Wetting of lyophobic textured surfaces and porous materials

Venue: Ferrari Building 1 (Povo) - Room A2014
Time: 2.30pm

Speaker: 

• Dr. Simone Meloni - University of Rome "La Sapienza"

Abstract:

The wetting of lyophobic textured surfaces has a great importance in nature and for technological applications. For example, the air bubbles trapped in the hairs covering the legs of water skaters (Gerridae) allow the insect to float over water; the air layer retained by the surface corrugations of the Lotus leaves ease the rolling of water droplets over them, which helps keeping the plant clean. In general, a liquid deposited on hydrophobic textured surfaces can stay suspended over the corrugations (Cassie-Baxter state), hence reducing the solid/liquid contact area. Thus, the presence of surface corrugations enhances the chemical hydrophobicity of the material (superhydrophobicity). Indeed, these surface corrugations are at the basis of the phenomena just illustrated. There are many (potential) technologies associated to superhydrophobic surfaces; an incomplete list includes drag reduction in maritime transports for an improved energy efficiency; self-cleaning glasses, sanitary fittings and wall paints; anti-moisturing, anti-icing and anti-fogging coatings; surfaces for drop-wise condensation to enhance energy recovery/scavenging and water harvesting; anti-adhesion and anti-corrosion; boiling enhanced heat transfer and many more.
Textured hydrophobic surfaces support a second state, known as the Wenzel state, in which the liquid completely wets the textures. In this state, the properties described above are lost. This fostered an intense experimental and theoretical research on the relative stability of the Cassie-Baxter and Wenzel states, and on the wetting (Cassie-Baxter Þ Wenzel) and recovery (Wenzel Þ Cassie-Baxter) transitions. Addressing these questions might allow to understand why nature has selected the complex surface chemistries and morphologies observed in the skins of insects and spiders and leaves of plants, or to learn novel design principles to optimize artificial surfaces.
In this seminar I will discuss the wetting and recovery transitions at prototypical hydrophobic textured surfaces, illustrating recent advances in confined nucleation theories. I will also touch upon the related problem of intrusion/extrusion in/out of porous lyophobic materials, which are important for energy storage and energy dissipation.