During the pandemic, masks have become a part of our everyday outfits, with surgical and cloth masks often used. However, they aren’t designed to filter out microscopic airborne particles. Now, if you want to know what makes a great mask, then look no further than the N95.
Contrary to popular belief, an N95 mask does not work like a strainer—it’s not just a mesh of fibers with gaps too small for microscopic airborne particles to pass through. On the contrary, it utilizes fibers that capture particles using Van der Waals forces, which are electrostatic attractive forces that make uncharged molecules attracted to each other. Basically, N95 masks can attract airborne particles due to forces that cause these microscopic particles to “stick” to the fibers. As an analogy, you can think of the fiber layers of N95 masks as spider webs that can catch anything as long as contact is made. This allows it to filter out particles that are much smaller than the gaps between its fibers.
A point of interest is that N95s were designed by considering the trajectories of different-sized particles. Particles larger than one micrometer generally travel in straight lines due to their inertia and are guaranteed to make contact with a fiber due to the straight path that they take. Meanwhile, particles smaller than 0.1 micrometers are so light that they collide with air molecules and bounce around, causing them to move in random zigzag patterns; this increases the chances of them coming into contact with a fiber. The hardest particles to filter are medium-sized molecules around 0.3 micrometers in size, since they tend to flow along with the air, past the fibers.
However, N95 masks have one more ace up their sleeve. Due to the electric fields they produce, N95 mask fibers can cause internal electrical imbalances in molecules of all sizes, attracting them to fibers that are permanently electrically charged. These charged fibers can capture ten times as many molecules as compared to normal, uncharged fibers. Some medium-sized particles, however, do manage to pass through all these barriers. In fact, this is indicated by its name. “95” signifies that 95% of all medium-sized particles can be successfully filtered by the mask, while 5% manage to pass through.
In conclusion, an N95 mask is not like a strainer; instead, it can be likened to a sticky spider web. Due to its clever design that accounts for many factors, such as the motion of particles of different sizes, the presence of Van der Waals forces, and the electrostatic imbalances that can be caused in neutral molecules, it is able to effectively protect wearers from airborne particles.
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