Droplet displacement and surface cleaning with Surface Acoustic Waves

We continue the ‘Cycle of online seminars on anti-icing, de-icing and acoustic waves‘, an outreach initiative framed within the dissemination and exploitation plan of the Sound of Ice.

Prof. Michael Baudoin (University of Lille-IEMN Laboratory) will participate in this third seminar, which will be held on the 17th of May at 11:00 a.m. (CET) at the Institute of Materials Sciences in Seville and will be broadcasted online. He will give the lecture Droplet displacement and surface cleaning with Surface Acoustic Waves.

Prof. Baudoin received his Ph.D degree in acoustics and fluid mechanics from Sorbonne Université where he studied shock wave propagation and multiple scattering in suspensions of micro and nano particles. Then he joined the team of Pr. Baroud at LadHyx (Ecole Polytechnique) as a postdoc and worked on the dynamics of liquid plugs in microfluidic networks. In 2008 he started to build his own team at Université de Lille on subjects at the interface between microfluidics, acoustics and microsystems. In particular he (i) developed some miniaturized acoustical tweezers enabling the selective and contactless manipulation of microscopic particles and microorganisms, (ii) worked on the use of SAW to move droplets and clean surfaces and (iii) studied how the presence of microparticles at the interface between two immiscible fluids can drastically modify the interface behavior leading to some surprising dynamics. In 2016 he became full Professor at University of Lille and was elected Junior Fellow of Institut Universitaire de France in 2019. He also co-founded a startup, Cleardrop, on Surface Acoustic Wave (SAW)-mediated surface cleaning in 2021.

Abstract

The excitation of sessile droplets lying on a substrate with ultrasonic (MHz) Surface Acoustic Waves (SAWs) can lead to very rapid displacement of the droplets at speeds up to tens of cm per seconds [1]. The droplet displacement results from the asymmetric deformation of the drop induced by the radiation of the acoustic waves in the drop with an angle given by Snell-Descartes law and two nonlinear effects (the acoustic radiation pressure and streaming), which induce some force on the drop surface. But the droplet mobility is also strongly promoted by some low frequency (typically 100 Hz) inertio-capillary oscillations of the drop free surface [2], which unpin the contact line. How the energy is transferred from ultrasonic SAWs to surface oscillations with characteristic frequencies 5 orders of magnitude lower has long remained a mystery. After unveiling the physics behind the droplet dynamics [3,5], we will explain how this phenomenon can be used to clean surfaces. We will also show that surface acoustic waves can also be used to clean frost and ice [5], with a rich physics which remains to be understood.

[5] N. Chastrette, M. Baudoin, P. Brunet, L. Royon, R. Wunenburger*, Elucidating the oscillation instability of sessile drops triggered by surface acoustic waves, Phys. Rev. Fluids, 7: 124201 (2022)

[4] “Ultrasonic waves melting process”, submitted on 25/09/2019, application number: FR1910588, international patent WO2021058664 (Priority date: 25/09/2019 / Published  26/03/2021

[3] Bussonière, M. Baudoin*, P. Brunet and O. Bou Matar, Dynamics of sessile and pendant drop excited by surface acoustic waves: gravity effects and correlation between oscillatory and translational motions, Phys. Rev. E, 93: 053106 (2016)

[2] M. Baudoin*, P. Brunet, O. Bou-Matar, E. Herth, Low power sessile droplet actuation via modulated surface acoustic waves, Appl. Phys. Lett., 100: 154102 (2012)

[1] P. Brunet*, M. Baudoin, O. Bou Matar, F. Zoueshtiagh, Droplet displacement and oscillations induced by ultrasonic surface acoustic waves: a quantitative study, Phys. Rev. E, 81: 026315 (2010)

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