Scientists have developed a new kind of fluid repellant paper, based on the so-called lotus effect – the behavior of lotus plants that repel liquid through their surface patterns. The new paper was designed by researchers at the Institute of Technology of Georgia and can repel various kinds of liquids such as water and even oil.
The new water repellant paper got scientists excited for its potential as a cheap diagnostic tool in the future, but also for the possibility of creating recyclable packaging materials which are also very affordable.
Scientists say this was probably the first time that a flexible material known for its high capacity to absorb liquids was transformed in something that repels liquids. This was achieved by creating a superamphiphobic (fluid repellant) coating for the paper.
The repellant effect obtained by scientists mimics the behavior of lotus leaves and was achieved by applying chemical coating to the paper and creating nanometer and micron scale surface patterns.
The new paper can be made of softwood or hardwood fibers first ground into smaller structures and then pressed together in the presence of water. But unlike with traditional paper processing methods, the water is removed and the fibers are further treated with chemical butanol. This inhibits the hydrogen bonding that takes place between cellulose fibers, therefore allowing better control of the fibers’ spacing.
In the second stage of the process, scientists used oxygen plasma etching methods, like with microelectronics, to remove the surface cellulose layer, which uncovered smaller cellulose structures. In the final stage, a thin fluoropolymer coating was applied over these cellulose structures, making the paper fluid repellant.
During tests, the paper was able to repel a wide range of liquids, including water, ethylene glycol, motor oil, solvent and others. For the time being, only samples of about 4 inches have been produced, but the Georgia Tech researchers are confident that the process can be easily scaled up.
Researchers have also printed patterns on the modified paper with a desktop printer and hydrophobic ink. Droplets applied to the surface remained on the pattern formed by ink, as they were repelled by the adjacent surface.
This led scientists to believe that the new paper could be the base for a new generation of affordable biomedical diagnostic test tools, in which droplets that contain antigens could be placed on a printed surface and made to encounter various diagnostic chemicals. The use of proper reagents could help determine the presence or absence of disease.
[Image via Georgia Tech]