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Influence of surface topography and chemistry on the wetting behavior of laser-patterned, metallic surfaces

Subject Area Coating and Surface Technology
Term from 2020 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 435334669
 
Final Report Year 2024

Final Report Abstract

The wetting of technical surfaces has gained growing interest recently due to its great impact on a broad variety of technical relevant phenomena: Wetting influences corrosion behavior, bonding of surfaces with other materials like glue, paint or other metals, antimicrobial properties as well as cell adhesion and tribological performance. The wettability itself, on the other hand, is influenced by factors such as surface topography and chemistry. The roughness of a sample often determines transitions ranging from complete wetting of all structures (Wenzel type), through a variety of mixed states, to wetting only the roughness peaks with air inclusions in the roughness valleys (Cassie-Baxter type). Besides topography, chemistry can show a pronounced influence on the wetting behavior due to a polar surface termination leading to hydrophilicity or nonpolar surfaces depicting hydrophobicity. The project aimed at providing new insight into the role of both – chemical and topographical – influences on the wetting behavior. Copper was chosen as a model material due to its strong application in different sectors (heat transfer, antimicrobial surfaces, corrosion protection, electrical connectors…). Metallographic preparation is the basic for every subsequent sample modification, which is why a preparation and cleaning protocol was established in the first place. Wetting characterization was conducted by static contact angle (SCA) measurements – the most popular method for wetting analysis. A detailed study about preparation and measurement induced influences on SCA measurements was conducted in order to set standards for subsequent characterizations in the project and for the scientific community and to identify relevant parameters like sample packaging and storage. Especially sample storage showed significant influence on the SCA due to the adsorption of volatile hydrocarbon groups which were analysed in detail by XPS and TOF-SIMS. Before producing complex surfaces by direct laser interference patterning combining anisotropic hierarchical topography with oxidic chemistry modification, fundamental relations between the wetting behavior and intrinsic material properties like grain size and deformation were found to especially influence freshly prepared surfaces. In a final study, the gained knowledge was implanted to conduct a complex multi-scale study on the wetting behavior of copper. Influence of aging, oxidic state, isotropic as well as anisotropic topography by DLIP was analyzed experimentally and gives a profound insight into the wetting dynamics of water on copper.

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