Halogen-Free Methods for Catalyst Regeneration
R. I. Masel,* L. Nigg, A. Shah
National Science Foundation, CTS 95-02141

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.

Intrinsic Barriers as a Guide to Mechanisms of Reactions on Solid Surfaces
R. I. Masel,* P. Blowers, L. Farmer, J. Ackerman, C. Lee
National Science Foundation, CTS 96-10115

The objective of this project is to see if one can use simple design rules based on something called an intrinsic barrier to predict the mechanisms of reactions on metal catalysts. Ab initio calculations are being used to develop correlations for barriers to reactions. The correlations are then used to predict reaction mechanisms and rates. So far we have found that we can correlate the decomposition chemistry for a wide number of dehydrogenation reactions using the method. Current work attempts to extend the method to isomerization reactions.

Rheooptics of Helical, Dendrimeric, and Hyperbranched Polymers
A. J. McHugh,* A. L. Lee
ACS PRF, Department of the Army, DAAG97-1-0126

The effects of shear flow, temperature, and solvent on conformational states and phase stability of macromolecules are being investigated using rheooptics. Birefringence shows the helix-to-coil transition in poly-l-lysine (PLL) in methanol solutions can be dramatically affected by shear. We are also investigating the role of chain architecture and branching on the rheooptics of dendrimeric and hyperbranched polymer solutions. Studies are on a polyether-imide-based system and various linear hybrids. Transient and steady birefringence, combined with a model based on a discrete version of the semiflexible, wormlike chain are used to evaluate the effects of chain architecture on molecular flexibility and dynamics.

The Rheology of Dendritic Macromolecules
A. J. McHugh,* I. Sendijarevic
Department of the Army, DAAG97-1-0126

The solution and melt rheology of dendritic molecules, including dendrimers, hyperbranched polymers, and linear hybrids are being studied. Molecules examined are available in a wide range of molecular weights with different end-groups and core functionality. Analyses of the shear stress-shear rate behavior under steady and oscillatory flows at different temperatures, solvent conditions, and concentrations are being pursued. Step shear strain experiments are employed to obtain relaxation responses. Dendrimer molecules exhibit a Newtonian behavior, while polyether amide-based HBPs, exhibit shear thinning behavior. However, in comparison to linear molecules, the viscosity of dendrimers and HBPs is significantly lower.

Continuum Modeling of Flow-induced Crystallization
A. J. McHugh,* A. Doufas
National Science Foundation, SBC Clemson, Du Pont

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.

Dynamics of Phase Inversion
A. J. McHugh,* P. D. Graham, B. F. Barton
National Science Foundation, CTS 97-31509

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.

Dynamics of Phase Inversion Related to Drug Delivery
A. J. McHugh,* J. R. DesNoyer, K. J. Brodbeck
National Science Foundation, CTS 97-31509; Alza Corp.

The principles of phase inversion are being applied in studies of injectable drug delivery systems consisting of a water-insoluble polymer, biocompatible solvent, and bioactive agent. In situ optical measurement techniques are used to quantify the interaction of liquid demixing, gelation, and drug release rates in solutions quenched into an aqueous environment. Water influx rates and bath-side mass transfer dynamics are correlated with the drug release rate and morphology of the formed gel. Systems under study include poly (lactide-co-glycolide) (PLGA) copolymers of various molecular weight and composition, a variety of biocompatible solvent systems, and model protein systems such as chicken egg lysozyme.

Structure Formation and Processing of Highly Filled Organo-Ceramic Composites
A. J. McHugh,* J. A. Walberer
NSF Center for Advanced Cement-Based Composites

Reactive organo-ceramic composites are high-strength materials formed from extrudable pastes created by high shear mixing. Torque rheometry allows monitoring the evolution of the mixing mechano-chemistry. The kinetics of structure formation are measured in four model systems that stiffen by (1) polymerization of the organic phase, (2) crosslinking of the organic phase, (3) flocculation of the ceramic phase, and (4) chemical or physical linking of the ceramic particles to the organic phase. Rheological analyses based on viscoelastic models for highly filled systems, allow analysis of the time/stress history of structuring in terms of a time-dependent modulus that follows a kinetic equation.

Kinetic Effects in Rapid Thermal Processing
E. G. Seebauer,* R. Ditchfield
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

Rapid thermal processing (RTP) constitutes an increasingly common method for oxidation, silicidation, and related steps in integrated circuit fabrication. Kinetic analysis of RTP often remains relatively crude and employs the concept of ''thermal budget.'' We are showing on experimental and theoretical grounds that this concept often yields incorrect predictions for heating programs. Instead, we are developing an alternate approach based on chemical rate selectivity.

Removal of NOx from Combustion Flues
E. G. Seebauer,* E. Blomiley
Electric Power Research Institute

We are looking at inexpensive metal oxides like Fe2O3 as candidates for photoadsorption of NOx from combustion flue gases. Photoadsorption is a novel alternative to conventional selective catalytic reduction in that no separate injection of reductant is needed. Also, the flue gas needs no reheating. Several halogen-treated oxide surfaces have shown promise.

Compressive Properties of Cementitious Systems
C. F. Zukoski,* G. Channell
National Science Foundation, CTS 95-31959

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.