| Wed March 9th 2016 16:00 – 17:00 ZH286 | Seminar | Ultrasonic actuation of drops: inner flow and free-surface dynamics Philippe Brunet |
Details:Various analysis lab-on-chip processes require to perform elementary operations on sessile droplets, like internal mixing, translational displacement or nebulization. Surface Acoustic Waves (SAWs) propagating along a substrate can ensure all of these operations, providing the acoustic wavelength is smaller than that of the drop, which corresponds to frequencies larger than a few MHz. When such a acoustic wave meets the sessile drop, its energy is radiated in the liquid, which leads to complex coupling between acoustics and hydrodynamics. The dissipation of acoustic energy occurring at such high frequency leads to the generation of a streaming flow. Furthermore, if dissipation is weak enough, a significant part of the wave is reflected on the liquid/air interface, which can lead to acoustic radiation pressure of the same order as the capillary pressure. In turn, the free-surface can be highly deformed and show a complex spatio-temporal behavior. In its simplest form, the dynamics shows oscillations of frequency ranging between 20 and 200 Hz, i.e. compatible with the first resonance mode of inertia-capillary regimes. From experiments, we analyze qualitatively this behavior in terms of a self-adaptation of the drop shape via a feedback on the acoustic field. | ||
