Generalized model for static contact angles and hysteresis on micro/nanostructured surfaces.

Area of Science:

• Surface Science
• Materials Science
• Fluid Dynamics

Background:

• Understanding surface wetting is crucial for applications like microfluidics and coatings.
• Existing models often simplify surface topography and liquid interactions.
• Real-world conditions introduce complexities like contamination and environmental fluctuations.

Purpose of the Study:

• To develop a general model for predicting static contact angles and contact angle hysteresis.
• To account for arbitrary fractions of air entrapment and liquid infiltration in surface topography.
• To provide guidance for designing surfaces with tunable wetting properties.

Main Methods:

• A compact, general model was developed.
• The model incorporates local surface topography (random or periodic).
• It considers localized air entrapment and liquid infiltration at the contact line.

Main Results:

• The model recovers classical wetting limits (Wenzel, Cassie-Baxter, hemiwicking).
• It accounts for intermediate wetting states, including impregnating Cassie.
• A novel 'inverse Wenzel state' (bulk Cassie with ambient liquid film) was identified.

Conclusions:

• The model offers actionable guidance for designing micro/nanostructured surfaces.
• It enables modulation of contact angle hysteresis under unpredictable conditions.
• Predictions are relevant for real-world applications facing fouling, aging, and environmental variations.