Superhydrophobic (SH) surfaces are super water repellent surfaces on which a droplet of water will bead up like a marble and roll off the surface with minimal tilting of the surface. This is caused by the combination of a hydrophobic coating and a rough surface structure. To achieve thermodynamic stability, surface tension of the water pulls the droplet into this shape to minimize the contact area between the droplet and the surface. This creates a high contact angle (CA) between the droplet and the surface and a low sliding angle (SA) of which the droplet begins to roll off the surface. SH surfaces have a variety of potential applications such as drag reduction, anti-icing, improved heat transfer through condensation, and self-cleaning. Numerous reports have been dedicated to exploring the fluid dynamic behavior of water droplets on SH surfaces. This thesis focuses on exploring the self-cleaning properties of SH surfaces. Surfaces contaminated with salt, tobacco, and pollen are cleaned by rolling water droplets over the surface or condensing water on the surface such that when large enough, these droplets roll away due to gravity. SH surfaces explored here are composed of micro-scale or nano-scale rib and cavity structures and are compared with smooth, hydrophobic surfaces with a similar hydrophobic coating. To determine the self-cleaning efficiency of each surface, the CA and SA were measured before and after each surface was cleaned. In this study, it was observed that the presence of each of the three contaminates considered greatly affects the overall hydrophobicity of the surface, as indicated by the CA and SA. Ideally, as the contaminates are removed from the surface, the hydrophobicity of the surface improves to match the hydrophobicity of a clean surface. This is best seen on surfaces contaminated with salt as the CA and SA match that of a clean surface after only two to three water droplets roll over the surface or after the first condensed water droplets roll off the surface. This implies that all the salt particles are removed from the SH surface. Surfaces contaminated with tobacco showed that the hydrophobicity improves to a limited extent when cleaned with rolling water droplets or condensation but never is capable of matching the hydrophobicity of a clean surface. This suggests that only a portion of the tobacco residue is capable of being removed from the surface by either of the two cleaning methods considered in this thesis. Finally, when water came in contact with pollen on the surfaces, it experienced hydrodynamic osmosis leading to cellular bursting. After cellular bursting, the surface behaves as a hydrophilic surface and selfcleaning properties were never observed on any surface contaminated with pollen. Thus, overall this study shows that rolling water droplets over a contaminated surface and condensing water droplets on a contaminated surface are both viable means of utilizing the self-cleaning properties on SH surfaces. For the contaminates considered in this study, the efficiency of the self-cleaning surfaces is shown to be the same for both micro-structured and nano-structured surfaces.
College and Department
Ira A. Fulton College of Engineering and Technology; Mechanical Engineering
BYU ScholarsArchive Citation
Miller, David Leland, "A Comparison Between Self-Cleaning Properties via Rolling Droplets and Condensation on Superhyrophobic Surfaces" (2017). All Theses and Dissertations. 6594.
Superhydorphobic, Self-Cleaning, Lotus Effect, Condensation