The current methods for catalyst regeneration produce small amounts of dioxin. The objective of this project is to see if we can develop a method to regenerate catalysts using a chelation scheme. Results so far indicate that we can etch metal particles using a variety of chelating agents and then convert and redeposit the metal to produce a redispersed catalyst. Current research considers how the nature of the chelating affects the binding process and the rate of catalyst redispersion.

The objective of this project is to use single-crystal catalysts to produce especially active sites for a variety of catalytic reactions. We have discovered sites for the treatment of automotive exhaust, the conversion of methanol to formaldehyde and the conversion of alcohols to hydrocarbon fuels. We are currently exploring sites for the hydrocarbon reforming.

Analyses of the conformational dynamics and rheo-optical behavior of semiflexible macromolecules are investigated using Brownian dynamics. Calculations are based on a discrete version of the wormlike chain model, extended to include torsional degrees of freedom and hydrodynamic flow. Calculations for rheological (stresses, viscometric functions) and optical quantities (birefringence, dichroism, light scattering) are done for steady and transient flows. The role of flexibility in the transient overshoot and relaxation behavior are emphasized. Molecular dynamics simulations are also used to obtain realistic potentials for the bending and torsional effects for comparison to experiments.

The effects of shear flow, temperature, and pH on secondary structure, conformational states, and phase stability of macromolecules in the solution state are investigated using modulated polarimetry and laser Raman spectroscopy. Molecules include those with charged side groups, of which poly-L-lysine (PLL) is a model, and those with uncharged side groups, of which poly-;gg-benzyl-L-glutamate (PBLG), poly-;g9-CBZ-L-lysine (PCBL), and hydroxypropyl cellulose (HPC) are examples. Flow birefringence and optical rotatory power are used to probe molecular rigidity changes when conditions of temperature and solvent environment are varied.

Models of flow-induced crystallization are developed based on theories of nucleation-controlled and strain-induced crystallization, coupled with the irreversible thermodynamic formalism of the continuum Hamiltonian brackets. Model analyses include the effects of relaxational and orientational processes as well as simultaneous deformation histories on the crystallization kinetics in terms of molecular relaxation times, a crystallization parameter, and the melt molecular weight. Calculations of the crystallization rate, chain elongation, stress, and birefringence are done for a variety of flow kinematic histories, including transient flow. Results are compared to experimentally observed trends reported in the literature.

We are developing quantitative models to describe the mechanisms involved in membrane structure formation by phase inversion of polymer solutions. Experiment and theory are being pursued for both the nonsolvent and thermal quench processes. The former involves optical techniques we developed for the measurement of mass transfer and gelation rates and comparison to models based on ternary diffusion formalisms. The latter involves measurements of small-angle scattering behavior in thermally quenched films and comparison to models for phase transformation by spinodal decomposition and nucleation and growth. Both experiments also involve analyses of film morphologies by scanning electron microscopy.

The rheological and processing behavior of fiber-filled macro-defect-free (MDF) cement pastes are studied. Rheological studies focus on measurements of the extensional viscosity and nonlinear relaxation behavior in equibiaxial flows. Processing of fiber-filled pastes is being carried out in a Banbury-type mixer. The objective is to quantify the relationship between paste chemistry, mixing history, and final composite properties.

The compaction of cementitious systems controls weeping phenomena, aggregate settling, and formation of uniform coatings in spin casting of cementitious pipe linings. In this project, we investigate compressive properties of cements and other weakly flocculated suspensions. Links are sought between compressive and shear yield stresses. In addition, the influence of vibrations in aiding compaction is under study.

Denotes principal investigator.

Photo Caption:

Professor Deborah Leckband watches as graduate student Shailesh Sheth uses a surface force apparatus to measure the molecular level interactions between proteins and biomedically important polymers.

Photo Caption:

Professor Richard Braatz (standing) examines the results of graduate student Evan Russell's latest algorithm for the analysis and synthesis of large-scale robust optimal controllers.

Photo Caption:

Graduate student Diana Llera-Rodriguez rotates a silicon sample, mounted in an ultrahigh vacuum chamber, into position for performing second harmonic microscopy. She uses this technique for quantifying surface diffusion on semiconductors, including investigating the effects of photon and ion beams on the diffusivities.

Photo Caption:

Graduate student Bill Hunt characterizes the surface charge density of 200-nm-diameter spheres suspended in aqueous electrolyte solutions using an automated electrophoresis instrument.

Photo Caption:

Using a Banbury mixing device, graduate student Andrew Walberer carries out studies on the dynamics of structure formation in polymer-cement composite materials.