SCHOOL OF MECHANICAL ENGINEERING SEMINAR Monday, August 6, 2012 at 15:00 Wolfson Building of Mechanical Engineering, Room 206

College of Engineering & Applied Science, University of Wisconsin-Milwaukee

Forces that act between the rough or smooth solid surface and a water droplet are remarkably complex and involve various molecular interactions such as adhesive attractive forces (van der Waals, polar, etc) and generalized forces acting on the entire system to minimize its energy and maximize entropy. The situation is even more complex when liquid freezes and ice adhesion is involved. We attempt to separate these forces by considering various systems (air bubble, water droplet, oil droplet in water and in air) and investigating the contact angle (CA) and CA hysteresis. In a solid-water-air system, CA hysteresis characterizes energy dissipation during the flow of a water droplet on a solid surface. Hysteresis exists due to the surface roughness and chemical heterogeneity. It is caused by adhesion hysteresis in the solid-water contact area (2D effect) and by pinning of the solid-water-air triple line (1D effect). In this work it is shown that CA hysteresis is present also in more complex systems, such as an organic liquid (oil) in contact with a solid metallic surface immersed in water. In order to decouple the 1D and 2D effects, we study CA hysteresis in solid-water-air (droplet), solid-air-water (bubble), solid-water-oil and solid-water-air-oil systems. The comparative analysis of these systems allows decoupling the 1D and 2D effects as well as hydrogen bonding and entropic forces (water-air tension) and dispersion forces (oil-air tension). In is further shown that two wetting states (Cassie and Wenzel) can exist in underwater oleophobic metallic surfaces. Application of superhydrophobicity to anti-icing will also be discussed.

Biomimetic superhydrophobic materials for antifouling and anti-icing

Prof. Michael Nosonovsky