Polyimide-based nanoporous membrane used for developing reusable N95 masks
Surgical grade N95 mask’s filtration efficiency for sub-300 nanometers (nm) particles is around 85%. As the COVID-19 virus shows a diameter of around 65–125 nm, there is a need for developing more efficient masks.
A research team at Saudi Arabia's King Abdullah University of Science and Technology (KAUST) developed a flexible, replaceable nanoporous membrane to achieve a reusable N95 mask with enhanced filtration efficiency.
The nanoporous membrane is made to filter out COVID-19 virus (purple), allowing only clean air (blue) through. (Photo: ACS Nano)
Schematic showing the use of the nanoporous membrane fabricated on an 8-in wafer on a reusable N95 mask after folding it. The membrane can be replaced after every use. (Photo: ACS Nano)
The membrane is polyimide-based. After a porous silicon template was placed over that membrane, a process called reactive ion etching was used to create an array of tiny pores within it.
The size of the pores ranged from 5 to 55 nm which is considerably smaller than COVID-19 virus. To allow for sufficient breathability, those pores were placed no farther than 330 nm apart from one another.
Polyimide has been widely used in aerospace and microelectronics applications and, more recently, in flexible electronics due to its excellent mechanical strength, thermal stability, and chemical properties over a wide range of temperatures (-20°C to 400°C).
Polyimide thin layer coated on a 4-in silicon wafer and cured (left). Polyimide-based nanoporous membrane being released from the wafer (right).
Besides, the membrane is intrinsically hydrophobic (water-repelling), which contributes to antifouling and self-cleaning as a result of droplets rolling and sliding on the inclined mask area.
The membrane is simply applied to the surface of the m N95 ask before each use, then just peeled off and disposed of afterwards.
The research paper was recently published in the journal ACS Nano by American Chemical Society (ACS).
