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Materials
^ Localized Corrosion of Passive Metals
R. C. Alkire,* E. Webb, M. Knight, T. Pricer, L. Zhu, J. Gray, D. Veyret, M. Georgiadou, F. Topin, T. Suter, C. Paik, J. Ganley
U.S. Department of Energy, DE-FG02-96ER45439

(In cooperation with the Materials Research Laboratory)

The materials investigated in this study are those metals and alloys that tend to form protective surface layers spontaneously and thereby become susceptible to localized corrosion when the protective layers are disturbed. Among these are Al, Ni, Cu, and their alloys, including stainless steels. Special attention is given to integration of the experimental approach with a Web-based modeling approach that accounts for transport, kinetic, and thermodynamic phenomena over a wide range of time and length scales. Topics under study include local breakdown in pits, crevices, and cracks.

^ Use of Very High Pressure to Investigate the Structure of Matter
H. G. Drickamer,* G. Yang, Y. Li
U.S. Department of Energy, DE-FG02-96ER45439

(In cooperation with the Materials Research Laboratory and the Departments of Physics and Chemistry)

The basic thesis of this research is that high pressure is an essential tool for understanding electronic phenomena in condensed systems. With increasing compression there is increased overlap among electronic orbitals. Different types of orbitals are perturbed to different degrees. A study of these perturbations permits one to characterize electronic states and excitations and to test theories. This work is focused on three areas: pressure effects on light-emitting polymers potentially useful as light-emitting diodes; the use of a newly developed device for controlled stretching of polymers to compare the effects of pressure and stretch on optical and related properties; and the emission characteristics of oligomers and three dimensional polymers (dendrimers) in dilute solution in various polymeric media.

^ Adsorption of Polymers on Surfaces with Chemical Heterogeneity on Nanometer Scale
V. K. Gupta,* Y. Huang
University of Illinois; U.S. Department of Energy, DE-FG02-96ER45439

(In cooperation with the Materials Research Laboratory)

Adsorption of polymers is relevant to numerous applications such as colloidal stabilization, adhesion, biochemical processes, and chromatography. Surface heterogeneity is common in these applications, and yet there is virtual nonexistence of systematic, quantitative experimental results on such surfaces. This research is focused on the kinetics of adsorption of polymers at solid surfaces and study of the influence of chemical heterogeneity. Using the tools of molecular assembly, researchers create surfaces that are well-defined and energetically heterogeneous on length-scales commensurate to typical polymer chains (RG~10-100nm). The goal is to understand the interplay between physicochemical properties of the adsorbing polymer chains and characteristics of the surface heterogeneity.

^ Chemical Selectivity of Organized Assemblies of Macrocycles on Solid Substrates
V. K. Gupta,* J. Faull
University of Illinois; National Science Foundation, CTS 9732691, CTS 9875467; American Chemical Society, Petroleum Research Fund

Chemically selective surfaces are essential to chemical and biochemical sensing as well as new processes for chemical purification/separation. This research centers on surfaces that contain immobilized macrocycles as model receptor molecules with a potential for complexing with organic adsobates in solution via guest-host interactions. The proposed research addresses the need for understanding how characteristics such as surface density of receptor molecules, steric barriers to binding, or molecular flexibility of receptor chains can be manipulated to enhance the guest-host binding. Optimization of the guest-host complexation properties will facilitate new analytical/diagnostic procedures and applications where catalytic activity can be confined to an interface through guest-host complexation.

^ Photochromic Self-assembled Surfaces Formed Using Polypeptides
V. K. Gupta,* A. Williams
University of Illinois; National Science Foundation, CTS 9732691, CTS 9875467; American Chemical Society, Petroleum Research Fund

This research explores molecular-level principles for photocontrol of the optical and interfacial properties of self-assembled monolayers. Toward the goal of enhancing the photostimulated response, researchers are exploring the use of photoresponsive polymers such as α-helical polypeptides because these biological macromolecules are structurally anisotropic and possess macrodipoles. By establishing principles based on which structure and organization of surfaces can be engineered for optimal control of physico-chemical properties, the proposed research will permit light-assisted manipulation of adsorption-desorption of biomolecules on surfaces, wetting-dewetting of polar or nonpolar fluids, and optical anisotropy such as birefringence or dichroism in thin films.

