BANGALORE: Researchers at the premier Indian Institute of Science (IISc) have developed an artificial surface that can retain its water repellant properties even when kept immersed.
The research team was also able to find a way to control the duration for which the water repellant property was maintained. They were also able to demonstrate that resistance to water flow past the surface is reduced. This can result in diverse applications like better printers and efficient and cheap blood testing.
The paper appeared in the international journal Colloids and Surfaces A: Physicochemical and Engineering Aspects last week. Such materials work because they have special structures on their surface that trap tiny pockets of air.
These tiny air pockets allow water to flow without coming in contact with the surface, and thus flow with reduced resistance. However, if the surface stays in contact with water for a long time, the air dissolves in water, just like in an immersed lotus leaf, and the water-repellent property vanishes.
Prof Bobji MS, an Associate Professor at the Department of Mechanical Engineering, IISc, and his team have discovered a novel way to control the duration for which the air pockets can stay alive longer. The team exploited the fact that the solubility of air in water depends on pressure. At low pressure, water cannot dissolve gases easily -- this is why soft drink bottles are pressurised to keep the carbon dioxide dissolved.
The team has shown that by lowering the pressure, they can even supply air to these pockets, thus prolonging the effect. Prof Bobji says, “What we have demonstrated is that even bubbles of 0.3 mm can be sustained for longer than five hours easily with our “air pump” methodology, resulting in drag reduction of up to 20 per cent.” Efforts are now under way to create large surfaces with similar properties. If successful, submarines that can travel with little effort can be a reality.