Redox properties, on the other hand, are measured in electrochemical cells that are essentially half of a battery. Voltage and the amount of current flowing through the primary electrode depend on the reaction redox potential and the concentration of the test material.
The problem, Prabhu explains, is that SANS measures things in bulk, in a volume of space, but, "An electrochemical experiment is a very local experimentit happens at an interface. What we needed was to maximize the interface." The answer, contributed by his partner, Vytas Reipa, is an exotic material called reticulated glassy carbon. "Like a very stiff household sponge or scouring pad made of pure carbon," Prabhu explains. The porous carbon electrode turned out to be an ideal terminallots of surface area to serve as a reaction interface; nearly transparent to neutrons, so it doesn't contribute much background noise; and best of all, it works well in water, enabling the study of nanoparticles in aqueous solutions, critical for biological reactions.
A big advantage of the "eSANS" technique, Prabhu says, is its generality. "You can apply our method to nearly any dispersed material that is of interest to redox chemistrypolymers, redox proteins, nucleic acidsat this nanoscale. Small polymer chains, for example. You can't really see them with electron microscopy, you can with neutrons."
|Contact: Michael Baum|
National Institute of Standards and Technology (NIST)