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Micromachines 2018, 9(11), 566; https://doi.org/10.3390/mi9110566

Trapping a Hot Drop on a Superhydrophobic Surface with Rapid Condensation or Microtexture Melting

Department of Mechanical Engineering, Boston University, Boston, MA 02215, USA
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Received: 9 October 2018 / Revised: 24 October 2018 / Accepted: 30 October 2018 / Published: 2 November 2018
(This article belongs to the Special Issue Microscale Surface Tension and Its Applications)
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Abstract

A water drop can bounce upon impacting a superhydrophobic surface. However, on certain superhydrophobic surfaces, a water drop will stick rather than bounce if it is sufficiently hot. Here, we aim to better understand the mechanisms that can lead to this bouncing-sticking transition. Specifically, we model two potential mechanisms in which a superhydrophobic surface could trap a sufficiently hot drop within milliseconds: melting of microtextured wax and condensation of the vapor within the superhydrophobic texture. We then test these mechanisms through systematic drop impact experiments in which we independently vary the substrate and drop temperatures on a waxy superhydrophobic Nasturtium leaf. We find that, whenever the surface or the drop is above a microtexture-melting temperature, the drop sticks. Below this temperature, a critical temperature threshold for bouncing can be predicted and controlled by considering the relative timescales between condensation growth and drop residence time. We envision that these results can provide insight into the design of a new class of superhydrophobic surfaces to act as a rapid thermal fuse to prevent drops that exceed a critical temperature from bouncing onto a thermally sensitive target. View Full-Text
Keywords: Nasturtium leaf; smart superhydrophobic surface; hot drop; condensation; microtexture melting Nasturtium leaf; smart superhydrophobic surface; hot drop; condensation; microtexture melting
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Shiri, S.; Murrizi, A.; Bird, J.C. Trapping a Hot Drop on a Superhydrophobic Surface with Rapid Condensation or Microtexture Melting. Micromachines 2018, 9, 566.

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