In-Situ Imaging of Polymer and Organic Molecular Materials by Transmission Electron Microscopy

We have been examining the use of in-situ techniques for monitoring the oxidative electrochemical polymerization of conjugated polythiophenes such as poly(3,4-ethylene dioxythiophene) (PEDOT) using transmission electron microscopy (TEM). Our approach utilizes a thin (~500 nm) film of reactive EDOT monomer-containing liquid sandwiched between a bottom substrate with microfabricated working, reference, and counter electrodes; and a solid top film. The electron dose must be carefully controlled and monitored during imaging to avoid damage to the sample and artifacts such as bubble formation. The method allows for the direct visualization of the transition from liquid EDOT monomer, through viscoelastic oligomers, to the final solid PEDOT polymer product. The detailed size, shape, and distribution of the precipitating intermediate states can be resolved, revealing new information about the local mechanisms of electrodeposition. This includes the evaporation of previously formed droplets back into the solution, presumably by curvature-driven variations in solubility similar to Ostwald ripening. Complimentary information about the processes seen in TEM can be obtained by a variety of other techniques including optical microscopy, scanning electron microscopy, and spatially-resolved infrared and Raman spectroscopies.