2005-06 Departmental Distinguished Seminar Series

H. Henry Lamb, Ph.D.

Department of Chemical and Biomolecular Engineering, North Carolina State University
October 14, 2005
Nanoscience of Catalysis: Probing the Chemistry and Physics of Supported Pt Using InSitu X-ray Absorption Spectroscopy

Professor Lamb's seminar focused on supported Pt catalysis. He explained that supported Pt catalysis was ubiquitous in chemical technology, viz, petroleum refining, fine chemical synthesis and air pollution abatement. Fundamental understanding of the catalysis properties of suported Pt requires knowledge of the chemistry and physics of Pt nanoparticles (clusters) that are only 1-2 nm in size. Moreover, since catalysis is a dynamic pheonmenon, it is necessary to probe the catalysis in situ under high-temperature, high-pressure reaction condistions. X-ray absorption spectroscopy can be applied in situ to elucidate the average size, electronic structure, and chemisorptive properties of supported Pt clusters. This seminar will focus on the geometric and electronic structures of Pt supported on various metal oxide supports, the interaction of supported Pt clusters with chemisorbed hydrogen, and the behavior of supported Pt clusters under NO and NO + O2 atmosphers as it relates to Nox storage-reduction catalysis. Professor Lamb's visited was hosted by Jerry Spivey.

Nicholas Hernjak, Ph.D.

Center for Cell Analysis and Modeling, University of Connecticut Health Center
October 20, 2005
Modeling and Analysis of Intracellular Calcium Signaling Events in Cerebellar Purkinje Cell Spines

Hernjak discussed how long-term depression (LTD) of cerebellar Purkinje cell spines is an important form of synaptic plasicity (a common cellular basis for learning) that is involved in motor learning tasks such as the vestibular-ocular reflex, eye-blink conditioning, and motor coordination. LTD is a lasting decrease in the activity of the synapses between spines on the Purkinje cell dendrites and axons of neighboring granular cells. It has been shown that induction of LTD requires coincident activation of both the parallel fiber (PF) and climbing fiber (CF) inputs of a Purkinje cell. Interestingly, coincident activation of these inputs results in an increase in dendritic spine cytosolic calcium concentration that is significatnly more than the sum of the calcium responses obtained by exciting the PF and CF separately. It is hypothesized that this supralinear calcium response is the mechanism by which the cell detects the coincident activation of teh PF and CF and is the first step in teh mechanism leading to LTD. In this work, dynamic models of a Purkinje spoine are used to identify the precise mechanisms that lead to the onset of the supralinear calcium spke and to investigate the significannc of certain unique characteristics of teh Purkinje cell to this process. The modleing is performed using the Virtual Cell biological modeling framework (http://vcell.org) and includes explicit considertaion of hte roles of a number of calcium buffering species, species diffusion rates, and geometical factors. The modle reproduces the experimentally observed supralinear calcium responses and demonstrates that certain unique biochemical dn geomtrical characteristics of the Purkinje cell's calcium signaling network play necessary roles in generating and localizing the calcium spike. Nonlinear systems analysis is also used to place the biologically-relevant results in the context of known nonlinear phenomena. Hernjak's visit was hosted by Kerry Dooley.

Ahmet Palazoglu, Ph.D.

Department of Chemical Engineering and Materials Science, University of California-Davis October 28, 2005
From Reactors to Proteins: A Journey in Control

Palazoglu explained how an exothermic chemical reaction taking place in a fixed-bed reactor often leads to complex temperature and concentration profiles across the catalyst bed. As product quality and catalyst performance depend critically on how these variables evolve temporally and spatially, it becomes necessary to find ways to influence such profiles through external simulation, such as imposing a cooling regime around the bed. This constitutes the premise for the formulation of an optimal control problem. The determination of such an optimal control(cooling) policy is facilitated by a dynamic model of the process and we use a mathematical invariance condition to calculate it. The simulation of protein folding dynamics can be viewed from a similar vantage point. As the protein molecule folds into its native configuration to perform its function, it goes through a series of critical steps, forming a number of secondary structures via short and long term interactions among its residues. Dynamic simulations provide key information about this folding process and can be crucial in our understanding of diseases such as Alzheimers. The optimal control concepts can be utilized in simulating the motion of proteins and we will demonstrate the use of a course-grained model in following the folding of the Villen headpiece. Palazoglu's visit was hosted by Jose Romagnoli.

