Extremely stable underwater superhydrophobicity via plasma micro-nanotexturing

Area of Science:

• Materials Science
• Surface Chemistry
• Fluid Dynamics

Background:

• Inspired by the Salvinia molesta leaf, underwater superhydrophobic surfaces utilize a stable air layer (plastron) to prevent wetting.
• External forces like hydrostatic pressure and water flow typically destabilize this plastron, limiting real-world applications.

Purpose of the Study:

• To test the hypothesis that textured superhydrophobic surfaces can achieve long-term plastron stability under challenging underwater conditions.
• To develop and characterize Poly(methyl methacrylate) (PMMA) surfaces with hierarchical micro-nanotextures for enhanced underwater performance.

Main Methods:

• Fabrication of hierarchically structured superhydrophobic PMMA surfaces using plasma nanotechnology.
• Assessment of plastron stability under simulated immersion depths (up to 15 m) and continuous water flow (up to 350 ml·min⁻¹).
• In situ monitoring of plastron thickness and air layer dynamics using White Light Reflectance Spectroscopy (WLRS) in air-undersaturated water.

Main Results:

• The fabricated PMMA surfaces demonstrated durable superhydrophobicity and stable plastrons under high overpressures and continuous water flow.
• A stable plastron was maintained for at least two weeks under a pressure equivalent to a 10-m water depth.
• The surfaces showed resilience even in air-undersaturated water, a more demanding condition than typical seawater immersion.

Conclusions:

• Appropriately textured superhydrophobic surfaces can provide robust, long-term plastron stability in challenging underwater environments.
• The study provides insights into plastron lifetime mechanisms and strategies for achieving durable underwater superhydrophobicity.
• These findings pave the way for advanced anti-fouling and drag-reduction technologies in marine applications.