New research published today in Physics of Fluids explores the drying times of COVID-19 on different think liquid film surfaces. In the study, authors Rajneesh Bhardwaj and Amit Agrawal, explain London-van der Waals forces interact to allow the virus to cling to surfaces and allow for hours, instead of seconds.
"To describe this thin film, we used tools that are otherwise seldom used by researchers within the engineering realm," said Bhardwaj. "Specifically, we developed a computational model for the evaporating mass rate of the film as a function of disjoining and Laplace pressures inside the film, using the Hertz-Knudsen law, a well-established kinetic theory of gases."
COVID-19 has been shown to be unlike typical respiratory droplets, which persist on surfaces for an average of seconds. "Our model for the thin film transport shows that survival or drying time of a thin liquid film on a surface is on the order of hours and days, similar to what has been observed in measurements of the virus titer [the lowest concentration of virus that still infects cells]," added Agrawal. "It captures the relatively longer survival time on plastic and glass compared to metals."
Improving our scientific comprehension of the virus’s ability to persist on different surfaces under ambient conditions can provide crucial information for developing policies that protect public health and safety.
"Our biggest surprise was that the drying time of this nanometric film is on the order of hours," said Bhardwaj. "It suggests the surface isn't completely dry, and the slowly evaporating nanometric film is providing the medium required for the survival of the coronavirus."
As one might expect, this points again toward the need to be constantly disinfecting surfaces that are frequently touched, such as phones, keys, doorknobs, and light switches.
"We also recommend heating surfaces, because even short duration high temperatures, at which the surface is at a higher temperature than the ambient, can help evaporate the nanometric film and destroy the virus," advise the authors.