Nanoscale analysis of functionalized polythiophene surfaces: the effects of electropolymerization methods and thermal treatment

Functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) thin films fabricated by cyclic voltammetry and potentiostatic electropolymerization were analyzed by adhesion mapping. Two monomers, zwitterionic phosphorylcholine EDOT (EDOT-PC) and hydroxymethyl EDOT (EDOT-OH), were used to prepare the corresponding homopolymers PEDOT-PC and PEDOT-OH. Force-extension curve-based atomic force microscopy (AFM) was used to generate nanoscale-resolution maps revealing the characteristic stretching behavior at each pixel. As expected, the maps for PEDOT-PC consisted mostly of pixels with long stretching curves, whereas the maps for PEDOT-OH consisted of pixels with short stretching curves. The number of pixels with short stretching curves was compared with the number of pixels with long stretching curves. For PEDOT-PC, the relative ratio of the pixels with long stretching increased with the rate of voltage change (or number of cycles) during electropolymerization. The relative ratio of short to long stretched pixels in the film fabricated by potentiostatic electropolymerization was as large as that of the film fabricated by cyclic voltammetry at the highest scan rate (400 mV s(-1)). The thermal annealing increased the number of pixels with short stretching, indicating that chain reorganization led to stronger interchain adhesion. For PEDOT-OH, the films were composed primarily of pixels with short stretching. The relative short to long stretching ratio was insensitive to the polymerization method. Our approach can be used to resolve the surface structure of polymer films at the nanoscale.