It is a well-known fact that one of the primary modes of transmission of the covid-19 virus is through respiratory droplets. Chances of transmission are also high when these infected droplets land on different surfaces, which are then touched or come in contact with a person. Wiping down and disinfection of different surfaces has now become the norm across the world, but what if a surface could cut down on the virus’ survival time?
Scientists and researchers have become increasingly interested in how droplets dry on impermeable and porous surfaces. Simply put, surfaces that speed up evaporation can bring down the spread of the covid-19 virus or SARS-CoV-2. Now a new study by researchers at the Indian Institute of Technology Bombay, published recently in the Physics of Fluids journal, shows that a droplet remains liquid for a much shorter time on a porous surface, making it less favorable for survival of the coronavirus.
The researchers found the coronavirus can survive for four days on glass, seven days on plastic, and seven days on stainless steel. But on paper and cloth, the virus survived for only three hours and two days, respectively. According to an official release, for both impermeable and porous surfaces, 99.9% of the droplet's liquid content evaporated within the first few minutes. After this initial state, a microscopic thin residual liquid film remains on the exposed solid parts, where the virus can still survive.
The researchers discovered that the evaporation of this remaining thin film is much faster in the case of porous surfaces as compared to impermeable ones. “The droplets spread due to capillary action between the liquid near the contact line and the horizontally oriented fibers on the porous surface and the void spaces in porous materials, which accelerates evaporation,” the release explains. Essentially, it’s the geometric features of the porous material that speed up the process of evaporation of the thin film rather than its chemical properties, the researchers explain.
“Based on our study, we recommend that furniture in hospitals and offices, made of impermeable material, such as glass, stainless steel, or laminated wood, be covered with porous material, such as cloth, to reduce the risk of infection upon touch," Sanghamitro Chatterjee, a co-author of the study, adds in the release. Other co-authors of the study include Janani Srree Murallidharan, Amit Agrawal, and Rajneesh Bhardwaj.
The researchers also suggested that seats in public places, such as parks, shopping malls, restaurants, railway stations and airports could be covered with cloth to alleviate the risk of disease spread.