Layer-by-layer assembly of electrically conductive polymer thin films

Abstract

Layer-by-layer (LbL) assembly was used to produce highly conductive thin films with carbon black (CB) and polyelectrolytes. The effects of sonication and pHadjustment of the deposition mixtures on the conductivity and transparency of deposited films were studied. Drying temperature was also evaluated with regard to thin film resistance. Sonication and oven drying at 70oC produced films with the lowest sheet resistance (~ 1500 Ω/sq), which corresponds to a bulk resistivity of 0.2 Ω⋠cm for a 14- bilayer film that is 1.3 μm thick. Increasing the pH of the PAA-stabilized mixture and decreasing the pH of the PEI-stabilized mixture resulted in films with 70% transparency due to thinner deposition from increased polymer charge density. Varying the number of bilayers allows both sheet resistance and optical transparency to be tailored over a broad range. Variation of deposition mixture composition led to further reduction of sheet resistance per bilayer. A 14 bilayer film, made from mixtures of 0.25wt% carbon black in 0.05wt% PAA and plain 0.1wt% PEI, was found to have a sheet resistance of approximately 325 Ω/sq. Bulk resistivity was not improved due to the film being 8 μm thick, but this combination of small thickness and low resistance is an order of magnitude better than carbon black filled composites made via traditional melt or solution processing. Applications for this technology lie in the areas of flexible electronics, electrostatic charge dissipation, and electromagnetic interference shielding.