Tunable Polymer Membranes

Take a close look at an average polymer membrane, and you'll find a landscape riddled with channels and pores. The size and shape of those features determine how well the material filters out various ions and molecules. Young Moo Lee of Hanyang University, Seoul, South Korea, and an international team of researchers now have developed a type of polymer membrane that provides 100 times better throughput and selectivity than membranes made with conventional polymers (Science 2007, 318, 254). The new membrane could have applications in gas separation, organic batteries, or fuel cells. Key to the material's performance are its uniform bottleneck-shaped pores, which are reminiscent of cellular ion channels. These slim passages let linear CO₂ slide through while keeping bulkier CH₄ out. Lee's team creates the tiny structures through the rearrangement of aromatic polyimides. Upon heating, the polyimides transform into more spatially confined meta- or para-substituted phenylene-heterocyclic ring polymeric structures (meta shown). The pore size can be further tailored by adding acidic dopants, such as HCl or H₃PO₄.