Left: the electron density isosurface from theoretical DFT calculations. S and W atoms are shown in yellow and blue respectively. Right: transmission electron microscopy image. Courtesy: R Boya
Topics: Fluid Mechanics, Materials Science, Nanofluidics, Nanotechnology
Gases flow through a porous membrane at ultrahigh speeds even when the pores’ diameter approaches the atomic scale. This finding by researchers at the University of Manchester in the UK and the University of Pennsylvania in the US shows that the century-old Knudsen description of gas flow remains valid down to the nanoscale – a discovery that could have applications in water purification, gas separation, and air-quality monitoring.
Gas permeation through nano-sized pores is both ubiquitous in nature and technologically important explains Manchester’s Radha Boya, who led the research effort along with Marija Drndić at Pennsylvania. Because the diameter of these narrow pores is much smaller than the mean free diffusion path of gas molecules, the molecules’ flow can be described using a model developed by the Danish physicist Martin Knudsen in the early decades of the 20th century. During so-called Knudsen flow, the diffusing molecules randomly scatter from the pore walls rather than colliding with each other.
Until now, however, researchers didn’t know whether Knudsen flow might break down if the pores become small enough. Boya, Drndić, and colleagues have now shown that the model holds even at the ultimate atomic-scale limit.
Gas flows follow conventional theory even at the nanoscale, Isabelle Dumé, Physics World