Electrochemical deposition and characterization of carboxylic acid functionalized PEDOT copolymers

Conjugated polymer films are of considerable current interest for functionalizing the surfaces of a wide variety of devices including implantable biomedical electronics. Toward these ends, copolymer films of 3,4-ethylenedioxythiophene (EDOT) with a carboxylic acid functional EDOT (EDOTacid) were electrochemically deposited and characterized as a systematic function of the EDOTacid content (0, 25, 50, 75, and 100%). Chemical surface characterization of the films confirmed the presence of both EDOT and EDOTacid units. Toluidene blue assays showed that the surface concentration of the carboxylic acid groups increased to a maximum of 2.75 nmoles/mm2, and the contact angle measurements confirmed the increased hydrophilicity of the films with increasing EDOTacid content (decreasing from 52.6 to 32.5 degrees). Cyclic voltammetry showed that the films had comparable charge storage capacities regardless of their composition. The morphology of the films varied depending on the monomer feed ratio. The addition of EDOTacid induced a transition from a nodular, porous surface to a more dense, pleated surface structure. These methods provide a facile means for synthesizing electrically active carboxylic acid functional poly(3,4-ethylenedioxythiophene) copolymer films with tunable hydrophilicity and surface morphologies.