How to Achieve a Monostable Cassie State on a Micropillar-Arrayed Superhydrophobic Surface

Area of Science:

• Materials Science
• Surface Science
• Physics

Background:

• Superhydrophobic surfaces with a monostable Cassie state offer diverse applications, including microfluidics, oil-water separation, drag reduction, self-cleaning, and heat dissipation.
• Maintaining a stable monostable Cassie state under external interference remains a significant challenge in superhydrophobic surface design.

Purpose of the Study:

• To theoretically investigate the wetting process of droplets on trapezoidal micropillar-arrayed superhydrophobic surfaces.
• To analyze the Gibbs-free energy and energy barriers to understand wettability transitions.
• To establish a framework for designing superhydrophobic surfaces with tunable wettability.

Main Methods:

• Theoretical analysis of Gibbs-free energy and energy barriers for droplet wetting stages.
• Division of the wetting process into six possible stages.
• Investigation of the influence of micropillar geometry on wettability states.

Main Results:

• The final stable wettability (Wenzel, metastable Cassie, or monostable Cassie state) is determined by the apparent contact angle of the micropillar's lateral surface.
• The geometry of microstructures explicitly controls the size of wettability regions.
• The model is validated by existing experimental data and numerical simulations.

Conclusions:

• The study provides a theoretical basis for classifying wettability on trapezoidal micropillar-arrayed superhydrophobic surfaces.
• Precise tuning of microstructure geometry allows for the design of surfaces with desired wettability.
• The findings are applicable to various functional surfaces and can be extended to triangular and rectangular micropillar designs.