SUPER HYDROPHOBIC COATING

Lotus effectSuperhydrophobicity is a property that governs the extreme water repellence and non wettability of a solid surface. On such surfaces water or any other liquid forms nearly spherical droplets and not continuous films.-Example:-Lotus leaves.

An environmental scanning electron water droplet adopt an spherical microscopic Image of the famed Lotus leaf shape on waxy layer

Parameters for superhydrophobic coating1. Contact angle- surfaces are highly hydrophobic i.e., extremely difficult to wet.

The contact angles of a water droplet exceed 150° 2. Angle of slide- Another feature is that the surfaces must have a

low angle of slide less than 10 degree , measured from the horizontal i.e. the water droplets should roll down the surface very easily, similar to rolling of rigid spheres.

3. Self cleaning ability- Superhydrophobic coatings or surfaces the adhesion between the water droplets and the dust particles is much more than that between the surface and the dust.

4. Elastic collision of liquid- Water droplets which fall on a superhydrophobic surface with some velocity can bounce back, practically without any deformation after having suffered an almost elastic collision

Super Hydrophobic Coating

The process of coating the surface of a material with hydrophobic property material in order to avoid sticking of liquids on that surface.Super hydrophobic technology makes water bounce, it stops it, rolls it off the surface

Various methods are used for the preparation of rough surfaces:-

1) layer-by-layer And Self assembly2) sol–gel processing3) Etching4) Electro-spinning Method5) electrochemical deposition. 6) chemical vapor deposition.

1) Layer-by-layer self-assembly:- It is a simple and cheap method to construct thin-film coatings by depositing alternating layer.TiO2 and SiO2 coated steel surfaces containing micro- and nanoscale with different surface roughness were fabricated by means of a layer by layer deposition process .

SEM images of different layers of TiO2 nano particles in steel surface: (a) Water droplets on the treated steel surface. (b) TiO2 one layer (TiO2) 1. (c) TiO∗ 2 two

layers (TiO2) 2 and (d) TiO∗ 2 three layers (TiO2) 3∗ 2)Sol–gel process:-

The roughness of the surface obtained with this process can be easily modified simply by changing the composition of the reaction mixture.

Sol–gel processes can produce rough surfaces on a variety of oxides such as silica, alumina, and titania.3) Etching:-Etching is another simple and efficient method to produce super hydrophobic coatings with rough surfaces. Chemical Etching:- A super hydrophobic surface was fabricated by chemical etching (HCl) on aluminum alloy Superhydrophobic coating can be made from many different materials.

Manganese oxide polystyrene (MnO2/PS) nano-composite

Zinc oxide polystyrene (ZnO/PS) nano-compositePrecipitated calcium carbonateSilica nano-coating

Coating applicationAnti foulingAnti condensationAnti frictionAnti iceAnti corrosionTechnological challenges:-1. Textiles 2. Glass

Applications sample:-

Coated cables Uncoated cables Modified SH Uncoated sample coatingConclusion:- 1. Surface roughness increases hydrophobicity 2.Superhydrophobic if contact angle > 150°3. Superhydrophobicity leads to self-cleansing 4. Several methods reported to synthesize artificial superhydrophobic surfaces, but yet it is only in lab scale.References-