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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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Direct force measurement of microscopic droplets pulled along soft surfaces
Hamza K Khattak1, Stefan Karpitschka2, Jacco H Snoeijer3
1Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4M1, Canada.
Nature Communications
|July 30, 2022
Summary
Energy dissipation in microscopic droplets moving on soft surfaces is strongly linked to capillary ridge motion. Increasing substrate stiffness reduces this dissipation, a trend explained by scaling analysis beyond small deformation theory.
Area of Science:
- Physics
- Materials Science
- Fluid Dynamics
Background:
- Surface tension drives deformation of soft substrates by droplets, forming capillary ridges.
- Understanding energy dissipation during droplet motion on soft matter is crucial for microfluidics and soft robotics.
Purpose of the Study:
- To investigate the relationship between capillary ridge motion and energy dissipation in microscopic droplets on soft surfaces.
- To explore how substrate effective stiffness influences this energy dissipation mechanism.
Main Methods:
- Utilized a micropipette-based method for simultaneous imaging and force measurement of moving microscopic droplets.
- Varied the thin film thickness on a rigid substrate to tune the effective stiffness of the soft surface.
- Controlled capillary ridge size by adjusting substrate stiffness without altering surface chemistry.
Main Results:
- Observed that energy dissipation is highly dependent on the film thickness (effective stiffness).
- Found a monotonic decrease in dissipation as the effective stiffness of the substrate increased.
- Demonstrated that this trend extends beyond the predictions of small deformation theory.
Conclusions:
- The study reveals a direct correlation between substrate stiffness and energy dissipation during droplet motion on soft surfaces.
- A simple scaling analysis provides an explanation for the observed monotonic trend, extending theoretical understanding.
- Findings offer insights into controlling energy dissipation in microscale fluid-substrate interactions.
