Real-Time Polypyrrole Electrodeposition Kinetics Monitored by Surface Plasmon Resonance: Impact of the Deposition Method and Dopamine Copolymerization.

The modification of surfaces with conductive polymers, such as polypyrrole, creates functional materials that can be applied in a wide range of fields. To optimally utilize polypyrrole materials, in particular those produced through electrodeposition, we require knowledge of film properties and how these are affected by the deposition technique. In work done by others, the focus is mostly on the layer properties that are achieved and not on the early stages of synthesis that ultimately determine these properties. Here, we evaluate the role of electrodeposition techniques and dopamine on the early stages of polymerization kinetics of polypyrrole thin films (<30 nm) through real-time analysis with surface plasmon resonance (SPR). Electrochemical polymerization was performed through galvanostatic, potentiostatic, pulsed galvanostatic, and pulsed potentiostatic deposition, varying the applied current or potential, in the absence and presence of dopamine. The results reveal that the polymerization speed is technique-dependent and connected to the measured potential or current. Polymerization is limited by pyrrole radical formation, which can be partially mitigated by reaching the threshold potential (±0.4 V). The polymerization speed increases over the synthesis time due to the decreasing oxidation potential of larger pyrrole structures. Dopamine copolymerization catalyzes the initial pyrrole radicalization but shifts the polymerization location from surface- to solution-based, therewith reducing the polymerization speed on the surface. The investigated deposition conditions resulted in pronounced differences in composition, structure, thickness, and visual appearance of the films. The real-time evaluation carried out in this paper provides insights into the effect of the deposition technique and dopamine on the initial polymerization reactions, polymerization speed, and controllability. Connecting these insights in polypyrrole polymerization with film properties is essential for the utilization of polypyrrole as a smart material in various fields, e.g., sensors, batteries, or biomaterials.