Hydrodynamic Drag Force Measurement of a Functionalized Surface Exhibiting Superhydrophobic Properties

Comparing the skin friction drag effects of a superhydrophobic flat plate to an untreated flat plate of the same material and geometry.

Naval Postgraduate School, Monterey, California

With superhydrophobic properties being extended to a variety of metallic substrates through the process of ablation due to femto-second laser surface processing (FLSP), it is important to understand the hydrodynamic benefits of such a material, as well as its resiliency. This research focuses on the skin friction drag effects of a superhydrophobic flat plate compared to an untreated flat plate of the same material and geometry. The resiliency of this material will also be tested through the use of an accelerated corrosion fog chamber using both treated and untreated aluminum samples.

A material is said to be superhydrophobic if the equilibrium contact angle of a water droplet is greater than 150 degrees and the contact hysteresis angle is less than 10 degrees. The idea of extending superhydrophobic properties to a range of materials was first inspired by observing the water repelling and self-cleaning effects of the lotus leaf and a number of other leaves found in nature. Due to the large contact angle, the water droplets center of mass is moved further above the surface causing the droplets to have a rolling action rather than a sliding action. This, combined with the more uniform surface tension of spherical geometry, allows particles to become trapped in the droplet and carried away as seen in Figure 1.