The role of dissolved gas in longevity of Cassie states for immersed superhydrophobic surfaces

We report on the longevity of dewetted (Cassie) states on submerged superhydrophobic (SHPo) surfaces in relation to dissolved ambient gases in the water. The report uniquely verifies that trapped gas on a submerged SHPo surface is lost faster, i.e., the surface becomes wetted faster, if the surrounding water contains less dissolved gas. This study improves on previous SHPo characterization methods by processing time-lapse images to calculate wetted surface fractions. Teflon^®-coated SHPo grating samples with parallel ridges 10 μm in width, 50 μm in pitch (i.e., 80% gas fraction), and 50 μm in depth are submersed vertically 10 cm deep in gas-concentration-controlled DI water. SHPo surfaces immersed in degassed water wetted more rapidly than in equilibrated or supersaturated water, and all surfaces failed within a finite time period indicating the challenges of underwater SHPo applications.