Direct Observation of Liquid-to-Solid Phase Transformations during the Electrochemical Deposition of Poly(3,4-ethylenedioxythiophene) (PEDOT) by Liquid-Phase Transmission Electron Microscopy (LPTEM)

We have used liquid-phase transmission electron microscopy (LPTEM) to directly image the fundamental processes occurring at the electrode-solution interface during the electro-chemical deposition of poly(3,4-ethylenedioxythiophene) (PEDOT) from an isotropic 3,4-ethylenedioxythiophene (EDOT) monomer solution. We clearly observed the various stages of the electrodeposition process including the initial nucleation of liquid-like EDOT oligomer droplets onto the glassy carbon working electrode and then merging, coalescence, and growth in size and thickness of these droplets into solid, stable, and dark PEDOT-conjugated polymer films. We also used correlative transmitted light optical microscopy to study this process, revealing the change in the color of the translucent clusters to the dark polymer film caused by the increase in conjugation length. From our studies, we have been able to correlate specific observations of local structure and dynamics to the liquid-like (EDOT oligomer) droplets and solid-like (PEDOT polymer) films including their mobility, mass thickness, edge roughness, size, circularity, and optical absorption.