Electric field induced dewetting and pattern formation in thin conducting polymer film

Electric field induced instability and two-dimensional sub-micropattern formation in thin films of polyaniline (PANi) (conducting polymer (CP)) at different levels of doping with camphor sulfonic acid (CSA) are studied experimentally. Optical microscopic and AFM analysis reveal that the application of electric field across the thin PANi-EB (emeraldine base) film-air interface between two electrodes causes instability and formation of uniformly dispersed sub-micron column/drop like elevations surrounded by annular depression. The number density and height of such pattern increase with voltage increment. Number density analysis reveals that below a threshold voltage, CP (at its base state) behaves like a dielectric polymer. On the contrary, a 50% doped PANi-ES (emeraldine salt) thin film-air interface forms stripe like on-plane pattern instead of columnar patterns while subjected to electric field. Performance study reveals faster response of columnar morphology of PANi-EB while exposed to HCl vapor compared to that of thin films of PANi-EB. The significance is in design of chemical vapor sensor of low diffusional resistance utilizing high surface to volume ratio. (C) 2009 Published by Elsevier B.V