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Kirill Misiiuk1,2,3, Andrew Sommers4, Geoff R Willmott2,5
1Department of Physics, University of Otago, 730 Cumberland Street, Dunedin, Otago 9016, New Zealand.
Droplets can move directionally on surfaces without wettability gradients due to geometric asymmetry. This study shows water droplets move inward on microstructured rings, driven by radial curvature effects.
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Area of Science:
- Fluid dynamics
- Surface science
- Microfluidics
Background:
- Directional droplet motion is typically linked to surface wettability gradients.
- Geometric asymmetry on microstructured surfaces can also induce droplet motion.
- Understanding these non-gradient driven motions is crucial for microfluidic applications.
Purpose of the Study:
- To investigate directional droplet motion on microstructured surfaces lacking wettability gradients.
- To elucidate the role of geometric asymmetry in droplet transport.
- To explore new methods for fluid management in microscale systems.
Main Methods:
- High-speed imaging to capture droplet dynamics post-impact.
- Goniometric analysis to assess wetting properties.
- Modeling of droplet contact area to analyze geometric asymmetry.
Main Results:
- Water droplets (2.6 mm) impacted concentric rings (25 and 100 μm pitch) and exhibited net inward motion.
- This motion occurred despite the absence of chemical or topographic gradients.
- Fabrication variations led to nonuniform wetting, and geometric asymmetry in curvature influenced wetting interactions.
Conclusions:
- Geometric asymmetry and radial curvature can induce directional droplet motion on non-gradient surfaces.
- These factors create 'gradient-like' behavior without actual gradients.
- Findings offer new insights for fluid management and microfluidic system design.