The multipurpose hybrid material prevents E. coli growth and is hydrophobic. 

Now, paper or other materials coated with a hydrophobic hybrid molecular material synthesised by researchers at the Indian Institute of Science Education and Research (IISER) Kolkata can behave like a lotus leaf and keep the surface clean and water-proof. Besides increasing the mechanical strength of the coated paper by 1.5 times, the molecular material can inhibit bacterial growth and even render the coated material such as wood fire-proof. The results of the study were published in the journal ACS Omega.

The organic-inorganic hybrid material was synthesised by combining polyhedral oligomeric silsesquioxane (POSS) and diphenylalanine. The POSS molecule by itself has unique properties such as high thermal stability and fire retarding ability. While both POSS and diphenylalanine are naturally water repelling, the hydrophobic nature gets enhanced when they are combined.

“The contact angle of paper, which was 62 degree before coating, increased to 113 degree after coating and became hydrophobic,” says Krishnendu Maji from the Department of Chemical Sciences, IISER, Kokata and the first author of the paper.

To demonstrate the effect of the hybrid material’s hydrophobic nature, the two-member team led by Prof. Debasish Haldar from the Department of Chemical Sciences, IISER, Kolkata folded an ordinary paper and a hybrid-coated paper and drenched the two pieces in water. While the paper without any coating could not be unfolded, the coated paper could be unfolded and regain its original shape.

Corrosion resistance

Testing the hydrophobic nature of the hybrid material and its ability to prevent corrosion, the researchers coated iron nails with the hybrid molecular material and exposed it to water. While the nails that were not coated rusted, those with the coating did not. Coating one half of the nail with the hybrid material, the team found the uncoated portion of the nail rusted in about 12 hours when treated with water; the coated portion remained rust-free. “The coated nails did not get rusted when treated with water for up to one month,” Mr. Maji says.

The coated nails were able to resist corrosion even when treated with an aqueous solution of sodium chloride, potassium chloride, sodium bromide and even hydrochloric acid.

The hybrid material is colourless and does not react with metal. The coated silver artefacts were able to resist the formation of black colour (silver sulphide) on its surface when treated with hydrogen sulphide for 10 minutes. “This hybrid material can protect artefacts from environmental pollution and corrosion,” says Prof Haldar, the corresponding author of the paper.

The coated paper was found to inhibit bacterial growth. While the researchers observed E. coli growing on the surface of paper that was not coated, the hybrid-coated paper was able to inhibit E. coli growth for 10 days. “We tested the anti-bacterial property for up to 30 days and found the hybrid-coated paper was able to resist E. coli growth,” Mr. Maji says.

Fire-retardant property

Finally, the fire-retardant property of matchsticks coated with the hybrid material was tested. While matchstick with no coating burnt completely, fire took more time to reach the end of the matchstick when coated with only POSS. But matchsticks coated with the hybrid material were able to extinguish the flame as soon as fire reached the coated portion. “The peptide not only retards the flame but also extinguishes the fire,” they write.

“Plenty of accidents take place when people throw lighted matchsticks.  By coating a portion of matchsticks with the hybrid material, such accidents can be prevented,” Mr. Maji says.

Published in The Hindu on July 15, 2017