Wetting Transitions on Post-Built and Porous Reliefs

A comparative study of wetting transitions on porous and post-built polymer surfaces is reported. The transitions were observed under vibration of droplets of different volumes deposited on the surfaces possessing controlled roughness. Initial wetting states were identified as the Cassie air-trapping ('Fakir') state for porous and the Wenzel state for post-built relief, whereas the final wetting state was the Cassie impregnating one for both kinds of surfaces. For both porous and post-built surfaces, wetting transitions occurred under constant force acting on a unit length of the three-phase (triple) line. Wetting transitions for both porous and post-built surfaces start from the triple line. (C) Koninklijke Brill NV, Leiden, 2012