Wetting transition on patterned surfaces: transition states and energy barriers

Area of Science:

• Surface science
• Fluid dynamics
• Materials science

Background:

• Understanding wetting transitions on microstructured surfaces is crucial for applications in microfluidics and material design.
• The Cassie-Baxter and Wenzel states describe different liquid behaviors on hydrophobic surfaces.

Purpose of the Study:

• To investigate the wetting transition from the Cassie-Baxter to the Wenzel state on microstructured hydrophobic surfaces.
• To compute transition states, energy barriers, and minimum energy paths for this wetting transition.
• To analyze the influence of surface microstructure and drop size on the wetting process.

Main Methods:

• Utilized the string method to accurately calculate transition states and energy barriers.
• Performed numerical simulations for liquid wetting on a hydrophobic surface with a square pillar lattice.
• Analyzed the liquid front propagation and identified key mechanisms like stepwise infiltration and zipping.

Main Results:

• The wetting transition occurs through a sequence of metastable states, mirroring the surface's microstructure.
• Liquid infiltration initiates in a single groove, followed by lateral spread.
• A zipping mechanism governs infiltration within each layer.
• The energy barrier depends on drop size and pillar spacing.

Conclusions:

• The wetting transition on microstructured surfaces is a complex process involving distinct intermediate states and mechanisms.
• The findings provide insights into controlling liquid behavior on patterned hydrophobic materials.
• This research contributes to the fundamental understanding of fluid-surface interactions in microscale systems.