Superhydrophobic Properties of Replicated Laser Microtextured Surfaces

Caffrey, Paul, Electrical Engineering - School of Engineering and Applied Science, University of Virginia
Gupta, Mool, Department of Electrical and Computer Engineering, University of Virginia

The fields of anti-icing technology, aviation, solar energy, wind energy, various corrosion susceptible systems and EMI shielding etc. would greatly benefit with the development of superhydrophobic surfaces and materials. Consequently, the synthesis, fabrication and characterization of superhydrophobic coatings and materials have seen rapid expansion recently. It is difficult to obtain a water contact angle greater than 150° and a sliding angle of less than 10° (superhydrophobic surfaces) through surface treatments, by the application of environmentally stable chemical coatings or by choice of materials. However, the combination of hydrophobic material properties with surface roughness at micro/nano scale could provide very high water contact angles typically greater than 160 degrees.

In this dissertation a laser processing method is investigated to generate a microtextured surface that is then replicated on a polymer surface (PDMS). This replicated microtextured surface is then characterized for its optical and superhydrophobic properties. No additional coatings on the polymer are necessary to deliver contact angles greater than 161°. Multiwall Carbon nanotubes are then added to the polymer matrix to produce an electrically conductive nanomaterial with microtexture surface roughness and this resulting conductive nanocomposite is characterized for its superhydrophobic properties and its electrical resistivity. The electrical conductivity was controlled by changing the amount of MWCNT that is added to the polymer matrix. A conductivity improvement over pure PDMS of more than 1011 is found with a resistivity of ρ = 761 Ω cm. Both the microtextured PDMS and conducting nanocomposite were investigated for electrowetting control of contact angle and it was discovered that reversible electrowetting can be demonstrated in the Cassie-Baxter region of more than ten degrees with no additional oil or other surface treatments. These replicated microtextured polymer surfaces have great potential for various commercial applications that require water repellency for anti-icing, corrosion protection and others.

PHD (Doctor of Philosophy)
Superhydrophobic, Electrowetting, Microtexture, Conductive nanocomposite, Contact angle
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