Scientists at the Georgia Institute of Technology have produced a new kind of paper that repels a range of liquids, including water and oil. The new paper shows significant promise as an affordable and recyclable packaging material, but it's the paper’s potential as an inexpensive biomedical diagnostic tool that has really got the researchers excited.

By applying a chemical coating and creating new surface patterns at the nanometer and micron-scale, the researchers are able to reproduce the same repellent effect in the paper that is observed in the leaves of the lotus plant. This changes the paper from an absorbent material to one which repels all fluids.

"Paper is a very heterogeneous material composed of fibers with different sizes, different lengths and a non-circular cross-section," explains Dennis Hess, a professor in the Georgia Tech School of Chemical and Biomolecular Engineering. "We believe this is the first time that a superamphiphobic surface – one that repels all fluids – has been created on a flexible, traditional and heterogeneous material like paper."

The paper can be produced from standard softwood and hardwood fibers, and its manufacture involves breaking cellulose into even smaller structures by using a mechanical grinder, before it is pressed in water (as is the case in traditional paper manufacturing). The water is then removed, and chemical butanol is used to inhibit the hydrogen bonding of the cellulose fibers. This affords the scientists better control of the bonding, which is key to producing the desired repellant effect.

The cellulose material is further subjected to an oxygen plasma etching process which removes the absorbent cellulose surface material and exposes a second, rougher level, which sports the necessary geometry to repel liquids. Finally, a thin coating of a fluoropolymer (Teflon) is also applied.

The researchers printed patterns onto their paper with hydrophobic ink and a desktop printer. Fluid droplets introduced to the pattern remained in place, repelled by the adjacent fluid-repellant surface. This suggests that the paper could perform as a diagnostic tool in the future.

According to the research team, antigens could be passed in liquid form across the printed patterns, which would also, crucially, contain diagnostic chemicals too. The interaction between the diagnostic chemicals and the antigens could indicate the presence of a disease.

So far, the new paper has only been produced in samples of roughly four inches (10 cm) on a side, but the researchers are confident that the process can be scaled-up.

The research has been published in the journal ACS Applied Materials & Interfaces.

Source: Georgia Tech

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