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

Abstract

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.

Development of a superhydrophobic polyurethane-based coating from a two-step plasma-fluoroalkyl silane treatment

“…A number of methods are available for achieving the multi-level roughness which, as mentioned, is critical to achieving superhydrophobicity. Examples of roughening mechanisms include: abrasive media; acid etching, and anodising [27], [32].…”

Surface Wettability of Macroporous Anodized Aluminum Oxide

“…44 Surface modifications of anodized aluminum by silanes also proved successful in the formation of (super)hydrophobic aluminum surfaces. 36,45,46 Surface wettability of AAO structures has merely been studied in recent years. Yet, the number of literature reports on the wetting of AAO surfaces is limited and most of the studies were focused on their surface modification with low surface energy materials rather than systematically addressing the wetting of the inherently porous AAO architectures.…”

“…In other works, various AAO structures were used as templates to replicate polytetrafluoroethylene polymeric materials displaying superhydrophobicity , and to obtain well-ordered polymer nanostructures and biodegradable nanorod arrays as well as polymer nanostructures with a wettability transition from wetting to nonwetting . Surface modifications of anodized aluminum by silanes also proved successful in the formation of (super)hydrophobic aluminum surfaces. ,, …”

Superhydrophobic Alumina Surfaces Based on Polymer‐Stabilized Oxide Layers

“…[9,10] By applying this procedure it is possible to produce parts of any size and nearly any shape with such a surface morphology, which is suitable to change their wetting behavior to superhydrophobicity. [7,9,10] The synthetic strategy of this work was to furnish the alumina layer with a coating film consisting of the hydrophilic polymer CHS, which offers a number of functional reactive groups.…”

“…On the other hand, there are also numerous synthetic concepts to furnish polar materials with superhydrophobic properties. [3,7] Particularly, the modification of metal and metal oxide surfaces to impart superhydrophobic properties to these surfaces can be considered as a challenge because these surfaces are typical highenergy surfaces, where physically adsorbed water is always present. Water droplets spread immediately and wet the metal oxide surface completely.…”