The coronavirus survives on surfaces for hours turning into a film similar to a pancake

Coronavirus-containing particles that land on a surface remain infectious for several days turning into a microscopic pancake-like film after the water in the droplet evaporates.

This conversion sees more than 99.9% of the liquid in the drop vanish within minutes, but the virus survives in a protective film of the remaining fluid.

Small forces keep the film, which is only nanometers thick, adhering to a surface and slow down the evaporation process.

The film evaporates completely at different times, depending on the material it landed on, with a large drop on stainless steel and copper lasting only 24 and 16 hours respectively.

But it can survive for more than 150 hours on polypropylene. A smaller drop, only one-tenth the size, lasts more than 80 hours on the glass.

These figures are based on experiments conducted under laboratory conditions and are likely lower in the real world where there are varying amounts of heat and airflow, factors that increase evaporation.

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The film (bottom) covers the same amount of areas as the drop (top), with the same radius and initial tilt angle. The only measure that changes is its vertical height

Rajneesh Bhardwaj and Amit Agrawal, professors of IIT Bombay, specialize in using computer and physical modeling to understand how coronavirus droplets can spread disease.

Previously, they found that wearing a face mask reduces the size of the clouds of infectious coronavirus particles created by a cough by up to 23 times.

Coronavirus-containing particles from sneezing and coughing that land on a surface remain infectious for several hours because the water in the droplet evaporates and turns from a sphere into a microscopic pancake-like film (broth)

In the form of a film, the coronavirus can resist for several hours, and even days, on hydrophobic surfaces if left undisturbed.

The film covers the same amount of areas as the droplet, with the same radius and initial tilt angle. The only measure that changes is its vertical height.

The study data, published in Physics of Fluids, found that film thickness slowly decreases as long as and throughout this time the amount of coronavirus in the droplet / film is constant.

“Our biggest surprise was that the drying time of this nanometer film is on the order of hours,” Bhardwaj said.

‘This suggests that the surface is not completely dry and the slowly evaporating nanoscale film is providing the means necessary for the coronavirus to survive.’

The researchers say their results indicate that the virus can survive in a viable form for a long period of time and stressed the need for regular and thorough cleaning of surfaces.

“It is desirable to disinfect frequently touched surfaces, such as doorknobs or portable devices, and inside hospitals and other epidemic areas,” Agrawal said.

‘We also recommend that surfaces be heated, because even short-lived high temperatures, at which the surface is at a higher temperature than ambient, can help evaporate the nanometer film and destroy the virus.’