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Updated: Aug 9, 2025
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Measuring the Interaction Force Between a Droplet and a Super-hydrophobic Substrate by the Optical Lever Method
Published on: June 14, 2019
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Energy Loss for Droplets Bouncing Off Superhydrophobic Surfaces
Calvin Thenarianto1, Xue Qi Koh1, Marcus Lin2
1Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore 138634.
Langmuir : the ACS Journal of Surfaces and Colloids
|February 16, 2023
Summary
Water droplet rebound energy loss on superhydrophobic surfaces depends on impact speed. At low speeds, surface wetting dominates; at high speeds, inertial-capillary effects prevail, offering a new understanding of droplet dynamics.
Area of Science:
- Fluid Dynamics
- Surface Science
- Materials Science
Background:
- Water droplets rebound multiple times from superhydrophobic surfaces.
- Quantifying energy loss via the restitution coefficient (e = rebound speed/impact speed) is crucial.
- A mechanistic explanation for energy loss during droplet rebounds remains elusive.
Purpose of the Study:
- To investigate the energy loss mechanisms of rebounding water droplets.
- To determine the restitution coefficient (e) across a range of impact speeds.
- To elucidate the influence of surface properties on droplet rebound dynamics.
Main Methods:
- Experimental measurement of the restitution coefficient (e) for submillimeter and millimeter water droplets.
- Impact tests conducted on two distinct superhydrophobic surfaces.
- Analysis of rebound behavior over a wide range of initial impact speeds (4-700 cm s^-1).
Main Results:
- Observed a nonmonotonic dependence of the restitution coefficient (e) on the initial impact speed (U_I).
- At low U_I, energy loss is governed by contact-line pinning and sensitive to surface wetting properties like contact angle hysteresis (Δ cos θ).
- At high U_I, energy loss is dominated by inertial-capillary effects and independent of Δ cos θ.
Conclusions:
- Proposed simple scaling laws to explain the observed nonmonotonic behavior of the restitution coefficient.
- Differentiated energy loss mechanisms based on impact speed regimes.
- Highlighted the critical role of surface wetting properties at low impact speeds and inertial-capillary effects at high impact speeds for droplet rebounds.
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