Bouncing droplets: from fundamentals to digital microfluidics

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0966452BushA series of experiments will explore novel bouncing configurations of small liquid droplets that may bounce indefinitely on a vertically vibrated liquid interface. Accompanying theoretical models will be developed. In certain forcing regimes, these bouncing droplets walk steadily across the interface; moreover, these bouncers or walkers can interact in a variety of ways, repelling or attracting, forming stable lattice structures that translate or rotate, or merging to produce a larger drop that may coalesce with the underlying bath. This novel means of drop levitation provides an attractive alternative for handling droplets for microfluidic applications, as it avoids the complications resulting from fluid-solid contact. The proposed research will be directed towards better understanding the rich dynamics of bouncing droplets with a view to informing and developing new digital microfluidic technologies. Intellectual Merit: The work builds on the observations of Yves Couder and coworkers who have demonstrated that the bouncing droplet experiment is extraordinarly rich, exhibiting features of optics (diffraction), quantum systems (wave-particle duality, tunneling), statistical physics (phase transitions) and astronomy (complex orbital motions). Most startling is the fact that millimetric walking droplets exhibit features of quantum systems (e.g. photons) that are smaller by a factor of 10 billion and governed by the probabilistic laws of quantum mechanics. A salient question is whether the diffraction of walkers passing through a slit is an example of chaotic dynamics giving rise to apparent quantum behavior. An improved understanding of the bouncing dynamics will yield valuable insight into the quantum nature of bouncing droplets. The proposed exploratory examination of droplets bouncing on a rotating bath will provide a novel system with features (gravitational attraction, orbital motions and collision) analogous to those arising celestial dynamics. The release of multiple walkers onto a rotating bath will thus represent a simple and provocative laboratory analogue of planetary accretion and solar system evolution.Broader Impact: Droplets bouncing on a vibrated interface is a visually striking effect that may be reproduced with a simple desktop experiment. Moreover, walking droplets exhibit features of wave-particle duality, and so represent a provocative macroscopic analogue of a quantum mechanical system. As such, bouncing droplets are ideally suited to attract the interest of both science students and the general public. The PI's work on the subject has received considerable media attention. Such exposure should increase the general public's awareness and appreciation of science, and attract the attention of science museums. The research will be performed in part by undergraduate students supervised by the PI and co-PI. The experiments are particularly straightforward, and so provide an ideal entry into the lab environment for MIT undergraduates. The PI's laboratory has a long history of undergraduate involvement through MIT's UROP Program, with women and underrepresented minorities being hired preferentially. The PI is actively involved in both high school outreach and MIT's Science and Engineering Program for Teachers.