Fig. 5.

Filtration mechanisms of masks. (a) The filtration mechanisms of masks generally involve mechanical (MF) and electrostatic filtrations (EF). Adapted with permission from ref. [60]. Copyright 2020 American Chemical Society. (b) Gravity sedimentation, whereby a large particle falls and adheres to a fiber cross-section. The grey particle (top) falls onto the filter and adheres via van der Waals attraction, indicating successful filtration, shown in red. (c) Inertial impaction, whereby a large particle with large inertia travels linearly, eventually coming into contact with a fiber. The grey particle (left) does not follow the streamline around the fiber and is unable to avoid it, adhering and becoming filtered. (d) Interception, whereby a small particle is led to adhere to a fiber by motion along the streamline. (e) Diffusion, whereby Brownian motion of a small particle results in contact and adhesion to a fiber. (f) Electrostatic attraction, whereby a charged particle is trapped on a fiber of opposite charge through electrostatic attraction. Particles shown in b-f were not drawn to scale. Adapted with permission from ref. [59]. Copyright 2021 KeAi Communications Co.