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. 2020 Aug 1;32(8):081702.
doi: 10.1063/5.0020249. Epub 2020 Aug 11.

Tailoring surface wettability to reduce chances of infection of COVID-19 by a respiratory droplet and to improve the effectiveness of personal protection equipment

Rajneesh Bhardwaj  1 , Amit Agrawal  1
Affiliations

Tailoring surface wettability to reduce chances of infection of COVID-19 by a respiratory droplet and to improve the effectiveness of personal protection equipment

Rajneesh Bhardwaj et al. Phys Fluids (1994). .

Abstract

Motivated by the fact that the drying time of respiratory droplets is related to the spread of COVID-19 [R. Bhardwaj and A. Agrawal, "Likelihood of survival of coronavirus in a respiratory droplet deposited on a solid surface," Phys. Fluids 32, 061704, (2020)], we analyze the drying time of droplets ejected from a COVID-19 infected subject on surfaces of personal protection equipment (PPE), such as a face mask, of different wettabilities. We report the ratio of drying time of the droplet on an ideal superhydrophobic surface (contact angle, θ → 180°) to an ideal hydrophilic surface (θ → 0°) and the ratio of the maximum to minimum drying time of the droplet on the surfaces with different contact angles. The drying time is found to be maximum if θ = 148°, while the aforementioned ratios are 4.6 and 4.8, respectively. These ratios are independent of the droplet initial volume, ambient temperature, relative humidity, and thermophysical properties of the droplet and water vapor. We briefly examine the change in drying time in the presence of impurities on the surface. Besides being of fundamental interest, the analysis provides insights that are useful while designing the PPE to tackle the present pandemic.

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Figures

FIG. 1.
FIG. 1.
Schematic of the problem considered in the present study.
FIG. 2.
FIG. 2.
Comparison between the normalized mass loss rate (ṁN = ṁ/Rλ) as a function of contact angle (θ) used in the present work and that obtained by the model of Popov. The plot of ṁN for the model of Popov is reproduced by Gelderblom et al.
FIG. 3.
FIG. 3.
Drying time vs contact angle for a water droplet of initial volume 5 nl. These calculations are for ambient temperature of 25 °C and RH = 50%.
FIG. 4.
FIG. 4.
Ratio of drying time of a sessile droplet on a surface (tf) to that of a spherical droplet suspended in air (tf,sph) of the same volume.
See this image and copyright information in PMC

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