Wetting on Micropatterned Surfaces: Partial Penetration in the Cassie State and Wenzel Deviation Theoretically...

Area of Science:

• Surface science
• Fluid dynamics
• Materials science

Background:

• Liquid droplets on micropatterned surfaces can adopt Cassie-Baxter (Cassie) or Wenzel states.
• Understanding these wetting states is crucial for designing advanced materials.

Purpose of the Study:

• Investigate wetting phenomena on ideal, straight micropillared surfaces.
• Analyze droplet behavior and energy states using thermodynamic and CFD models.
• Explain deviations from the Wenzel equation prediction.

Main Methods:

• Thermodynamic modeling of the droplet-solid-gas system, including novel sagging, touchdown, and liquid-volume submodels.
• Computational fluid dynamics (CFD) simulation of 3D dynamic wetting.
• Validation of thermodynamic results using CFD.

Main Results:

• Identified a small energy barrier between Cassie and Wenzel states.
• Observed no partial penetration or sagging in the Cassie state on ideal surfaces.
• Demonstrated a Wenzel state apparent contact angle up to 5° lower than Wenzel equation predictions for pillars ≥ 75 μm.

Conclusions:

• The study provides the first theoretical explanation for Wenzel deviation on micropatterned surfaces.
• Thermodynamic and CFD models confirm findings on wetting behavior and energy barriers.
• Results offer new insights into droplet behavior on engineered surfaces.