COVID-19 virus survives on surfaces in a thin film

How does the COVID-19 virus manage to survive on surfaces? To find out, Indian researchers are exploring the drying times of thin liquid films that linger on surfaces after most respiratory droplets evaporate.

While the drying time of typical respiratory droplets is on the order of seconds, the survival time of the COVID-19 virus on different surfaces in recent experiments has been found to be on the order of a few hours. This discrepancy suggests a difference of several orders of magnitude in time between the drying of the droplets and the survival time of the COVID-19 virus on surfaces.

In Fluid physics, Rajneesh Bhardwaj and Amit Agrawal, professors at IIT Bombay, describe how a liquid film nanometers thick adheres to the surface, due to the forces of London-van der Waals, which allows the COVID-19 virus to survive for hours.

“To describe this thin film, we used tools that are otherwise rarely used by researchers in the engineering field,” said Bhardwaj. “Specifically, we have developed a computational model for the mass rate of film evaporation as a function of the Laplace disjunction and pressures inside the film, using Hertz-Knudsen’s law, a kinetic theory well established throttle. “

The nanometric film is supposed to be like a pancake deposited on a surface. The researchers briefly looked at the changes in drying time depending on the contact angle and type of surface.

“Our thin film transport model shows that the survival or drying time of a thin liquid film on a surface is of the order of a few hours and days, similar to what was observed in measurements of the virus titer. [the lowest concentration of virus that still infects cells]”said Agrawal.” It captures the relatively longer survival time on plastic and glass compared to metals. “

The ability to predict the survival of a coronavirus on different surfaces can help prevent and contain the spread of COVID-19. This work provides information on how the COVID-19 virus survives for hours or days on solid surfaces under ambient conditions.

“Our biggest surprise was that the drying time for this nanoscale film is on the order of a few hours,” Bhardwaj said. “This suggests that the surface is not completely dry and that the slowly evaporating nanoscale film provides the medium necessary for the coronavirus to survive.”

Since a longer survival time of the virus corresponds to an increased chance of becoming infected, “it is desirable to disinfect frequently touched surfaces, such as doorknobs or portable devices, and in hospitals and the like. areas prone to epidemics, ”Agrawal said.

“We also recommend heating the surfaces, because even short-lived high temperatures, where the surface is at a higher temperature than room temperature, can help evaporate the nanoscale film and destroy the virus.”