page_title: Ultrahydrophobicity
section_title: Potential applications
hierarchical_section_title: Ultrahydrophobicity / Potential applications
caption_attribution_description: English: A super-hydrophobic paint developed by scientists in UCL Chemistry could have great promise for commercial self-cleaning coatings. It can be applied to many surfaces (in this case, glass), and forms a tough surface that resists abrasion, and repels water extremely effectively. As the water forms a bead and rolls off the surface, it dislodges any dust, dirt, bacteria or viruses that are present. Here, a pattern has been drawn on the glass using the coating, and water is repelled from the painted areas and is restricted to the untreated areas.
context_page_description: Ultrahydrophobic surfaces are highly hydrophobic, i.e., extremely difficult to wet. The contact angles of a water droplet on an ultrahydrophobic material exceed 150°. This is also referred to as the lotus effect, after the superhydrophobic leaves of the lotus plant. A droplet striking these kinds of surfaces can fully rebound like an elastic ball. Interactions of bouncing drops can be further reduced using special superhydrophobic surfaces that promote symmetry breaking, pancake bouncing or waterbowl bouncing.
context_section_description: Active recent research on superhydrophobic materials might eventually lead to industrial applications. Some attempts at fabricating a superhydrophobic surface include mimicking a lotus leaf surface, namely the two-tiered characteristic. This requires micro-scale surfaces with typically nanoscale features on top of them. For example, a simple routine of coating cotton fabric with silica or titania particles by sol-gel technique has been reported, which protects the fabric from UV light and makes it superhydrophobic. Similarly, silica nanoparticles can be deposited on top of already hydrophobic carbon fabric. The carbon fabric by itself is identified as inherently hydrophobic, but not distinguished as superhydrophobic since its contact angle is not higher than 150°. With the adhesion of silica nanoparticles, contact angles as high as 162° are achieved. Using silica nano-particles is also of interest to develop transparent hydrophobic materials for car windshields and self-cleaning windows. By coating an already transparent surface with nano-silica with about 1 wt%, droplet contact angles can be raised up to 168° with a 12° sliding angle.
  An efficient routine has been reported for making linear low-density polyethylene superhydrophobic and thus self-cleaning; 99% of dirt deposited on such a surface is easily washed away. Patterned superhydrophobic surfaces also have the promises for the lab-on-a-chip, microfluidic devices and can drastically improve the surface based bioanalysis. 
  In the textile industry, superhydrophobicity refers to static roll-off angles of water of 20° or less. An example of superhydrophobic effect in live application is the team Alinghi in America's Cup using specially treated sailing jackets. The treatment is built up by micrometre size particles in combination with traditional fluorine chemistry.
  There has been a recent development of super hydrophobic paper which has unique properties for its application in paper based electronics and medical industry. The paper is synthesized in an organic free medium which makes it environment friendly. The paper has antimicrobial properties as it does not hold moisture so it makes it perfect for surgical applications. This paper can be a huge breakthrough for the paper based electronics industry. The resistance to aqueous and organic solvents makes it ideal choice in developing electronic sensors and chips. Skin based analyte detection is now possible without damaging and continuous replacing of the electrodes as this paper will be immune to sweat. With its endless applications this field of material science is sure to be more explored.
  A recent application of hydrophobic structures and materials is in the development of micro fuel cell chips. Reactions within the fuel cell produce waste gas CO₂ which can be vented out through these hydrophobic membranes. The membrane consists of many microcavities which allow the gas to escape, while its hydrophobicity characteristic prevents the liquid fuel from leaking through. More fuel flows in to replace the volume previously kept by the waste gas, and the reaction is allowed to continue.
  A well-known application of ultrahydrophobic surfaces is on heat exchangers, where they can improve droplet shedding and even cause jumping-droplet condensation, with potential for powerplants, heating and air conditioning, and desalination. Rare earth oxides, which are found to exhibit intrinsically hydrophobic surfaces, offer an alternative to surface coatings, allowing the development of thermally stable hydrophobic surfaces for heat exchangers operating at high temperature Ultrahydrophobic desalination membranes for membrane distillation have also been fabricated for improved fouling resistance, which can be fabricated effectively with chemical vapor deposition.
  It has been also suggested that the superhydrophobic surfaces can also repel ice or prevent ice accumulation leading to the phenomenon of icephobicity. However, not every superhydrophobic surface is icephobic and the approach is still under development. In particular, the frost
caption: A test of super-hydrophobic paint.
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