PEOPLE · FACULTY

FACULTY

Eldred H. Chimowitz
Professor and Associate Chair
Ph.D. 1982, University of Connecticut

203 Gavett Hall
(585)275-8497
chim@che.rochester.edu

Website

http://www.che.rochester.edu/~chim/

Courses

ChE 150: Green Engineering for a Sustainable Environment
ChE 272: Process Dynamics and Control
ChE 273: Process Design

Scholarly Activities:

Selected Publications
Recent Presentations
Book

Music Activities:

B Flat Blues
Devil Ways
All Blues
Blue & Green
Funk

Interactive Simulation Computer Programs:

Heat Exchanger System
Wind Power EXCEL Spreadsheet Calculator
Confined Fluid Equation of State Model
Fuel Cell Modeling

Research Topics: Critical Phenomena, Statistical Mechanics of Fluids and Computer-Aided Design

Research Overview: Computer Simulations of Thermodynamic Properties of Mesoporous Materials: A fundamental understanding of the properties of fluids confined in porous materials is a problem of continuing importance in chemical/materials engineering. These materials can range from being completely random in structure, to those existing as periodic, ordered materials. Zeolites, for example, are ordered materials with crystalline, open pore structures whose size/shape characteristics make them useful as catalysts and/or catalyst support materials. Another important class of substrates, often referred to as "disordered media", possess quenched, random pore structures; the term quenched refers to the fact that during the formation process the mechanical structure of these materials is fixed in place through a quench processing step. Inorganic membranes, aerogels and other substances derived from sol-gel processes are representative of materials in this class with applications proposed in the areas of ceramic membranes, catalyst supports, gas sensors and nanofiltration devices.

Phase transitions and the nature of the critical behavior of fluids confined in these systems is often an important issue in process applications. We employ molecular simulation methods to study the thermodynamic and transport properties in these systems. In homogeneous bulk fluid systems critical behavior occurs when the dominant length scale in the system, the correlation length, diverges to infinity. In a porous structure, however, the nature and extent of percolation pathways in the porous matrix determine how the correlation length grows beyond the length of the average pore size. In this way, geometric confinement leads to novel critical behavior, often quite different to that observed in the corresponding homogeneous bulk phase. It is these phenomena that are of interest to our research. Our motivation for pursuing this work has arisen from experimental work in the group aimed at studying the use of these materials in various processes. These involve the supercritical processing of porous materials and the development of energy efficient inorganic membrane separation processes to supplant, where possible, organic solvent use in chemical separations.

Diffusion Through Dynamic Network Structures: Static percolation theory often concerns itself with the topological connectivity of a system consisting of a static collection of randomly distributed conducting sites surrounded by vacant or non-conducting sites. Particles called random walkers (walkers or the term carriers are used interchangeably in the literature) can move throughout the system by “hopping” from one conducting site to another, as long as the sites are “connected” which is often defined to be that they are nearest neighbors. This theory predicts a threshold for the concentration of conducting sites, above which a sharp increase in conductivity is observed. Conductivity here is defined as the flux of random walkers through the conducting site network from one end of the system to the other. A wide range of applications have successfully employed variants of this theory, such as ionic conduction in polymeric, amorphous, or glassy ceramic electrolytes, diffusion in biological tissues, conduction in semiconductors, gelation in polymers, turbulent diffusion, forest fire propagation and the efficacy of corrosion-resistant metal-organic coatings.
However, with this theory the motion of the carriers is restricted to the conducting site cluster in which the carrier initially belongs. Thus, below the site percolation threshold, the mean square displacement of a walker in the system will approach a finite value after some time with the concomitant result that the dc conductivity through the network will become zero in the long time limit. In many real systems, however, this will not be the case, since the structure can undergo microscopic rearrangements with time. This “network dynamics” continually affects the pathways through which conduction can occur and can have a dramatic effect on diffusion in the network. We illustrate this in figure 1 where simulation results for the mean square displacement of a walker in a 2d Ising lattice structure are shown for a site density well below the system’s static percolation threshold. One sees that at some point in the static system, transport comes to a halt while in the dynamic system it proceeds apace.|

Figure 1. Diffusive behavior in a random, uncorrelated percolation system. Shown are simulation results for static and dynamic structures below the static percolation threshold .

We are interested in developing theories that, in principle, deal with the behavior of such dynamic systems. A few practical examples of systems that have been analyzed in these terms include: certain bio-membranes, polymer electrolytes, oil continuous micro-emulsions and microemulsion mixtures consisting of thermodynamically stable, self-assembled aggregates of surfactant molecules surrounding small droplets of either oil-in-water or water-in-oil.