James A. O'Brien

Associate Professor of Chemical Engineering

321B Mason Laboratory, (203) 432-4382, james.obrien@yale.edu


Our research applies thermodynamics and statistical mechanics to various problems in materials science and chemical processes. Much of the work is carried out by computer experiments, such as Monte Carlo simulations, either on a local workstation or on the Cray C90 at the Pittsburgh Supercomputing Center.

We also distribute the Windows-based program REACT! A Chemical Equilibrium Calculator, which is useful for teaching thermodynamics and kinetics courses.

Morphology and growth phenomena Many important properties of materials are determined by either surface or constituent particle morphology which, in turn, depend on the conditions under which the material is manufactured. We are studying a class of computer models for cluster growth in an ongoing project aimed at understanding how morphology develops. The primary tool in this work is contour dynamics simulation, a boundary element method by which we track the development of growing simulated interfaces. So far, we have investigated the transition between reaction and diffusion control in such systems, as well as a variant of Ostwald ripening, or coarsening.

Aerosol transport phenomena Most aerosol processes involve the use of particles entrained in high-speed gas flows e.g., impaction separators, which exploit inertial effects to cause a separation. For very small particles, Brownian motion is important, but it cannot be handled easily in terms of diffusion (our usual term for equilibrium Brownian motion), since the system is being deliberately forced out of equilibrium. We are studying transport phenomena involving this type of particle, using nonequilibrium Brownian dynamics simulation. Applications include optimization of the design of impactor flow fields, and the prediction of particle deposition on surfaces (e.g., optimal design of filter elements; environmental and physiological effects of airborne particulate pollutants).

Physical adsorption equilibria The prediction of multicomponent adsorption equilibria on commercially useful adsorbents (e.g., microporous activated carbon) is a generally unsolved problem, even for small gas phase molecules such as methane and carbon dioxide. The major difficulty arises from the chemical and geometric (and hence energetic) heterogeneity of these adsorbents. We are pursuing approaches to this problem using molecular thermodynamics applied to single idealized pore systems (simulation and theory), as well as pore size distribution analysis of the adsorbents. Most recently, we have developed a new method called the multi-space adsorption model (MSAM) for quantitative predictions of multicomponent equilibria. This project is a collaboration with Dr. Nigel Seaton of the Department of Chemical Engineering at the University of Cambridge in the UK. We also have made available a simulation-based technique for activated carbon characterization.

A computer-generated image of MCM-41, diameter 3nm, with adsorbed methane and ethane molecules.


Molecular thermodynamics of supercritical fluids Supercritical fluids offer many important advantages as media for chemical reactions: solute diffusivities are about an order of magnitude higher than in liquids, and solubilities are usually much higher than in gases at comparable temperatures. Further, all of these properties are readily varied by suitable changes in pressure. However, the fundamental physical chemistry of supercritical fluid mixtures is not well understood. Therefore, in a collaborative project with Department of Chemical Engineering at the University of Colorado, we are studying molecular interactions and clustering in supercritical fluids. The goal of the work is an increased understanding of molecular effects in the supercritical state, with a view to exploiting supercritical fluids as reaction media. We have already identified several key effects which have not been adequately considered in the existing literature of the field. Our tools in this work include various types of thermodynamic simulation such Monte Carlo, molecular dynamics and equilibrium Brownian dynamics. These are supplemented with the more traditional statistical mechanical integral equation theories. The simulations and modeling assist the interpretation of the primary experimental data measured in Randolph’s lab using electron paramagnetic resonance (EPR) spectroscopy.

Selected Publications