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Published on: February 11, 2020
Long-Term Repellency of Liquids by Superoleophobic Surfaces
Periklis Papadopoulos1, Doris Vollmer1, Hans-Jürgen Butt1
1Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany.
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.
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