CAREER: Tuning liquid jet and splash dynamics by deformable and heterogeneous boundaries

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The stability of liquids flowing through gas is relevant to drug delivery, fabrication processes, and thermal management. The stability depends on the properties of the flowing fluid and on the mechanical and surface properties of the solid bodies in the system. To better understand the stability of liquid flow in these systems, this project will study how the properties of solid bodies affect both free liquid jets and water entry splashes. Specifically, this research will introduce (i) soft materials that deform in response to fluid motion, and (ii) spatially nonuniform solid wetting properties where the air, liquid, and solid phases meet. The feature of greatest interest in jets is the length at which the coherent liquid column disintegrates into drops. Here, this length will be controlled by employing deformable nozzles and nonuniform surface chemistry (i.e. wetting properties) at the orifice. In studying water entry, a solid impactor splashes into a liquid pool, and the resulting dispersed liquid and air-entraining cavity behavior are of interest. Such splash features will be modified using both solid projectiles with chemically nonuniform surfaces and via compliant solid films atop the liquid surface. These scientific endeavors integrate educational activities that engage local high school students and educators in the scientific process through lectures, classroom flow control experiments, mentored science fair projects, and research engagement workshops for teachers.The characterization of the coupled physics of dynamic three-phase contact lines with soft solids is in its infancy. This research effort seeks to explore fluid flows where the multiphase interface has been modified via material compliance and surface treatments. Experiments and theory will be used to understand the physics of jet stability with the inclusion of the aforementioned passive flow modifiers. A new understanding of initial disturbances and their suppression within free stream liquid jets will inform the adaptation of linear jet stability theory for deformable nozzles. The modification of free liquid surfaces with compliant media and the alteration of solid projectiles with heterogeneous boundaries will produce new theoretical treatments at moderate Weber numbers for vehicles entering water. Thus, conditions for cavity creation and collapse will be redefined, and the limits of lift force production from non-axisymmetric cavities will be explored. Experimental techniques include high-speed videography to capture flow features, digital tracking to elucidate kinematics, microscopy to image surfaces, and X-ray photoelectron spectroscopy to chemically characterize the solid surfaces used in this study.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.