A polymeric coating that is extremely water-repelling (superhydrophobic) and will allow water to roll off from the surface like in the case of a lotus leaf or stick to the surface as in the case of rose petals has been synthesised by a two-member team from the Indian Institute of Technology (IIT) Guwahati, The Hindu reported.
It can be spray-coated on various surfaces (glass, plastic, metal, wood and concrete) of diverse chemical composition, texture (smooth or rough surface), geometry (plain sheet or complex shape such as shoes), and size.
The researchers led by Dr. Uttam Manna of Chemistry department of the institute found the water-repelling property of the coating remained intact even when subjected to severe physical and chemical abuse.
By modulating the functionality of the coating with small amine molecules, the coated surface was made to behave either as non-adhesive superhydrophobic coating (where water rolls off as in a lotus leaf) or adhesive superhydrophobic coating where the droplets stick to the surface like in the case of rose petals. The results were published in the Journal of Materials Chemistry A.
“There is a fundamental difference in the way the trapped air is present at the interface between the surface and water droplets and this makes the coated surface either adhesive or non-adhesive superhydrophobic,” says Dr. Manna.
In the case of the non-adhesive superhydrophobic coating, the trapped air is continuous and uniformly distributed. This leads to the trapped air minimising the contact area between the water droplet and the substrate. With adhesive superhydrophobic coating, the trapped air is not continuous and the contact area between the water droplet and the substrate is more thereby causing the droplets to stick to the surface up to 20 degrees tilt angle.
The superhydrophobic coating was prepared by mixing a polymer (branched poly(ethyleneimine)) and a reactive small molecule (dipentaerythritol penta-acrylate) in different alcoholic solvents — ethanol to pentanol.
“We were able to achieve a stable coating only when pentanol solvent was used,” says Dr. Manna.
The polymer and the small molecule react rapidly in the presence of pentanol.