LOCALIZED PARAMAGNETISM IN CARBON-BLACKS - INHERENT VS ELECTROCHEMICALLY REDUCED SITES

The results of an electron paramagnetic resonance investigation of four different carbon blacks are presented. These include an oxidized, a devolatilized and a surface-modified black. All of these blacks manifest a narrow EPR signal at low temperatures. This signal, referred to as the inherent signal, has an intensity which correlates with the number of functional groups on the surface. Electrochemical reduction of these four blacks also yields narrow EPR signals but with intensities approximately 1 order of magnitude greater than their corresponding inherent signals. The magnitude of these electrochemically generated signals also correlates with the number of surface functionalities. A temperature study of both the inherent and electrochemical EPR signals reveals that these paramagnetic sites are most likely localized. This is deduced from the fact that below 185 K, the Curie law is followed. Over 185 K the inherent signal is exponentially dependent on the temperature, suggesting a Boltzmann-type equilibrium between charge carriers and surface states.