Micro/Nano-Structured Polypyrrole Surfaces on Oxidizable Metals as Smart Electroswitchable Coatings

Polypyrrole (PPy) films were electrodeposited from a pyrrole/sodium salicylate solution in water, through two-dimensional (2-D) polystyrene (PS) templates self-assembled on various oxidizable metals, after which the template was removed by dissolution in tetrahydrofuran (THF). The resulting PPy films were analyzed by scanning electron microscopy and atomic force microscopy. Two-dimensional PPy honeycomb structures are obtained on copper or mild steel by using PS spheres of various sizes. The morphology of these structures was controlled electrochemically, as an increase in the polymerization charge does not disturb the PPy honeycomb arrangement, leading instead to the formation of deeper pores accompanied by a change in their diameter. The hydrophobicity of the reduced micro-structured PPy surface is much greater than that of a bulk PPy film generated on the same metal. Reversible electro-switching of the wettability was obtained with marked variation of the apparent contact angle upon PPy oxido-reduction, and an important effect of film micro-structuration upon the wettability range.