Influence of redox-induced restructuring of polypyrrole on its surface morphology and wettability

Doped polypyrrole coatings of varying degrees of wetting characteristics were prepared by a one-step anodic polymerization process and subsequently subjected to external applied potentials in an aqueous sodium benzenedodecylsulfonate solution. When an applied potential was increased from -0.9 to +0.9 at steps of 300 mV for 300 s at each step, static contact angles gradually increased from 64 degree to 122 degree . The surface morphology of as-deposited polypyrrole was observed to transform from being nodular to an increasingly rough surface composed of microscale islands with nanoscale roughness, forming a micro/nanoscale hierarchical structure. The average roughness of these microscale islands were measured to be 2.3 nm at -0.8 V, which increased to 14.6 nm at +0.8 V, compared to the average roughness of doped polypyrrole at 4.8 nm. These microscale islands were oblong in shape, and their sizes increased as the applied potential increased. Changes in the average roughness resulted in a change in the surface wettability of polypyrrole - as-deposited polypyrrole showed a static contact angle of 90 degree , however, it lowered to 70 degree at -0.8 V and irreversibly increased to 115 degree at +0.8 V.