Wetting transition energy curves for a droplet on a square-post patterned surface

Area of Science:

• Surface Science
• Materials Science
• Green Technologies

Background:

• Biomimetic superhydrophobic surfaces offer water repellence, driving applications in green technologies.
• Wetting transitions between Cassie-Baxter and Wenzel states are critical for stable superhydrophobic surfaces but remain poorly understood.
• Existing theoretical, experimental, and numerical studies have not fully elucidated the underlying mechanisms.

Purpose of the Study:

• To investigate the mechanism of wetting transitions between Cassie-Baxter and Wenzel states.
• To analyze the free energy curves associated with these transitions.
• To understand the factors contributing to the irreversibility of wetting transitions.

Main Methods:

• Theoretical analysis of free energy curves for wetting transition processes.
• Inclusion and analysis of gravity effects on energy barriers.
• Numerical simulations using a phase field lattice Boltzmann method with a large density ratio.

Main Results:

• Free energy curves reveal the existence of energy barriers for wetting transitions, with or without gravity.
• Different transition routes for Cassie-to-Wenzel and Wenzel-to-Cassie transitions explain the observed irreversibility.
• Numerical simulation results demonstrate good agreement with theoretical predictions.

Conclusions:

• The study provides a detailed understanding of the free energy landscape governing wetting transitions.
• Irreversibility in wetting is attributed to distinct pathways for forward and reverse transitions.
• The findings are crucial for designing and fabricating stable superhydrophobic surfaces for technological applications.