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Unraveling friction forces of droplets on a non-wetting surface

Abhijit Kumar Kushwaha1,*, Sankara Arunachalam1, Ville Jokinen2, Dan Daniel1,3, and Tadd T. Truscott1,†

  • 1Mechanical Engineering, Physical Science and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
  • 2Department of Chemistry and Materials Science, School of Chemical Engineering, Aalto University, Espoo 02150, Finland
  • 3Droplet and Soft Matter Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa 904-0495, Japan

  • *Contact author: akushwaha.iitk@gmail.com
  • †Contact author: taddtruscott@gmail.com
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Phys. Rev. Fluids 10, 103603 – Published 22 October, 2025

DOI: https://doi.org/10.1103/y86v-8rgs

Abstract

Understanding the friction forces acting on droplets moving across non-wetting surfaces is essential for advancing applications in fluid transport and microfluidics. In this study we quantify droplet friction on both superhydrophobic and superheated (Leidenfrost) substrates using two complementary experimental approaches: inclined plane dynamics and cantilever force sensing. We identify distinct friction regimes governed by contact-line pinning, viscous dissipation, and aerodynamic drag over a broad range of velocities and viscosities. A force-based scaling law captures the transition between these regimes as a function of the capillary number, integrating contact-line effects, internal dissipation, and aerodynamic contributions. Our model is further validated through white light interferometry and high-speed reflective interference contrast microscopy, which reveal the structure and evolution of the thin air or vapor layers beneath the droplets. These findings offer a comprehensive framework for predicting droplet behavior on non-wetting surfaces and inform the design of surfaces for reduced friction in engineering and microfluidic systems.

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Outline

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Phys. Rev. Fluids 10, 103603– Published 22 October, 2025
  • Received 30 May 2024
  • Accepted 22 September 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by King Abdullah University of Science and Technology (KAUST).

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