Jeff Kelber

Department of Chemistry, University of North Texas
November 11, 2005
Cooperative Surface Reactions at Ordered Alumina Surfaces: What Ultra-High Vacuum Does Not Tell Us about the Real World

Kelber discussed how the interactions of alumina surfaces with H2O and other gas phase species are of broad importance for a multitude of technological applications. He explained that over the last three decades, surface science has made rapid progress in understanding individual molecule-surface interactions under ultra-high vacuum (UHV;P<10-8 Torr). Results [1-3] in his laboratory, however, demonstrates that H2O undergoes previously unsuspected cooperative reactions at the surfaces of ordered alumina thin films at 300K. These reactions occur at PH2O~10-5-10-1 Torr; a pressure range of direct relevance to catalysis, microelectronics processing, and MEMS manufacturing. Under these conditions, the average coverage of H2O <<1, so cooperative reactions involving two or more H2O molecules are not expected. The reactions are apparently initiated at surface defect sites, and result in the loss of all long-range order without the irreversible formation of a surface hydroxide phase, as occurs for PH2O >> 1 Torr. The sensitivity of the thin film to H2O exposures depends on oxide/metal interfacial interactions, with Al2O3/Ni3Al(110) films (incommensurate interface) losing all long range order at H2O exposures where Al2O3/Ni3Al(111) film (commensurate interface) exhibits little effect. Kelber went on to state that other data [4] strongly suggest that such interactions result in the formation of iterstitial atomic hydrogen in the transitional phase films. Recent studies indicate that, in addition to H2O, NH3 and CH3OH show such effects, whereas O2 does not, suggesting the importance of hydrogen bonding to such interactions. The data indicate that alumina and possibly other oxide surfaces are extremely dynamic when in contact with certain adsorbates at intermediate pressures (roughly, 10-7 Torr -1 Torr) and that this technologically relevant pressure range constitutes a reaction environment distinct from either UHV or ambient conditions, dominated by defect chemistry. Kelber discussed the results in light of a model that explained how defect sites might catalyze cooperative, hydrogen bonding processes that envelope the entire surface. Kelber's visit was hosted by Gregory Griffin.

John C. Flake, Ph.D.

Motorola Semiconductor Product Division (Freescale)
November 17, 2005
Nanoscale Device Processing & Soft Fabrication Techniques

Building devices at the nanoscale is challenging because of fundamental physical or material limits and the practical limits of "top-down" fabrication methods. My research focuses on developing new materials and processes to fabricate nanodevices and soft or "bottom-up" techniques that enable self-fabrication.

Nanoscale devices face several low dimensional and quantum effects that were not apparent at the micron scale. Consider the increased effective resistance of CMOS Cu interconnects that arises from electron scattering at interfaces and grain boundaries. One research focus is to explore the limits of copper interconnect fabrication and performance. Fabrication limits are explored via direct copper electrodeposition on barriers with optimization of superconformal electrodeposition processes. Further, optimization of interconnect microstructures and interfaces is needed to mitigate electron scattering and electromigration.

