# Why coronavirus survives longer on impermeable than porous surfaces

## TL;DR

The paper explains why coronaviruses survive longer on smooth surfaces compared to porous ones like cloth or paper.

## Contribution

The study reveals how capillary imbibition and faster film evaporation on porous surfaces reduce virus survival.

## Key findings

- Porous surfaces experience faster droplet mass loss due to capillary imbibition.
- Thin liquid films on porous surfaces evaporate faster, reducing virus survival time.
- Faster evaporation on porous surfaces is due to increased disjoining pressure from spreading and voids.

## Abstract

Previous studies reported that the drying time of a respiratory droplet on an impermeable
surface along with a residual film left on it is correlated with the coronavirus survival
time. Notably, earlier virus titer measurements revealed that the survival time is
surprisingly less on porous surfaces such as paper and cloth than that on impermeable
surfaces. Previous studies could not capture this distinct aspect of the porous media. We
demonstrate how the mass loss of a respiratory droplet and the evaporation mechanism of a
thin liquid film are modified for the porous media, which leads to a faster decay of the
coronavirus on such media. While diffusion-limited evaporation governs the mass loss from
the bulk droplet for the impermeable surface, a much faster capillary imbibition process
dominates the mass loss for the porous material. After the bulk droplet vanishes, a thin
liquid film remaining on the exposed solid area serves as a medium for the virus survival.
However, the thin film evaporates much faster on porous surfaces than on impermeable
surfaces. The aforesaid faster film evaporation is attributed to droplet spreading due to
the capillary action between the contact line and fibers present on the porous surface and
the modified effective wetted area due to the voids of porous materials, which leads to an
enhanced disjoining pressure within the film, thereby accelerating the film evaporation.
Therefore, the porous materials are less susceptible to virus survival. The findings have
been compared with the previous virus titer measurements.