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Full Name:Muhammad Rizwan Yousaf

Thesis Title:Development of Transparent Superhydrophobic and Self-Cleaning Surfaces

Major Field:Mechanical Engineering (Materials and Manufacturing)

Date of Degree:March 2017



Wetting characteristics of surfaces are influenced by both, the surface texture and the surface energy of substrate materials. Surfaces consisting of a hierarchal texture covered with a low surface energy material show unusual water repellency and are termed as superhydrophobic surfaces. A water droplet on such surface rolls off at small inclination angles, and picks and carries away small particles along its path, thereby, giving rise to the self-cleaning effect. These surfaces have attracted considerable attention in recent years due to their vast technological applications ranging from self-cleaning windows, textiles, and paints to low drag surfaces for energy conversion.

Replication of textured surfaces by PDMS (Polydimethylsiloxane) is introduced as a fast and cost effective way of making optically transparent superhydrophobic surfaces. Laser textured alumina tiles and photo lithographically etched silicon wafers are used as templates for replication studies. Surfaces obtained by replicating laser textured alumina tiles exhibit smaller water contact angles (less than 150°) due to the absence of nano-sized whisker like structures. Functionalized silica nanoparticles are, therefore, introduced at the replicated PDMS surfaces to make them superhydrophobic (water contact angle ≥150°). Surfaces obtained by replicating etched silicon wafers, on the other hand, are superior in terms of superhydrophobic characteristics and optical transmittance.

A facile approach to render conventional glass surfaces superhydrophobic is through silica nanoparticle coating. Functionalized silica nanoparticles are synthesized and deposited onto the glass workpieces. The surfaces, thus obtained, give water contact angles exceeding 170° with an average optical transmittance of 67.22%. Improvement in optical transmittance is brought about by using the process of convective assembly to get a thin layer of silica nanoparticles at the glass surface.

Impregnating the texture of a superhydrophobic surface by some lubricant oil is a relatively new concept that is used to impart some beneficial properties to superhydrophobic surfaces. The criterion governing the formation of a stable lubricant oil film on a textured surface is highlighted and oil impregnated surfaces are prepared in accordance with the oil film stability criterion. The last part of the thesis focuses on the characterization of dust particles, collected from Dhahran area, via using advanced analysis techniques.