James J. Watkins

Current Focus of Research

In our research program, fundamental issues in chemistry, transport phenomena, phase equilibria and kinetics are addressed with the goals of applying the results to the development of new materials and advanced processing techniques. Areas of interest include polymers, electronic materials, and supported catalysis. Current focus is on the use of supercritical fluid (SCF) solvents such as carbon dioxide in materials processing. The key features of SCFs are the strong temperature and pressure dependences of their physicochemical properties (density, dielectric constant, viscosity) and the environmentally benign characteristics of solvents.

Chemical Fluid Deposition

The deposition of thin solid films at low temperatures is a critical issue in the microelectronics industry. Chemical Fluid Deposition (CFD), a process by which high-purity metals are deposited by the reduction of organometallic precursors in SCF CO₂ solution, is under development in our laboratories. CFD uniquely combines the capability of depositing high-quality films typically associated with vapor-phase techniques (e.g., chemical vapor deposition, CVD) with the benefits of a solution-based process. These benefits include low temperatures, clean chemistry, and elimination of the CVD requirement of reagent volatility. Target applications include copper and semiconductor thin film depositions on inorganic and polymer substrates.
We are also studying the preparation of supported catalysts and nanostructured materials by CFD. The transport properties of SCFs (low viscosity, zero surface tension) are ideal for depositions within microporous substrates, including inorganic membranes.

Transport Properties and Reaction Kinetics in SCF/Polymer Systems

We are investigating the synthesis, modification and processing of polymers in SCF CO₂. Since the vast majority of these processes are heterogeneous, process dynamics are often dominated by transport in the SCF-swollen polymer. In this study, we employ in situ spectroscopic and chromatographic techniques to determine diffusion rates of solvent, small molecule penetrants (e.g., reagents) and polymer chains as a function of volume fraction of CO₂ dissolved in the polymer. In combination with kinetic data, the results are used to determine the effects of mass transfer on reaction kinetics in these systems.

Polymer Processing and Chemistry in SCF CO₂-Swollen Polymer Melts

The dramatic decrease in viscosity and increases in both polymer chain and penetrant diffusion rates upon plasticization of polymers with CO₂ greatly expands the range of melt phase chemistry that can be practiced in conventional, high-pressure extruders. Reactions we are investigating include bulk condensation polymerizations (where CO₂ is used to remove condensate as well as a plasticizer to promote high molecular weight) and blend compatibilization reactions. The technique is a potential alternative to organic solvent-based processing methods.

Selected Publications
Pai, R. A..; Humayun, R.; Schulber,M.T.; Sengupta, A.; Sun, J-N; Watkins, J. J. "Mesoporous Silicates Prepared Using Preorganized Templates in Supercritical Fluids" Science, 2004 303: 507-510.

Gupta, R.R.; RamachandraRao, V.S.; Watkins, J.J. "Measurement of Probe Diffusion in CO₂-Swollen Polystyrene Using in situ Fluorescence Nonradiative Energy Transfer" Macromolecules, 2003, 36, 1295.

Vogt, B.D.; RamachandraRao, V.S.; Gupta, R.R.; Lavery, K.A.; Francis, T.J.; Russell, T.P.; Watkins, J.J. "Phase Behavior of Polystyrene-block-Poly(n-Alkyl Methacrylate)s Dilated with Carbon Dioxide" Macromolecules, 2003, 36, 4029.

Cabanas, A.; Shan, X.; Watkins, J.J. "Alcohol-assisted Deposition of Copper Films from Supercritical Carbon Dioxide" Chemistry of Materials, 2003, 15, 2910.

Blackburn, J.M.; Long, D.L.; Cabanas, A.; Watkins, J.J. "Deposition of Conformal Copper and Nickel Films from Supercritical Carbon Dioxide" Science, 2001, 294-141.