Interaction of multiphase fluids and solids at the microscale

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Multiphase flows are important in a wide variety of processes in science, engineering and medicine. In most cases of practical interest, multiphase flows interact mechanically with deformable solids. Fluid-solid interactions have been widely studied for macroscale problems, where the effect of surface tension is negligible. However, due to the continuous miniaturization of manufactured objects and the importance of surface tension in natural phenomena, there is a critical need to better understand fluid-solid interactions where surface tension plays a predominant role. Using a unique and enabling computational method, this project will unravel the fundamental mechanisms of fluid-solid interactions that couple flow, nonlinear elasticity and surface tension. The proposed research will shed light on the process of spontaneous droplet motion on soft substrates, interfacial instabilities in soft capillary tubes, and pool boiling on deformable solid surfaces. The understanding of these phenomena may bring major advances in bioinspired droplet motion, microfluidics and multiphase heat transfer. The research will be integrated in the curriculum through an initiative to introduce simple concepts of fluid-structure interaction in undergraduate mechanical engineering courses. The project will also offer undergraduate summer research experiences and mentoring activities. The goal of this project is to understand fluid-solid interactions where surface tension interacts with flow, fluid-fluid phase transformations and elastic forces. These phenomena, ubiquitous in microfluidics, medicine, and natural phenomena, have not been previously studied partially due to our lack of theoretical and computational tools. This knowledge gap is limiting our progress on multiphase heat transfer, microfluidics, biofluids and microfabrication, among other science and engineering applications. The current project will leverage a unique computational approach to unveil the fundamental mechanisms controlling this fascinating coupled problem. The project will focus on fundamental scientific problems involving (i) the displacement of a fluid by another fluid in a soft capillary tube, (ii) the spontaneous motion of droplets on soft substrates, and (iii) the effect of deformable substrates on temperature-driven liquid-vapor phase transformations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.