Drop Friction and Failure on Superhydrophobic and Slippery Surfaces.

Area of Science:

• Surface science
• Materials science
• Fluid dynamics

Background:

• Droplet mobility on surfaces impacts cleaning efficiency, fogging, icing, and fouling.
• Both superhydrophobic and liquid-infused surfaces exhibit high droplet mobility.
• These surfaces utilize different lubrication mechanisms: trapped air pockets for superhydrophobic and immiscible liquid lubricants for infused surfaces.

Purpose of the Study:

• To review criteria for stable wetting states with low friction and high droplet mobility on superhydrophobic and liquid-infused surfaces.
• To discuss proposed mechanisms explaining friction origins on these surfaces.
• To highlight the distinct differences in droplet behavior and collapse mechanisms between the two surface types.

Main Methods:

• Review of experimental and computational methods.
• Analysis of static and dynamic wetting properties.
• Comparison of Cassie-to-Wenzel state transition pathways.

Main Results:

• Superhydrophobic and liquid-infused surfaces achieve high droplet mobility through different lubrication strategies.
• Droplets can transition from a low-friction Cassie state to a high-friction Wenzel state on both surface types.
• Liquid-infused surfaces exhibit a distinct 'wetting ridge' that influences droplet shape, friction, and collapse mechanisms, unlike superhydrophobic surfaces.

Conclusions:

• Liquid-infused surfaces are not merely superhydrophobic surfaces with liquid lubricant replacing air pockets.
• The wetting ridge on liquid-infused surfaces fundamentally alters droplet properties and collapse dynamics.
• Understanding these differences is crucial for designing advanced surfaces for various applications.