Science & Technology

COVID Aerosol Filtration: Nanofiber Face Masks Improve Efficiency, Need Replacing More Often

Polyacrylonitrile nanofiber mesh earlier than (left), throughout (center), and after (proper) capturing water aerosols. The mesh turns into coarser as some nanofibers stick collectively after the captured water droplets are absolutely evaporated. Credit score: Southern College of Science and Expertise, Shenzhen, China

Movies seize nanofiber habits below water aerosol publicity.

Since its outbreak, the COVID-19 virus has contaminated greater than 220.9 million individuals worldwide and has claimed greater than 4.5 million lives, in keeping with the World Well being Group coronavirus dashboard as of September 7, 2021.

Nevertheless, many medical professionals attribute the consequential function of face masks in slowing the unfold of the virus and defending human well being.

Improvements to enhance masks efficacy, with growing give attention to nanofiber manufacturing, have resulted in increased filtration effectivity, better consolation, and simpler respiration capability. Nevertheless, the results of microwater droplets on the integrity of nanofibers are comparatively unclear.

In Physics of Fluids, by AIP Publishing, researchers from Southern College of Science and Expertise in Shenzhen, China, study these ambiguities by way of a visualization of nanofibers interacting with water aerosol publicity.

The video reveals the polyacrylonitrile (PAN) nanofiber mesh capturing water aerosols. The mesh turns into coarser as some nanofibers stick collectively after the captured water droplets are absolutely evaporated. Credit score: Southern College of Science and Expertise, Shenzhen, China

“When COVID-19 first hit, face masks had been in extraordinarily brief provide in every single place, and other people got here up with every kind of the way to ‘rejuvenize’ used face masks. It was like a chef’s contest, with boiling, steaming, grilling, and even smoking concerned,” stated co-author Boyang Yu. “Our instinct advised us this may’t be proper. We now have to look into it and see what precisely occurred with the nanofibers.”

Yu and his colleagues used high-speed microscopic movies to systematically visualize the evolution of nanofibers made from polymers with totally different contact angles, diameters, and mesh sizes below water aerosol publicity.

“Filming nanofibers is like taking portraits of infants,” stated Yu. “They don’t like to remain in place for the digicam. It is because nanofibers are very tender and flimsy, particularly with the aerosol stream blowing by way of. However with sufficient care, endurance, and luck, we ultimately received good pictures for our evaluation.” 

The pictures produced reveal nanofibers coalesce irreversibly in the course of the “droplet seize stage” in addition to the next liquid evaporation stage, considerably decreasing the efficient fiber size for capturing aerosols. They present hydrophobic and orthogonally woven fibers can scale back capillary forces and reduce the fiber coalescing fee.

“We confirmed three issues,” stated co-author Weiwei Deng. “One, nanofibers are very good at capturing droplets in aerosol. Two, the nanofibers are bonded collectively after the aerosol is captured. And three, this bonding is tight and irreversible, even after the captured droplets evaporate.

“Wetted fibers are likely to bond to one another in the identical means that moist hairs are likely to bundle collectively. It’s due to the capillary pressure, which turns into dominant as the dimensions scale shrinks, and this can be very sturdy for nanofibers.”

The research’s findings are anticipated to assist enhance design, fabrication, and use of face masks made with nanofibers. They supply direct visible proof for the necessity to exchange face masks steadily, particularly in chilly environments.

“The winter is coming,” stated Deng. “When it’s chilly exterior, your breath incorporates extra droplets that will make the nanofiber mesh collapse extra rapidly.”

Reference: “Visualization of the interplay of water aerosol and nanofiber mesh” by Boyang Yu, Jian Chen, Daner Chen, Rouxi Chen, Yuenan Wang, Xiujuan Tang, Hsing-Lin Wang, Lian-Ping Wang and Weiwei Deng, 7 September 2021, Physics of Fluids.
DOI: 10.1063/5.0061847

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