Researchers at the Indian Institute of Technology (IIT), Bombay, have developed a technique for coating face shields with a hydrophobic layer to improve their efficiency. This would repel water from the surface of the shields, unlike plastics.
Face shields act as primary barriers to airborne disease-carrying droplets. But these simple face shields are made from plexiglass plastic or polyethylene terephthalate. Plastic is hydrophilic and tiny water droplets tend to stick to its surface. Studies have shown that the SARS-CoV-2 laden respiratory droplets can survive on different surfaces for a few hours to a few days, as per a report in IANS.
When individuals unwittingly touch such surfaces, they are susceptible to infection by fomite transmission. The hydrophilic nature of the face shield increases the chances of fomite transmission, which calls for frequent cleaning and sanitising them.
A team of researchers from IIT-B's Mechanical engineering department proposed a novel technique to enhance the efficiency of face shields by coating them with a hydrophobic (water repellent) layer. The resulting composite face shield acts as a barrier for airborne droplets and repels them; this reduces the risk of fomite formation from the surface of the face shield. The study is published in the journal Physics of Fluids.
Expelled droplets are tiny, about 50-200 microns in size (a micron is one-thousand of a millimetre), and hence, unseen to the naked eye.
To prevent the droplets from sticking on the surface, the team repurposed a commercially available and economical spray used to coat automobile windshields. The spray coating contains silica nanoparticles making the coating superhydrophobic, thereby, keeping the windscreen clear during bad weather conditions.
The researchers coated the face shield with this hydrophobic coating and demonstrated that the face shield could fend off tiny virus-laden droplets. They observed that water droplets falling on the face shield bounced off the surface, keeping the coated area free of water deposit and hence, eliminating fomite accumulation.
The team conducted laboratory experiments to establish the repelling properties of the composite coated face shield.
"In our study, we show how individual droplets behave after coming into contact with the face shield's coated surface," said Rajneesh Bhardwaj, co-author of the study, as quoted in a report by IANS.
Their experiments also show that the coating does not affect the transparency of the face shield. The coated surface also had far less wettability than the uncoated surface.
