Collaborative Research: Electrorotational fluid instabilities

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A particle can spontaneously start spinning in an electric field, a phenomenon called Quincke rotation. This project will explore fundamentals and applications of electrorotation in fluid systems such as liquid droplets. The fluid-fluid interface can flow and the drop can deform, which creates a plethora of unexplained flow behaviors: a drop can tumble or beat like a heart, or small particles attached to the drop surface can cluster into vortices. The project will experimentally map electrorotational flows as a function of fluid properties and field strength. The experimental results will be used to develop models to elucidate the observed instabilities. In addition to advancing basic knowledge, the research will provide insights on how to harness these novel electrorotational flows for engineering of complex flows or of novel colloidal products such as patchy particles with dynamic surface patterns. At UCSD, the PI has been involved in engineering outreach to local high-school students, in the form of a summer course entitled "Introduction to Fluid Mechanics in Engineering: From a Straw to an Airplane." The results from this research can be folded into materials to support outreach of students"The electrohydrodynamic flow about a leaky-dielectric liquid drop can undergo intriguing instabilities which involve generation of rotational flow, e.g., drop steady tilt or tumbling, or of vortices as previously observed on the surface of particle-coated drops. This project will establish the mechanisms of these electorotational fluid instabilities by developing (i) numerical simulations, based on the three-dimensional Boundary Integral Method, and (ii) analytical models using asymptotic methods, of drop dynamics in electric fields. Experiments will be designed and carried out to guide and validate the computations and analytical results. The driving hypothesis is that electrorotational fluid instabilities are related to the Quincke effect (the spontaneous rotation of a particle in a uniform DC electric field occurring above a threshold field strength). The research outcomes will lead to a much deeper understanding of the underlying physics as well as the discovery of new dynamical regimes and engineering opportunities. The potentially transformative nature of the proposal lies in the unexplained emergent behavior of the system that could inspire new research directions and applications related to complex fluids, instabilities and interfacial flows.