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The influence of oxidation state on the permeability of several probe molecules through conducting polymer membranes comprising composites of poly(aniline) and poly(styrenesulfonate) was examined in aqueous solution. Pure poly(aniline) membranes displayed a characteristic increase in permeability between reduced and half-oxidized states for neutrally charged phenol and negatively charged 4-hydroxybenzenesulfonate. In contrast, positively charged pyridine experienced decreased permeability through the membrane when poly(aniline) was switched from the reduced to the half-oxidized state. This behavior can be explained by a combination of oxidation-induced film swelling and the anion-exchange character of the positively charged membrane. The membrane composition was modified to include a fixed negative charge by the addition of poly(styrenesulfonate) during synthesis. The incorporation of this negatively charged component introduced cation-exchange character to the film and substantially reduced membrane permeability to 4-hydroxybenzenesulfonate in both oxidation states. In addition, increasing the fraction of poly(styrenesulfonate) in the membrane served to decrease film permeability for all species because of a densification of the membrane. This work demonstrates how both film composition and oxidation state can be used to tune the permeability of conducting polymer membranes.
Light-emitting electrochemical cells (LECs) based on Ru(bpy)3(ClO4)2 are thin-film solid-state devices
that typically operate at low applied voltages and show relatively high efficiencies. They suffer, however,
from poor operating lifetimes. A proposed source of lifetime degradation is water in the film. Previous
studies have revealed a marked difference in operation performance between cells fabricated and tested
inside a drybox and those made and tested under ambient conditions. This study further characterized
the effect of water vapor on device operation. The role of water as solvent within the thin-film devices
was found to increase the current and the initial light output, but at the expense of more rapid decay in
light generation.
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