Superhydrophobicity and Wetting Symposium(MSW-2018), Espoo, Finland, 13 - 18 May 2018, pp.61
The Effect of Surface Geometry and Chemical Composition on Wettability Properties
C. Elif CANSOY1 , Ugur CENGIZ2
1Piri Reis University, Faculty of Science and Letters
2Canakkale Onsekiz Mart University, Faculty of Engineering
Oil and water repellencies of surfaces are crucial properties of materials in many industrial applications such as anti-fouling, oil-water separation, anti-bacterial, anti-icing, anti-fogging, self-cleaning. Wettability of a solid surface can be defined indirectly by liquid contact angle measurements at the three phase boundary of a liquid, solid and vapor intersect. Both surface roughness and chemical heterogeneity affect the wettability of a solid surface. Wenzel and Cassie-Baxter theories were developed to identify the roughness and chemical heterogeneity effect on wettabilities of the surfaces. However, in the recent publications, it was experimentally determined that the applicability of both theories were wrong in case of super liquid repellent surfaces1,2 . Perfluoroalkyl copolymers with varying surface energies3 , polymernano particle composites4 and geometrically patterned2 surfaces can be used to prepare liquid repellent surfaces. When the effect of perfluoroalkyl content and hydrocarbon chain lengths on oleophobic properties of perfluoroethyl alkyl methacrylate-methyl methacrylate (Zonyl-TM-MMA) copolymers were investigated, it was found that the wettability of the films strongly depend on perfluoroalkyl chain lengths. Besides, increase in hydrocarbon chain lengths also caused an increase in contact angle results due to the stronger cohesion interactions of liquid molecules and thus weaker adhesion between the polymer film and the liquid drop3 . Nano particles can also be used to improve the wettability properties of the surfaces. To investigate this affect, perfluoro-styrene copolymers with varying SiO2 nano particle content were prepared. Water drop contact angles increased up to 170° and exhibited extremely superhydrophobic behavior at higher SiO2 contents. However, an opposite behavior was observed with hexadecane drop; increase in both SiO2 and perfluoro- contents have caused a decrease in hexadecane contact angles. While the surfaces that contain higher amounts of SiO2 exhibited superhydrophobic behavior, their oleophobic behavior were reduced with the increase of nano particle content4 . Geometrically patterned surfaces, such as cylindrical pillars, can also be used to prepare liquid repellent surfaces2 . Cylindrical pillars with varying diameters between 10 µm to 100 µm, separation distances between 5 µm to 10 µm, constant heights of 40 µm ± 2 and solid area fractions [fCBs(geo)] between 0.349 to 0.712 were prepared and coated with perfluoro styrene copolymer to improve their liquid repellencies. Oleophobic behaviors of the patterned surfaces were affected from the type of the hydrocarbon liquids used and with the increase of hydrocarbon liquid chain lengths cylindrical pillar surfaces exhibited more oleophobic behavior. Applicability of Cassie-Baxter equation on cylindrical pillar surfaces was also investigated and was found that CA values of both water and hydrocarbon liquids were not obeying Cassie-Baxter theory however in the case of hydrocarbon liquids deviations from the theory were much more larger. Surfaces with liquid repellent properties that were prepared by using perfluoroalkyl copolymers, polymer-nano particle composites and micropatterns, as briefly summarized above, will be reviewed within this presentation.
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