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MOSCOW, February 25. /TASS /. A research team from the Institute of Theoretical and Experimental Biophysics of the Russian Academy of Sciences and MIPT (Moscow Institute of Physics and Technology) student Andrei Avseenko have synthesized material that is just a perfect filter for protection of respiratory organs, analytical research and other practical purposes.
Figure 1. The structure of the new material. Image was obtained by atomic force microscopy (AFM).The picture is courtesy of the researchers
An almost weightless fabric made of nylon nanofibers with a diameter less than 15 nm beats any other similar materials in terms of filtering and optical properties, MIPT press service said.
The scientists whose work is published in Macromolecular Nanotechnology Journal, characterize their material as lightweight (10-20 mg/m2), almost invisible (95% light transmission: more than that of a window glass), showing low resistance to airflow and efficient interception of <1 micrometer fine particulate matter.
The wording "nanofibers" in the researchers’ article is more than a fashion statement. Previously, the same team demonstrated that reducing fiber diameter from 200 nanometers down to 20 decreased filter resistance to airflow by two thirds, and this effect could no longer be explained by classical aerodynamics. When an obstacle size is smaller than the free path of gas molecules (an average distance one molecule manages to cover before colliding with another), the standard methods estimating aerodynamic resistance based on the continuum theory no longer work. In normal conditions, the mean free path of air molecules makes 65 nanometers.
The scientists used the technique called electrospinning: a jet of a dissolved polymer is ejected through a special nozzle aiming at a target under action of an electric field. From the other side, ethanol is electrosprayed. The polymer jet and the alcohol ions take the opposite electric charges. Colliding in the air, they form ultra-thin fibrous films.
Figure 2. A sample of the new fabric for filters. The small red spot on top of “l” letter is a spot wherea laser beam penetrates the film. Low intensity of dispersed light demonstrates high transparency of the new material. A transmission index of the new product is higher than that of a good window glass.The picture is courtesy of the researchers
The testing of nylon-4,6 electrospun films showed that thess almost weightless and invisible fabrics trap no less than 98% of airborne dust particles. For testing, the scientists used particles from 0.2 to 0.3 micron in diameter. This roughly corresponds to the dust that is not caught by the nasal pharynx, and penetrates the lungs causing a number of dangerous medical conditions. Submicron particles (< 1 micrometer in diameter) are the ones also used to test industrial and medical filters. To assess performance, resistance to airflow is tested as well.
Speaking about possible applications of this material, the scientists claim it is more than the obvious air and water purification from particulate matter. Since the material surpasses glass in transparency, it can be used in biological research. For example, after pumping air or water through the new filter intercepted microorganisms may be directly observed right on the transparent filter under a microscope. Again, this effect is due to ultra-fine threads. Their thickness is significantly less than even visible light wavelength.