Drag reduction on laser-patterned hierarchical superhydrophobic surfaces.

Area of Science:

• Surface science and fluid dynamics.
• Micro/nano-fabrication technologies.

Background:

• Drag reduction is crucial for improving energy efficiency in fluid systems.
• Achieving stable hydrophobic surfaces that minimize liquid friction remains a challenge.
• Hierarchical surface structures offer potential for enhanced drag reduction.

Purpose of the Study:

• To investigate the drag reduction capabilities of hierarchical laser-patterned surfaces.
• To correlate surface topography and chemistry with slip length and drag reduction.
• To compare different surface arrangements for optimal performance.

Main Methods:

• Fabrication of hierarchical micro/nano-structured copper surfaces using multi-pass laser scanning.
• Characterization of surface topography and wetting states (Cassie wetting).
• Measurement of slip length using a rheometer setup under liquid flow conditions.

Main Results:

• A significant increase in slip length (up to 111%) was observed on hierarchical surfaces compared to non-hierarchical ones.
• Secondary roughness levels on the patterned surfaces were identified as key to increased slip length.
• Different lattice arrangements (square, hexagonal, grates) showed varying drag reduction efficiencies.
• Silanization of surfaces further enhanced slip length, explained by altered liquid-vapor interface penetration.

Conclusions:

• Hierarchical laser-patterned surfaces effectively reduce drag by promoting stable Cassie wetting.
• Surface topography, specifically secondary roughness, and chemistry play critical roles in drag reduction.
• Optimized hierarchical structures and surface treatments offer a promising avenue for fluid drag reduction technologies.