Date of Award

9-4-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Applied Science

First Advisor

Tansel Karabacak

Abstract

In this work, superamphiphobic (SAP, i.e. super-repellent toward water and oils) metallic aluminum alloy 2024 surfaces were produced with water and oil contact angles of more than 150° and sliding angles of less than 10°. The two simple and environmentally friendly techniques of mechanical sanding and boiling water treatment were used to introduce micro- and nano-scale roughnesses, respectively, which resulted in a hierarchical morphology. Surface energy of the rough surfaces was reduced by coating them with 1H, 1H, 2H, 2H-Perfluorodecyltriethoxysilane (PFDTS). SAP property was absent for samples with micro- or nano-roughness only, and it emerged only after both kinds of roughnesses were introduced. The highest contact angles approaching 158° for water, 156° for ethylene glycol and 154° for peanut oil were obtained by one-directional sanding and nanograss. The effects of the two approaches of random and one-directional sanding using various sandpaper grits and different time periods of treatment with boiling de-ionized water on the wettability of surfaces were also investigated. In addition, fundamental wetting models of Wenzel and Cassie-Baxter were used in order to explain the experimental results obtained. Furthermore, in order to investigate the effect of polar groups of long chain fluorocarbon polymers on SAP property of rough Al alloy surfaces and its robustness, three long chain fluorocarbon polymers with different polar groups were utilized. For this purpose, the three types of long chain fluorocarbon polymers of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane (PFDTS), 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane (PFDCS), and perfluorooctanoic acid (PFOA) were chemically vaporized onto flat and hierarchical (micro and nano) rough Al alloy surfaces. The contact angle and sliding angle measurements for water, ethylene glycol, and peanut oil verified the SAP property of hierarchical rough Al alloy surfaces treated with alkylsilane polymers (PFDTS, PFDCS). However, the hierarchical surfaces treated with fluorocarbon polymer with polar acidic end (PFOA) showed highly amphiphobic properties but could not reach the threshold for SAP. Chemical stability of the hierarchical Al alloy surfaces treated with the three long chain fluorocarbon polymers was tested under the harsh conditions of annealing at 200 oC and ultrasonication in acetone as the function of time. In addition of promoting SAP property, the PFDCS polymer exhibited the best chemical stability. Finally, anisotropic textured surfaces of microgroove and hierarchical microgroove/nanograss structures were studied for their potential application in directional wetting. After treatment with PFDCS polymer, the wetting anisotropy of the two rough Al alloy surfaces were investigated by measuring the water and oil droplets' parallel and normal contact angles, contact lines, and sliding angles as well as their anisotropic factors for two different masses of the liquid droplets. Microgroove structures showed an overall greater anisotropy for the liquids with various surface tensions. However, hierarchical (microgrooves + nanograss) structures showed significant anisotropy only for low surface tension oils. This distinct behavior of hierarchical surfaces obtained in this study could be useful for self-cleaning and separation of water and oil.

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