Satish Kumar (Univ. of Minnesota)

Droplet dynamics near topographical features

While solid substrates are often idealized as being perfectly smooth, all real surfaces possess some level of topographical and chemical heterogeneity. This heterogeneity can greatly influence droplet dynamics, and is of tremendous relevance for applications ranging from oil recovery to water harvesting to advanced manufacturing. In this talk, we will show how mathematical models based on lubrication theory that account for surface topography provide insight into how topographical features induce pinning of the three-phase contact line where the liquid, air, and solid all meet. Sufficiently strong external forces cause contact-line depinning, and in some cases the depinning force can be understood through relatively simple scaling relationships. Three examples will be presented involving (i) shear-induced depinning, (ii) gravity-induced depinning, and (iii) evaporation-induced depinning. Comparisons to existing experimental observations will be discussed.

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Satish Kumar is a Distinguished McKnight University Professor at the University of Minnesota, where he is on the faculty of the Department of Chemical Engineering and Materials Science. Prof. Kumar received his undergraduate degree from Minnesota (1993), and his master's (1994) and doctoral degrees (1998) from Stanford University, all in chemical engineering. Following postdoctoral work at École Normale Supérieure (Paris) and the University of Michigan, he joined the faculty at Minnesota in 2001. Prof. Kumar is a Fellow of the American Physical Society (APS), is Co-Editor-in-Chief of the Journal of Engineering Mathematics, and serves on the editorial board of the Journal of Non-Newtonian Fluid Mechanics. He has been recognized for outstanding reviewing by the APS and the Journal of Fluid Mechanics, and received the 2025 William R. Schowalter Lectureship from the American Institute of Chemical Engineers. Prof. Kumar currently serves as Vice-Chair of the APS Division of Fluid Dynamics, and as a member of the U. S. National Committee on Theoretical and Applied Mechanics. He is also a former president of the International Society of Coating Science and Technology. For 7 years, Prof. Kumar served as Faculty Director of the Industrial Partnership for Research in Interfacial and Materials Engineering (IPRIME), a university-industry consortium, and is currently director of its Coating Process Fundamentals Program. Prof. Kumar's research involves integration of transport phenomena, colloid and interface science, rheology, applied and computational mathematics, and experiments to address fundamental issues motivated by problems in materials processing. These fundamental investigations, which are described in 174 journal articles and 31 PhD theses, are frequently inspired by industrial applications such as coating and printing processes, polymer processing, nanofluidics/microfluidics, and energy.