Penetration and secondary atomization of droplets impacted on wet facemasks

Abstract

Face covering, commonly known as a facemask, is considered to be one of the most effective pieces of personal protective equipment to reduce transmissions of pathogens through respiratory droplets-both large droplets and liquid aerosol particles. Facemasks inhibit the expulsion of such respiratory droplets from the user and protect the user from inhaling pathogen-laden potentially harmful droplets or their dried nuclei. While the efficacies of various dry face masks have been explored in the recent past, a comprehensive investigation of a wet mask is lacking. Yet users wear masks for an extended period and, consequently, due to the deposition of respiratory droplets released through multiple respiratory events, the mask matrix becomes wet. We, herein, present an experimental study on the dynamics of sequential impacts of droplets on masks to understand how wetness affects possible penetration and secondary atomization of the impacted droplet. Two different types of masks, hydrophobic and hydrophilic, were used in this study to evaluate the underlying physical mechanisms that control the penetration in each of them.

Evaluating Droplet Survivability on Face Masks with X-ray Microtomography

“…Additional layers, such as a filtration layer and an extra inner layer, would further prevent viral particles from reaching the user, securely trapped within the layers, and protect the wearer from contamination. 45 For example, an additional inner layer with embedded nanowall structures could limit the movement of tiny droplets due to local hydrophobicity enhancement at a tiny scale. 59 The filter layer, mainly manufactured through meltblown technology, often complements mechanical filtration with electrostatic charges that can trap ultrafine particles.…”

“…Hydrophilic face masks that preferentially absorb moisture show that prewetted conditions can increase filtration efficacy . Notably, hydrophilic layers prevent “beading” droplets from forming at the surface and increase the resistance to subsequential droplet penetration, due to water absorption . As previously stated, shorter drying times in hydrophilic porous substrates will reduce the likelihood of pathogen survivability and risk of infection via fomite since the virus is trapped within the pores.…”

“…44 Notably, hydrophilic layers prevent "beading" droplets from forming at the surface and increase the resistance to subsequential droplet penetration, due to water absorption. 45 As previously stated, shorter drying times in hydrophilic porous substrates will reduce the likelihood of pathogen survivability and risk of infection via fomite since the virus is trapped within the pores. Therefore, addressing the droplet survivability in daily single-use face masks by investigating the droplet evaporation rate relationship with the layer's wettability is crucial in understanding the contamination risk.…”

The Bacterial Burden of Worn Face Masks – Observational Research and Literature Review

“…Lastly, accumulated microorganisms may be distributed via leakage [108][109][110], amplified by the atomiser effect of the mask [15,17,117,171,172].…”

Lessons from the health policies for children during the pandemic in Japan

“…The droplets captured by the mask might be transformed into aerosols and were floated in a chamber. Penetration and secondary atomization of droplets impacted on the surgical masks were also well studied ( 81 , 82 ). People wear masks for a long period of time and, it is considered that, due to the deposition of respiratory droplets released through multiple respiratory events, mask matrix becomes wet and secondary atomization of the droplets was promoted to produce aerosol.…”