Combined Electrochemical, Ellipsometric and Microgravimetric Study of Ion Permeable Polydopamine Films

Abstract

The facile deposition of polydopamine on virtually any material and its recognized adhesive properties justify its extensive application in the biomedical field. However, these films are heterogeneous, poorly conductive and impermeable to many small molecules and ions, limiting their use in electrochemical applications. Hereby, we have potentiodynamically grown polydopamine films on gold using an anodic potential limit of 1.1 V, higher than the typically used values (0.5−0.8 V), aiming at preparing thick and permeable films. The mass increment during the electropolymerization of dopamine undergoes an abrupt change upon the 20th potential cycle, forming a more porous coating, compared to the polymer grown up to 0.8 V. By modelling in situ ellipsometric data, the abrupt phenomenon could be related to a temporary and local loss of polymer adherence to the surface, with the creation of a very porous layer, that is fulfilled in the subsequent cycles with new polymer fibers. Consequently, drastic topographic changes are depicted in polymers grown with 20 and 100 cycles, by atomic force microscopy. Films prepared with 100 cycles are thicker, more electroactive and more permeable to ionic species, than thinner films, unraveling their potential as adhesive matrices in electrochemical transduction devices.