New soft-fabrication techniques also have tremendous promise to overcome traditional top-down fabrication limits (such as sub 100mm optical lithography). Soft techniques take advantage of molecular behavior at surfaces to selectively mask or passivate surfaces, tether nanostructures, or act as catalyst. Examples of soft techniques include: imprint or contact printing, tethering of silicon nanowires, chemical and electrochemical grafting, self-forming silicides and self-doping junctions. These low temperature and low cost processes are particularly attractive for plastic electronics, photovoltaic's, and displays. My research in this area focuses on the fabrication of silicon thin film transistors (TFTs) using low-cost , soft techniques such as electroless metallization and contact printing of self-assembled monolayers on metals. The ultimate vision for soft processes is to replace top-down methods, enabling novel multilevel nanoscale processors, biological & chemical sensors and photovoltaic devices. Flake's visit was hosted by Gregory Griffin.

Yoram Cohen, Ph.D.

Chemical and Biomolecular Engineering Department and Water Technology Research Center, University of California-Los Angeles
December 5, 2005
Membrane Surfaces: Selectivity Enhancement, Fouling Reduction and Mineral Scale Formation

Developments of polymeric and ceramic membranes, primarily over the last two decades, have advanced the use of ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO) and pervaporation applications in water treatment, industrial separation processes, and pollution prevention applications. Chemical and colloidal fouling as well as mineral salt scaling of membranes are major problems that can severely limit membrane effectiveness and lead to increased process costs. In order to develop robust and efficient large-scale membrane separation processes membranes, it is crucial to understand and quantify membrane surface impact on fouling, permeate flux and selectivity.

A promising approach to increasing membrane performance, while mitigating fouling, is the structuring of membrane surfaces at the nano- and molecular levels. Of special interest are tethered polymer-modified (TPM) surfaces that consist of a single molecular layer of terminally-and covalently anchored polymer chains. Such membranes, when based on a stable membrane support, can function even when the tethered polymer phase is swollen by the permeate or feed streams. In order to tailor-design such TPM surfaces, kinetic models of surface graft polymerization were developed to enable the optimization of surface chain density and size with respect to the desired membrane application. The application of TPM surfaces to create selective pervaporation membranes will be presented to demonstrate the role of surface chain spacing and size relative to the membrane pore. Examples of fouling-resistant NF/UF membranes with TPM surfaces will also be discussed for protein filtration and treatment of oil-in-water microemulsions. In these latter applications, grafted chain deformation can affect membrane permeability and solute rejection as illustrated by computational models and permeability studies.

Membrane scaling due to mineral salt crystallization is another fouling problem that limits the performance of p4imarily reverse osmosis (RO) and nanofiltration (NF) membranes. Understanding the impact of surface properties on heterogeneous mineral salt crystallization is paramount to predicting process performance as well as developing effective scale mitigation strategies. Accordingly, our studies have focused on direct measurements of surface crystallization with the goal of quantifying membrane surface scaling propensity, impact of surface chemistry and roughness on surface characterization and identifying membrane module and operating conditions that affect membrane scaling. Finally, the technical and economic feasibility of surface scale mitigation for high product water recovery desalting of brackish water will be discussed. Cohen's visit was hosted by Louis Thibodeaux.

Christopher Kitchens, Ph.D.

School of Chemical and Biomolecular Engineering, Georgia Institute of Technology
February 16, 2006
Gas eXpanded Liquids: Properties and Applications

Gas expanded liquids (GXLs) are a new class of tunable solvents which take advantage of the solvent strength of conventional organic liquids combined with the attractive properties of supercritical fluids. GXLs take advantage of the high solubility of gaseous CO₂ in organic solvents resulting in a highly tunable solvent, at sub-critical pressures. We have implemented various experimental methods, including phase behavior, spectroscopy, and molecular dynamics, to determine detailed properties of GXLs as a versatile solvent media. Further we have applied our finding to a number of applications:

1. A tunable reaction media for homogeneous catalysis that is designed for facile separation of the product and catalyst recycle.

2. Recovery of value added chemicals from forest products biomass.

3. Metallic nanoparticle processing for efficient size-selective fractionation and defect free deposition.

Each of these applications exploits the tunable nature of GXLs, providing significant improvements over conventional processes, in terms of process economics, green chemistry, and scientific potential. Kitchens' visit was hosted by Gregory Griffin.

