–liquid phase behaviour of ionic liquids.

Hongjun Liu, Yingxi Zhu and Edward J. Maginn. Molecular Simulation of Polyelectrolyte Conformational Dynamics Under and AC Electric Field. Macromolecules, 43:4805-4813, 2010.  We use a coarse-grained molecular dynamics method to study the behavior of a flexible polyelectrolyte (PE) chain in an explicit salt solution with varied valence under an ac electric field. Simulations in the absence of electric field and under dc electric field are used to determine the critical field strength and intrinsic chain relaxation frequency. Our results show that the PE chain breathes with applied ac frequency and becomes dynamically stretched, only when the applied field strength exceeds the critical field strength and the applied ac frequency is comparable to or less than the intrinsic relaxation frequency of the PE chain.

Gabriele Raabe and Edward J. Maginn. Molecular Modeling of the Vapor-Liquid Equilibrium Properties of the Alternative Refrigerant 2,3,3,3-Tetrafluoro-1-propene (HFO-1234yf). Journal of Physical Chemistry Letters, 1:93-96, 2010.  The European Union legislation 2006/40/EC results in a phase-out of the presently used tetrafluoroethane refrigerant R134a from automotive heating ventilation and air conditioning systems. This necessitates the adoption of alternative refrigerants, and 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf) is currently regarded as the most promising alternative refrigerant. However, the lack of experimental data hampers independent studies on its performance in technical applications. We have developed a force field for HFO-1234yf that enables reliable predictions of its thermophysical properties via molecular simulation. The simulation results complement experimental data and provide a molecular-level perspective of the fluid behavior. In this letter we present the force field and its validation using Gibbs ensemble simulations on its vapor liquid equilibria.

Mara Freire Martins, Catarina Neves, Artur Silva, Luis Santos, Isabel Marrucho, Luis Paulo Rebelo, Jindal Shah, Edward J. Maginn and Joao Coutinho. 1H NMR and Molecular Dynamics evidence for an Unexpected Interaction on the Origin of Salting-in/out Phenomena. Journal of Physical Chemistry B, 114:2004-2014, 2010.