Super liquid-repellent layers: The smaller the better.

Area of Science:

• Surface science
• Materials science
• Fluid dynamics

Background:

• Super liquid-repellent surfaces require high impalement pressure and contact angles.
• Achieving high apparent receding contact angles is crucial for robust liquid repellency.

Purpose of the Study:

• To theoretically analyze models for super liquid-repellent layers.
• To determine the optimal feature size for maximizing impalement pressure and apparent receding contact angle.

Main Methods:

• Theoretical analysis of two models: superhydrophobic cylindrical micropillars and superamphiphobic pillars of spheres.
• Derivation of an expression for apparent receding contact angle based on force balance.
• Experimental validation using confocal microscopy of water droplets on hydrophobic pillars.

Main Results:

• The ratio of pillar width to spacing (w/a) is a key factor in controlling the receding angle.
• Minimizing the absolute size of surface features, while keeping w/a constant, maximizes impalement pressure.
• Smaller features lead to enhanced super liquid-repellent properties.

Conclusions:

• Feature size is a critical parameter for designing effective super liquid-repellent surfaces.
• The study provides a design principle for optimizing surface structures to achieve superior liquid repellency.
• Minimizing feature dimensions is essential for maximizing impalement pressure and apparent receding contact angle.