Characterizing Water Interactions at the Surface of Carbon Char Microparticles - Surface Science and Oximetry
Dr. R.B. Clarkson
Illinois EPR Research Center
Wednesday, April 29, 1998 3:30 pm
Ben Bandy Conference Center
Center for Applied Energy Research
Synthetic carbon char microparticles (d < 20 µm) are being developed as paramagnetic sensors for the measurement of oxygen levels in living tissues, foods, materials, and other applications which require fast, non-invasive monitoring of po2. These particles usually are porous, with a distribution of pore sizes, and a surface area which is typically in the range of 100 - 500 m2/gram. Interactions of these particles with water (and other liquids) is the key to their suitability for sensor applications. We have studied water interactions at the surface and in the porous structure of carbon char particles, making use of a variety of magnetic resonance methods, including electron paramagnetic resonance (epr), nuclear magnetic resonance (nmr), and dynamic nuclear polarization (dnp). The surface interactions often can be observed by measuring the effects on electron and nuclear spin relaxation. We will present information on the interactions of oxygen and water at the surface of the particles, and will show how solvent dynamics can be followed, making use of dnp and 1h gradient echo nmr methods. The pore structure is hypothesized to trap water molecules and promote positive dnp effects, which indicate the overlap of unpaired electrons between the particle surface and water protons. This work is supported in part by grants from the nih (gm51630, rr01811) and the doe (de fg22-96pc 96205).