^ Fiber-based Microfabrication
P. J. A. Kenis,* E. Choban
University of Illinois

The goal of this project is to develop direct microfabrication techniques for the assembly of fiber-based microstructures. The fibers can be used either as tools that assist in the assembly by guiding the folding of microstructures, or they can become part of the microstructures, as is the case in tensegrity structures or extendable beams. Another direction involves the integration of microelectronic components in textiles (so-called electro-textiles). In order to connect and integrate the different electronic components, patterning of leads on or in the fibers is required. Applications include integrated health monitoring and communication systems in vests.

^ Ion- and Photon-enhanced Surface Diffusion
E. G. Seebauer,* E. R. Blomiley
National Science Foundation, CTS 98-06329

Recent measurements by this research team of surface diffusion on Si have demonstrated that both photon illumination and low-energy ion bombardment can significantly alter surface diffusion on Group IV semiconductors. Neither effect has ever been observed directly before. Photon-induced modifications seem to be mediated electronically, as substrate doping affects the results. Ion-induced modifications clearly involve some sort of momentum transfer. Both effects can have direct implications for semiconductor processing.

^ Laser Measurements of Thermal Surface Diffusion
E. G. Seebauer,* Z. Wang, E. R. Blomiley
National Science Foundation, CTS 98-06329; U.S. Department of Energy, DE-FG02-96ER45439

(In cooperation with the Materials Research Laboratory)

Surface diffusion on semiconductors is important in several aspects of microelectronic device fabrication. Researchers are making measurements of surface diffusion under real processing temperatures and pressures using a recently developed laser technique of second harmonic microscopy. Under such conditions, the research team has found that the diffusion mechanism changes from simple site hopping to a previously unknown vacancy-mediated form. The researchers are probing surface diffusion in a variety of adsorption systems to determine the precise nature of this mechanism.

^ Simulations of Surface Diffusion by Molecular Dynamics
E. G. Seebauer,* Z. Wang
National Science Foundation, CTS 98-06329

Researchers are performing computer simulations of surface diffusion on silicon and germanium by molecular dynamics. This approach uses selected interatomic potentials and integrates the equations of motion for an ensemble of surface atoms. Data indicate good correspondence between the simulational results and experiments for Ge on Si. Researchers are now examining the effects of low-energy ion bombardment.

^ Assembly of Nanoparticles
C. F. Zukoski,* S. Ramakrishnan
U.S. Department of Energy, DE-AC02-96ER45439

(In cooperation with the Materials Research Laboratory)

Methods of manipulating the interactions of 1-nm particles are explored. Research includes a focus on the strength of attraction of heteropolymetal oxyanions controlled through ionic strength and characterized through light scattering and viscosity. Links between the strength of attraction and anion solubility are studied. Methods of building nanoporous structures of these superacid particles are developed.

^ Drying and Cracking in Ceramic Fabrication
C. F. Zukoski,* L. Brown
U.S. Department of Energy, DE-FG02-96ER45439

(In cooperation with the Materials Research Laboratory)

Understanding the stresses built up in ceramic green bodies is essential to producing ceramics with low flaw density. In this study, researchers look at the role of interparticle forces in determining rates of drying and compaction in slurries. Conditions resulting in cracking are explored with the goal of generating dense, uniform, crack-free green bodies.

^ Flow of Weakly Flocculated Suspensions
C. F. Zukoski,* S. J. Yoon
U.S. Department of Energy, DE-FG02-96ER45439

(In cooperation with the Materials Research Laboratory)

In this investigation, researchers examine the flow properties of weakly flocculated suspensions. A model system has been chosen in which, by solution pH, the suspension can be reversibly gelled. By mapping out a phase boundary in pH/volume fraction space, the research team is able to explore the relationship between flocculation in colloidal suspensions and sol-gel transitions observed in molecular systems. The mechanical properties of the gelled samples are of importance in determining porosity and suspension processibility. Researchers are seeking general descriptions of yielding and flow in terms of the depth of the interparticle attractive potential.


Summary of Engineering Research