title: Long-Term Repellency of Liquids by Superoleophobic Surfaces.
abstract: Applications of superoleophobic surfaces depend on the stability of the air cushion formed under liquid drops. To analyze the longevity of air cushions we used reflection-interference contrast microscopy (RICM) for drops on a porous fractal-like structure of sintered nanoparticles. RICM permits us to monitor the height of the air cushion with nanometer resolution. Whereas the air cushion under all investigated liquids was stable on a time scale of a few seconds to minutes and liquids rolled off, liquids with low surface tension penetrated the coating on the time scale of hours and longer. The penetration speed showed a power law dependence on time, dz/dt∼t^{p}, the exponent p varying from -0.5 to -1.2. Thus, penetration is qualitatively different from the Lucas-Washburn law that governs spontaneous capillary filling of porous structures.
authors: Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany.
authors: Periklis
authors: P
authors: Papadopoulos
authors: Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany.
authors: Doris
authors: D
authors: Vollmer
authors: Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany.
authors: Hans-Jürgen
authors: HJ
authors: Butt