Aluminum sheets were furnished with a water‐repellent composite layer consisting of microroughened alumina, chitosan (CHS), and poly[octadecene‐alt‐(maleic anhydride)] (POMA). CHS was electrochemically deposited or spin‐coated. In a subsequent reaction step, POMA was covalently bonded onto the immobilized CHS layer. The produced composite layers showed superhydrophobic properties, which are indicated by the water contact angles >150° and negligible hysteresis. Cross‐linking reactions of the CHS layer were able to enhance the layer stability. The superhydrophobic surface properties were also maintained after abrasion of the protruding polymer‐coated alumina peaks. This is due to a CHS/POMA reservoir incorporated in the microroughened alumina surface region.magnified image

Among the materials that can show superhydrophobic properties are hydrophilic metals which must undergo a sequential treatment, including roughening and hydrophobic coating. This contribution presents various preparation routes along with characterization work employing dynamic contact angle measurements (CA), scanning electron microscopy (SEM) and spectrometric techniques (FT-IRRAS, XPS, EIS).Micro-rough surfaces of pure and alloyed aluminum were generated most easily by using a special sulfuric acid anodization (SAAi), which produces a micro-mountain-like oxide morphology with peak-to-valley distances of 2 µm and sub-µm roughness components. Additionally, micro-embossed and micro-blasted surfaces were involved. These initial states were combined with a number of dissolved compounds both of low-molecular and of polymer nature, such as the reactive fluoroalkyl silane PFATES, the reactive alkyl group containing polymer POMA, and Teflon ® AF. The chemical modification was alternatively done by the Hot Filament Chemical Vapor Deposition of a PTFE layer. The latter can form a fundamentally higher thickness than the wet-born coatings, without any leveling of the subjacent microprofile. The inherent and controllable morphology of the PTFE layers represents an important feature. Further, the impacts of a standardized artificial weathering onto the wetting behavior and the surface-chemical properties were studied and discussed in terms of possible damage mechanisms. A very high stability of superhydrophobicity was observed with the fluorinated wet-born coatings PFATES and AS/TAF as well as with the PTFE variant AC, each on SAAipretreated substrates. Very good results were also gained for specimens produced by appropriate mechanical roughening and PTFE coating.

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