Metallic superhydrophobic surfaces surface structuring

Real-world structured surfaces for superhydrophobic electrowetting range from geometrically uniform like those in Figs Id and 2a, to randomly oriented fiberlike structures. Most demonstrated works include a composite dielectric approach. In this composite approach the structured electrode is first insulated with a conventional dielectric such as a metal or semiconductor oxide. The composite dielectric is then completed with a plasma deposited fluorocarbon or solution deposited flu-oropolymer in order to provide adequate hydrophobicity for a stable Cassie state. A brief review of techniques to create superhydrophobic electrowetting surfaces is provided below. The demonstrated structures vary substantially in geometry and materials, however, electrowetting results are somewhat similar across all platforms. 

In recent years, due to a plethora of potential applications of superhydro-phobicity in daily life, many elforts have been taken to fabricate artificial superhydrophobic surfaces. Depending on the application and material, different methods have been employed to create superhydrophobic smfaces [8], Most of these methods involve either creating a micro/ nano-structme on an inherently hydrophobic material [9,10] or treating a specific micro/nano-structure with a hydrophobic coating [11-14]. For instance, for metallic materials, roughened surfaces have to be coated with low surface energy materials. 

Table 3 Quantitative Characterization of Superhydrophobic Metal Surfaces Structured by Ultra-Short Pulsed Laser Irradiation Structure...

The results of the quantitative characterization of superhydrophobic metal surfaces structured by ultra-short pulsed laser irradiation are summarized in Table 3. The water contact angles measured prior to the laser irradiation were 65°—85° on copper, titanium, iron, and aluminum... 

As can be seen from the data presented in Table 3, metal surfaces structured with quasi periodic spikes, as well as irregular combination of micro-and nanoroughness, meet the criteria of superhydrophobic surfaces. 

The presence of several scales on the substrate structure has been recognized to be a necessary condition for superhydrophobicity of materials which are normally easily wetted [8, 14] like chromium (as a metal). For the present case, the surface... 

Based on colloidal monolayers of polystyrene spheres, we have prepared various two-dimensional nano-structured arrays by solution routes and electrodeposition. Many ordered structured arrays generated using these methods are of surface roughness on the nano- and micro-scales, and could be superhydrophobic or superhydrophilic. The nano-devices based on such nano-structured arrays would be waterproof and selfcleaning, in addition to their special device functions. In this article, taking silica, ZnO and gold as examples of the insulators, semiconductors and metals, respectively, we report some of our recent results to demonstrate controlled wettability and superhydrophobicity of two-dimensional ordered nano-stmctured arrays with centimeter square-size based on colloidal monolayers. 

Surfaces containing spike structures show promise for the fabrication of superhydrophobic metallic surfaces due to their particular shape (concave structure with high aspect ratio, covered with nanoroughness). Note that the spikes that have been generated on semiconductor surfaces have been intensively studied in the past, inter alia, because of their superhydrophobic properties (Baldacchini et al., 2006 Zorba et al., 2006,2008). 

Moreover, on superhydrophobic structured metallic surfaces, water droplets can be observed to bounce when dropped onto the surface. The kinetic energy of the falling water droplet is transferred to the surface energy without the droplet spreading, then bounces numerous times before coming to rest. The time lapse pictures presented in Figure 8 show the first two... 

It is noteworthy that the superhydrophobic properties of laser structured metal surfaces with quasi-periodic spikes could be restored by cleaning the samples in acetone using an ultrasonic bath, followed by drying in a desiccator. 

Jagdheesh, R., Pathiraj, B., Karatay E., Romer, G.R.B.E., Huis in t Veld, A.J., 2011. Laser-induced nanoscale superhydrophobic structures on metal surfaces. Langmuir 27, 8464. 

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