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Morphing and vectoring impacting droplets by means of wettability-engineered surfaces

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posted on 04.03.2016 by T.M. Schutzius, G. Graeber, M. Elsharkawy, J. Oreluk, Constantine M. Megaridis
Driven by its importance in nature and technology, droplet impact on solid surfaces has been studied for decades. To date, research on control of droplet impact outcome has focused on optimizing pre-impact parameters, e.g., droplet size and velocity. Here we follow a different, post-impact, surface engineering approach yielding controlled vectoring and morphing of droplets during and after impact. Surfaces with patterned domains of extreme wettability (high or low) are fabricated and implemented for controlling the impact process during and even after rebound —a previously neglected aspect of impact studies on non-wetting surfaces. For non-rebound cases, droplets can be morphed from spheres to complex shapes — without unwanted loss of liquid. The procedure relies on competition between surface tension and fluid inertial forces, and harnesses the naturally occurring contact-line pinning mechanisms at sharp wettability changes to create viable dry regions in the spread liquid volume. Utilizing the same forces central to morphing, we demonstrate the ability to rebound orthogonally-impacting droplets with an additional non-orthogonal velocity component. We theoretically analyze this capability and derive a We2.25 dependence of the lateral restitution coefficient. This study offers wettability-engineered surfaces as a new approach to manipulate impacting droplet microvolumes, with ramifications for surface microfluidics and fluid-assisted templating applications.

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GG was supported by a DAAD-RISE Internship Award during the summer of 2012. TMS acknowledges Prof. Ranjan Ganguly (Jadavpur University) for useful discussions. We thank PChem Associates, Inc. for providing the silver ink. M.E. was supported by a National Science Foundation Graduate Research Fellowship under Grant No. 0907994.

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Publisher Statement

This is the copy of an article published in Scientific Reports ©2014 Nature Publishing Group. Scientific Reports. 2015. 4: 7029. DOI: 10.1038/srep07029. © The Author(s). www.nature.com/scientificreports

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Nature Publishing Group

issn

2045-2322

Issue date

13/11/2014

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