The Effect of Ferric Chloride on Charge Injection into Polyethylene
DC charge injection from aqueous electrolytes into low density polyethylene was investigated. Among the electrolytes surveyed, it was found that much higher current densities were recorded when solutions containing both ferric ions and chloride ions were electrochemically oxidized at the polyethylene interface. It was found that exposure to ferric chloride solutions both with and without applied voltage rendered the polyethylene susceptible to charge injection from other solutions that did not contain ferric and chloride ions. Characterization with electrochemical impedance spectroscopy of polyethylene after the application of voltage in the presence of ferric chloride electrolytes did not reveal significant changes, but oxidation products on the exposed surface of polyethylene were detected by both fluorescence spectroscopy and X-ray photoelectron spectroscopy. The effect of oxidation of the surface of polyethylene on charge injection is investigated.
A mechanism of the action of the ferric chloride solutions is proposed by which complexes of ferric ions and chloride ions catalyze the oxidation of a component in the electrolyte. The electron produced by this oxidation reaction is injected into a surface state in the polyethylene. The identity of the complex in ferric chloride solutions responsible for this catalytic behavior is believed to be FeCl4-. The presence of atmospheric oxygen in the electrolyte is thought to be necessary for the production of the oxidation groups on the surface of polyethylene that lead to enhanced charge injection with other electrolytes.