Junyan Yang

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.

Electrochemical fabrication of conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) nanofibrils on microfabricated neural prosthetic devices.

This paper describes methods for electrochemically polymerizing conducting polymer poly(3,4-dioxyethylenethiophene) (PEDOT) nanofibrils on microfabricated neural prosthetic devices from aqueous solutions containing polyacrylic acid (PAA). These fibrils have characteristic sizes ranging from 100 to 1000 nm in diameter, depending on the concentration, molecular weight of PAA and thickness of the film. The PEDOT nanofibril-coated electrodes have significantly lower electrical impedance due to their higher effective surface area. We propose a mechanism of nanofibril formation involving locally anisotropic variations in EDOT monomer transport and PEDOT film growth due to segregation of the PAA counter-ions. This deposition method provides an improvement in the electrical properties by increasing the effective surface area of the electrodes, while still maintaining the overall small electrode size. It is also opens up new reliable and reproducible strategies for the direct electrochemical polymerization of conducting polymer nanofibrils on a variety of electrodes.

Electrochemical Polymerization of Conducting Polymer Coatings on Neural Prosthetic Devices: Nanomushrooms of Polypyrrole Using Block Copolymer Thin Films as Templates

We have demonstrated a method to rapidly and reliably fabricate arrays based on the self-assembled morphology of block copolymer ultra thin films. An ordered, nanoporous structure obtained from the block copolymer thin films is used a template for the subsequent electrodeposition of conducting polymer nanomushrooms of polypyrrole (PPy). The influence of current density, deposition charge and morphology of the templates and nanostructured conducting polymer coatings has been investigated. The electrical properties of the polymer coatings were studied.