Sieving gases with twisty polymers

Whether the goal is to capture carbon dioxide (CO2), recover gas from an industrial process, or separate air into its components, there is a need for energy-efficient gas separations. An attractive option is the use of thin films, or membranes, that allow some gases to flow through more easily than others. Polymers are often used to fabricate these membranes because of their processability, but it has been a struggle to create something that can satisfy the levels of performance required for practical and large-scale operations. On page 1390 of this issue, Lai et al. (1) report how exceptional selectivity for one gas over another can be achieved in polymer membranes while allowing very easy passage of the chosen gas. The authors offer a way to improve and tune the selectivity of polymer membranes by simply “aging” them under ambient temperature and pressure over a long period of time (see the figure).