Byron McCaughey, Ph.D.

Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign
February 23, 2006
Self-healing and self-sensing polymer composites

Lifetime and reliability of current plastics is severely limited by material fatigue and internal cracks. The ability to effectively detect and heal these cracks will greatly improve material performance in commercial and industrial applications ranging from structural plastics to microelectronics. Recently, White et al. has reported the synthesis of self-healing epoxy composites containing monomer microcapsules and embedded catalyst particles. To effectively detect damage as it occurs, expensive and time consuming techniques such as ultrasound, electrical resistance, infra-red thermography, and low energy radiography have been utilized. To improve upon these systems, future research will synthesize a series of polymer composites containing 1) microcapsules filled with healing agents capable of catalyst-free polymerization or 2) a dispersion of chromatic microcrystalline polydiacetylene (PDA) within the composite for crack detection.

The first project will design single component or catalyst free self-healing composites. This composite healing system is based on the encapsulation of highly reactive monomers and curing agents into 50 to 500 ?m polymer capsules. Current routes under consideration for encapsulation are solvent displacement from pre-formed microcapsules, polymer coacervation around healing agent emulsion droplets, physical encapsulation by coaxial jets, and physical or chemical passivation.

The second project will incorporate novel polydiacetylene (PDA) nanoparticles within a structural polymer matrix to provide a simple and cost-effective method of detecting damage. During deformation of a plastic matrix, stress is transferred to incorporated PDA particles that undergo an irreversible transition from blue to fluorescent red. This transition is due to changes in delocalization along the conjugated backbone. McCaughey's visit was hosted by Gregory Griffin.  

Michael Janik, Ph.D.

Department of Chemical Engineering, University of Virginia
March 2, 2006
Density Functional Theory Studies of Acid Catalysis and Electrocatalysis

The ability to link the function of catalytic materials to their atomic level structure guides the rational design of new catalysts. Quantum-chemical methods, such as density functional theory (DFT), can be used to determine atomic structures, reaction energies and activation barriers directly from first-principles, thus enabling the creation of structure-function relationships. The application of DFT methods to the study of heteropolyacid catalysts and the electrocatalysis of methanol oxidation at the anode of a direct methanol fuel cell will be discussed.

Heteropolyacids (HPAs), or polyoxometalates, of the Keggin structure (HnXM12O40) have the ability to act as acid and redox catalysts, and their catalytic properties can be tuned by altering the molecular composition. The correlation between different measurements of acid strength and the barriers to carbenium-ion formation were examined to provide perspective on designing an effective solid acid catalyst for the alkylation of isobutane and butene. The application of DFT methods was extended to modeling the electrocatalytic reaction occurring at the anode of a direct methanol fuel cell. The energetics of CO oxidation were explored employing a DFT-based method of simulating the potential drop across the electrochemical double-layer at the solution/electrode interface. This method allows explicit examination of the effects of solution and an applied potential on reaction energies and activation barriers. Once the key factors which impact anode performance are identified, a simpler model examining only gas-phase reaction energetics over the metal surface is employed for rapid screening of catalyst materials. Initial results of this screening will be discussed. Janik's visit was hosted by Gregory Griffin.

David A. Berry

National Energy Technology Laboratory, U.S. Department of Energy
March 3, 2006
Fuel Processing of Hydrocarbon Fuels For High-Temperature Fuel Cells and the DOE Solid State Energy Conversion Alliance (SECA) Fuel Cell Development Program

Because of their high conversion efficiencies and environmental friendliness, fuel cells are being pursued for a variety of power generation applications. The Department of Energy has embarked on a multi-year program called SECA to develop high temperature solid state fuel cells that could be mass manufactured in core modules for many of these applications. However, these fuel cells operate on hydrogen or hydrogen-rich fuel gas, which must practically be derived from conventional hydrocarbon fuels. This requires the use of reforming technologies such as partial oxidation, auto thermal, or steam reforming. Thermal integration of the fuel processor and fuel cell is a very important consideration and can impact both overall electrical conversion efficiencies and operating characteristics of the system. In addition, technology barrier issues, principally carbon deposition and sulfur poisoning, for catalytic processes involving both the reformer and fuel cell must be overcome to ensure the commercial reality of these technologies. Berry's visit was hosted by Jerry Spivey.

