72th Annual Meeting of the APS Division of Fluid Dynamics (November 23, 2019 — November 26, 2019)

V0040: Crystal Critters

  • Samantha McBride, MIT
  • Henri-Louis Girard, MIT
  • Kripa Varanasi, MIT
DOI: https://doi.org/10.1103/APS.DFD.2019.GFM.V0040

When a drop of salty water is evaporated on a hydrophobic surface, “salt globes” that mirror the shape of the drop grow. Here, we present an unusual phenomenon in which salt globes grown from an evaporating drop on a heated superhydrophobic surface proceed to self-eject from that surface via growth of crystalline tubules. A large temperature gradient concentrates vaporization near the substrate, and escaping vapor at contact points between substrate and liquid leads to growth of crystalline tubules. These tubules grow into "legs," causing the entire salt globe – and any remaining water – to lift off from the surface. We call the structures composed of salt globes balanced on tubule legs “crystal critters” due to their resemblance to biological forms. Following complete evaporation, the crystal critters have minimal contact with the substrate and can be easily removed; and could find application for anti-fouling surfaces for spray heat exchangers.

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