Superhydrophobic Aluminum Surfaces: Preparation Routes, Properties and Artificial Weathering Impact

Among the materials that can be treated in order to impart superhydrophobic properties are many originally hydrophilic metals. For this, they must undergo a sequential treatment, including roughening and hydrophobic coating. This contribution presents various preparation routes along with various characterization methods, such as dynamic contact angle (DCA) measurements, scanning electron microscopy (SEM) and spectroscopic techniques (FT–IRRAS, XPS, EIS). Micro-rough surfaces of pure and alloyed aluminum were generated most easily by using a modifie Sulfuric Acid Anodization under Intensifie conditions (SAAi). This produces a micro-mountain-like oxide morphology with peak-to-valley heights of 2 μm and sub-μm roughness components. Additionally, micro-embossed and micro-blasted surfaces were investigated. These micro-roughened initial states were chemically modifie with a solution of a hydrophobic compound, such as the reactive f uoroalkylsilane PFATES, the reactive alkyl group containing polymer POMA, or the polymer Teflo ® AF. Alternatively, the chemical modificatio was made by a Hot Filament Chemical Vapor Deposition (HFCVD) of a PTFE layer. The latter can form a considerably higher thickness than the wet-deposited coatings, without detrimental leveling effects being observed in comparison with the original micro-rough surface. The inherent and controllable morphology of the PTFE layers represents an important feature. The impacts of a standardized artificia weathering (WTH) on the wetting behavior and the surface-chemical properties were studied and discussed in terms of possible damage mechanisms. A very high stability of the superhydrophobicity was observed for the f uorinated wet-deposited PFATES and Teflo ® AF coatings as well as for some of the PTFE layer variants, all on SAAi-pretreated substrates. Very good results were also obtained for specimens produced by appropriate mechanical roughening and PTFE coating