The Morphology of Poly(3,4-Ethylenedioxythiophene)

Poly(3,4-ethylene dioxythiophene) (PEDOT) is a chemically stable, conjugated polymer that is of considerable interest for a variety of applications including coatings for interfacing electronic biomedical devices with living tissue. Here, we describe recent work from our laboratory and elsewhere to investigate the morphology of PEDOT in the solid state. We discuss the importance of oxidative chemical and electrochemical polymerization, as well as the critical role of the counterion used during synthesis and film deposition. We have obtained information about the morphology of PEDOT from a number of different complimentary techniques including X-ray diffraction, optical microscopy, scanning electron microscopy, transmission high-resolution electron microscopy, and low-voltage electron microscopy. We also discuss results from ultraviolet-visible light spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). PEDOT is a relatively rigid polymer that packs in the solid state at a characteristic face-to-face distance (010) of 0.34 nm, similar to graphite. These sheets of oriented PEDOT molecules are separated from one another by 1.4 nm laterally, with the (100) distance between layers quite sensitive to the choice of counterion used during sample preparation. The order in the films is typically modest, although this also depends on the counterion used and the method of film deposition. The films can be organized into useful structures with a variety of nanoscale dissolvable templates (including fibers, particles, and lyotropic mesophases). When PEDOT is electrochemically deposited in the presence of bromine counterions, highly ordered crystalline phases are observed. It is also possible to deposit PEDOT around living cells, both in vitro and in vivo.