Research Luncheon Series

---

The Department of Chemical & Biomolecular Engineering invites you to attend the next meeting of the Research Luncheon Series: A Student's Guide to Chemical & Biomolecular Engineering Research Topics

Dr. Selim Elhadj

Staff Scientist, Lawrence Livermore National Laboratory

"Damage mitigation of crystals and glassy materials: practical and fundamental approaches to understanding surface reshaping"

Tuesday, April 21, 2009
12-1:30 p.m.
Othmer Hall, Room 205
Open to the public

Abstract

The first part of this talk will focus on the role of biomolecules in catalyzing growth of calcite, a model crystal system. While the literature has focused on growth modifier in solution as growth inhibitors, sub-micromolar concentrations of peptides were recently shown to actually enhance growth. Our analysis of the chemistry of these peptides allowed, for the first time, extrapolation of the catalytic behavior of full proteins from data involving simple peptides. Water is shown to play an interesting role in modulating this growth during catalysis.

The second part of this talk will focus on nanometer-scale surface reshaping techniques, which can be used for the mitigation of optical damage in high-fluence laser systems. This novel probe-based method guides the reshaping of potassium dihydrogen phosphate (KDP) crystal by exploiting the unique physical chemistry that occurs in the region surrounding a nanoscale tip-surface contact. We present in-situ AFM measurements of the kinetics of this surface remodeling process occurring in solvent containing atmosphere.

Our research found that control of the relative humidity above the surface is essential, and systematically increases the rate of remodeling by orders of magnitude over un-treated surfaces. Using the Gibbs-Thompson relation, which describes surface energy minimization, we present an isotropic analysis of the damaged sites to derive quantitative expressions in good agreement with prediction from independent measurements. Furthermore, this mitigation method can in principle be applied to other soluble materials for repair of damaged or defective surfaces with nanometer scale resolution. Again water, and possibly water structuring, is shown to play an interesting role in modulating reshaping kinetics and thermodynamics.

Time permitting, the third part of this talk will focus on thermography of laser heated silica surfaces. Prediction of the behavior of heated materials, such as evolution of stress and morphology, require knowledge of the temperature profile and history during thermal treatment. Thus, in situ thermographic temperature measurements of fused silica surfaces locally heated with 4.6 and 10.6 mm laser radiation were obtained with mm-spatial and ms temporal resolution, spanning a range of temperatures from 300K up to ca. 3000K. Laser induced stress, evaporation, and surface displacement data are also presented to illustrate the impact of the temperature driving force.

Linear thermal diffusion models were then used to derive an effective thermal conductivity that can then be used to predict the spatial and temporal temperature evolution in the bulk and on the surface of fused silica for any arbitrary exposure. Thermal conductivity estimates show reasonable agreement with classical calculations based on phonon transport, with heat loss contributions due to evaporation at the highest temperatures. These results, in defining the proper computational model and diagnostics, are important to improve control, and thus performance, in applications requiring local heating of silica-based glasses such as laser polishing, optical damage repair, and micro-optical fabrication.

Biography

Elhadj's current research focuses on study of laser-induced heating, melting and evaporation to remove damaged material, heal subsurface cracks, smooth the surface, and anneal residual stress in the affected region of an optic.  Most of the experimental work involves thermal radiation measurements and diagnostics of laser heated optical materials to derive spatial and temporal temperature profiles.  The temperature measurements are then used to validate thermal diffusion models and thus develop a predictive, physics-based computational capability to accurately simulate energy deposition/transport and material hydrodynamics in fused silica under conditions relevant to stress annealing and optical damage mitigation with infrared lasers.

Additionally, he studies the dynamic surface processes of spores and bacteria membrane under different types of environmental perturbations.  Atomic force microscopy is used to achieve sub-nanometer resolution of surface morphology, overgrowth, and membrane components assembly in-situ (liquid).  Using similar techniques for imaging and sample preparation, he studies crystal growth by organic growth-modifiers to provide insights into the fundamental role of water entropy in regulating growth kinetics.  Results of AFM studies in solvent containing atmosphere were used to develop new, probe-based, mitigation approach of non-linear optics damage.

Elhadj received his B.S. 1996, and Ph.D., M.E. in 2001 from Virginia Polytechnic Institute State University. He is currently a staff scientist with interests in condensed matter and materials in Livermore, California.

About the Research luncheon series (RLS)

---

Throughout the Research Luncheon Series, faculty of the Department of Chemical & Biomolecular Engineering and invited guest speakers from both academia and industry, present their research topics for the benefit of current and prospective graduate students, alumni, and chemical engineering professionals. During each luncheon, speakers give a 30-40 minute presentation, immediately followed by a question and answer period. The Department provides free pizza and soda from Valentino's. Typically there is no need to RSVP, however, pizza and pop are first-come, first-served. Interested students of any major, faculty, alumni, and members of AIChE are all encouraged to attend.

Research areas to be presented throughout this series include:

• Biocatalysis
• Biomaterials
• Biomedical Engineering
• Biomolecular Engineering
• Biotechnology
• Energy
• Environmental Engineering
• Heat Transfer
• Materials
• Modeling, Simulation & Theory
• Molecular Medicine
• Nanotechnology
• Polymers
• Reactors, Kinetics & Catalysis
• Separations
• Surface & Interface Science
• Thermodynamics
• Tissue Engineering
• Transport Phenomena, Fluid Mechanics & Fluid Dynamics