Advanced paper could allow for inexpensive biomedical and diagnostic devices
Baku, June 5 (AZERTAC). By modifying the underlying network of cellulose fibers, etching off surface “fluff” and applying a thin chemical coating, Georgia Institute of Technologyresearchers have created a new type of paper that repels a wide variety of liquids — including water and oil.
The paper takes advantage of the “lotus effect” — used by leaves of the lotus plant — to repel liquids through the creation of surface patterns at two different size scales and the application of a chemical coating. The material uses nanometer- and micron-scale structures and a surface fluorocarbon.
The modified paper could be used as the foundation for a new generation of inexpensive biomedical diagnostics in which liquid samples would flow along patterns printed on the paper using special hydrophobic (water-repelling) ink and an ordinary desktop printer. This paper could also provide an improved packaging material that would be less expensive than other oil- and water-repelling materials, while being both recyclable and sustainable.
The new paper, which is both superhydrophobic (water-repelling) and super oleophobic (oil-repelling), can be made from standard softwood and hardwood fibers using a modified paper process.
he desirable properties we are seeking are mainly controlled by the geometry of the fibers,” Hess explained.
The researchers have printed patterns onto their paper using a hydrophobic ink and a desktop printer. Droplets applied to the pattern remain on the ink pattern, repelled by the adjacent superamphiphobic surface. In testing, the paper was able to repel water, motor oil, ethylene glycol and n-hexadecane solvent.
That capability could facilitate development of inexpensive biomedical diagnostic tests in which a droplet containing antigens could be rolled along a printed surface where the droplet would encounter diagnostic chemicals.
Creating a superhydrophobic surface was relatively straightforward because water has a high surface tension. For oils, which have a low surface tension, the key to creating the repellent surface is to create re-entrant — or undercut — angles between the droplets and the surface.
Previous examples of superamphiphobic surfaces have been made on rigid surfaces through lithographic techniques. Such processes tend to produce fragile surfaces that are prone to damage, Hess said.
The new paper has so far been made in samples about four inches on a side, but Hess sees no reason why the process couldn’t be scaled up.
The research has been supported by the Institute for Paper Science and Technology (IPST) at Georgia Tech.
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