Randy Peterson

Homesite Company, Baton Rouge, Louisiana
March 10, 2006
Giants on the River

Peterson is the author of the well-known book, Giants on the River, which details the history of the Louisiana petrochemical industry. In his seminar, he discussed the history as well as the current issues affecting the local petrochemical industry brought on by the recent hurricanes. Peterson's visit was hosted by Kalliat Valsaraj.

Robert Vacha

Institute of Organic Chemistry and Biochemistry, Prague, Czech Republic
March 21, 2006
Institute of Organic Chemistry and Biochemistry, Prague, Czech Republic

Free energy profiles associated with moving atmospheric gases, radicals and polycyclic aromatic hydrocarbons across the air water interface were calculated as potentials of mean force by classical molecular dynamics simulations. With the employed forcefield the experimental hydration free energies are satisfactory reproduced. The main finding is that both hydrophobic gases (nitrogen, oxygen, and ozone) as well hydrophilic species (hydroxyl radical, hydroperoxy radical, hydrogen peroxide, or PAHs) have free energy minimum at the air/water interface. As a consequence it is inferred that atmospheric gases, with the exception of water vapor, exhibit enhanced concentrations at surface of aqueous aerosols. This has important implications for understanding heterogeneous chemical processes it the troposphere, particularly oxidation of PAHs. Vacha's visit was hosted by Kalliat Valsaraj.

John Fetzer, Ph.D.

Traveling Guest Lecturer of the American Chemical Society
April 7, 2006
The Large Polycyclic Aromatic Hydrocarbons: Chemistry and Analysis

Polycyclic aromatic hydrocarbons (PAH) are an almost ubiquitous class of compounds. The presentation will focus on many of the general aspects of their chemistry, analysis, and occurrence. The focus will shift from an important industrial issue that led into many new discoveries to the organic synthesis, chromatographic and spectral behaviors, occurrences, and chemistry of PAH.

Dr. John C. Fetzer, formerly of Chevron Research in Richmond, California, is a recognized expert in the analysis of PAH and petroleum-related materials. He has served as the president of the International Society on Polycyclic Aromatic Compounds, is the topical editor for analytical chemistry for the journal Polycyclic Aromatic Compounds, and has served or is serving on the editorial advisory boards for the Journal of Chromatography, Analytical Chemistry, and Analytical and Bioanalytical Chemistry. He has published over 140 technical and review articles, holds three US patents on PAH chemistry and analysis, and is the author of The Chemistry and Analysis of the Large (C>=24C) Polycyclic Aromatic Hydrocarbons (Wiley-Interscience, 2000). Fetzer's visit was hosted by Judy Wornat.

Robert Beitle, Ph.D.

Green Chemical Process Design and Development, University of Arkansas
April 21, 2006
Bioseparation in the post genomic/proteomic era

Separating and purifying a desired product from intracellular materials, fermentation broth, or cell culture supernatant is a crucial and challenging component of commercial biochemical engineering since recovery usually comprises a major part of the production cost. With sufficient proteome information available now we are able to modify the host cell to further increase efficiencies during bioseparation not by enhancing target protein properties, but by altering the nature of the contaminating protein pool. This seminar will provide a perspective on our past and ongoing work, and will illustrate the interplay between protein identification, metabolism, mutation, and the use of E. coli mutants with a minimized contaminant pool. Beitle's visit was hosted by James Henry.