The research team in Mechanical Engineering PolyU under Prof. Wallace Leung has developed nanofiber mats that has electrostatic charges deposited on the nanofibers. Nanofiber has diameter which is typically 1/1000 times smaller than a human hair. The charged fiber mat has been applied for air filtration of pollutant particles for all sizes, from sub-micron size (less than 1/1000 of 1 millimeter) down to 10 nanometers (100 times of a hydrogen atom).
With reference to the attached diagram, when a neutrally charged (i.e. no charge) particle is in close proximity to the charged nanofiber, the particle is polarized with an induced positive and also an induced negative charge (a dipole). The charged fiber further attracts the opposite charge of the dipole to effect capture of the particle. Given the electrostatic force varies inversely as the square of the distance, due to the small-diameter nanofiber, the particle can get closer to the fiber thereby experiencing strong electrostatic induction followed-by attraction of the particle.
Larger particles, several hundreds of nanometers (smog size), has higher capture than smaller particle because the induced dipole is stronger by virtue of the larger particle size. Given the electrostatic filtration mechanism has no effect on pressure drop, therefore, smog mask and other air filters (face masks, respirators, etc. ) developed using this technology can enjoy high breathability with low pressure drop, yet with excellent capture efficiency. Further, the charged fibers are arranged in a special way to enhance the charge effect to further excel the performance on air filtration.
Viruses usually carry negative electrostatic charges. The viruses can be captured very effectively by the positively charged nanofiber mat made into a face mask. This would be an ideal defense during virus outbreak.
In addition, the charged nanofiber mat can also be used for western blot for protein identification by transferring protein from a two-dimensional gel containing the original protein sample. Further, it can also be used for drug release where users can inhale released drug once the drug is captured electrostatically by the nanofiber mat. Prof. Leung comments that this is a very exciting, patent-pending, new technology. “We are looking for licensee and partners who might have interest to further explore the commercial application for air filters as well as collaborators to continue the R&D development on non-filtration applications (drug release and western blot, etc.).”