Droplet-Assisted Vapor Phase Polymerization for Controlling Nanostructures of Conducting Polymers

Speaker: Julio M. D’Arcy

Washington University in St. Louis

The D’Arcy laboratory develops vapor phase polymerization strategies for nanostructured conducting polymers and investigates fundamental structure-property relationships of low dimensional organic electronics for electrochemical energy storage applications. Here, a droplet-assisted vapor phase polymerization (DVPP) strategy is presented that results in low dimensional structures of conducting polymers such as nanofibers, nanowires and microtubes without the use of templates. In DVPP, monomer vapor is oxidized by an aqueous droplet of a ferric chloride solution, this initiates oxidative radical polymerization and promotes step-growth assembly of a conjugated polymer backbone. Water evaporation and condensation processes, that stabilize the three-phase solid-water-air interface present on a resting droplet, control polymerization kinetics. Moreover, concentration, temperature, pH, and the rate of mass transfer of reactant vapors are chemical handles that lead to conducting polymer nanostructures with high electronic conductivity and superior electrochemical stability. Grafting on aromatic groups present on a hard carbon fiber substrate is carried out by Friedel-Crafts alkylation using iron chloride as a catalyst and nitromethane as a catalyst activator. Poly(3,4-ethylenedioxythiophene) grafted on carbon fiber current collectors affords electrochemical capacitors retaining 90% of their initial capacitance over 350,000 cycles in 1 M H2SO4 at 5 A/g current density in a 1 V window. Low temperature DVPP deposits polypyrrole nanobrushes and pseudocapacitors that undergo 200,000 cycles while retaining 70% of their initial capacitance. Droplets, serving as templates in our syntheses, result in pseudocapacitive conformal coatings of polypyrrole microtubes with a sheet resistance of 70.2 ohm/sq.; these produce a mechanically robust electrode architecture characterized by a high reversible capacitance of 342 F/g throughout 5,000 cyclic voltammetric cycles.