Fast-Flowing Filters

Abstract

MATERIALS SCIENCE Porous membranes are used extensively for separation processes such as water purification. A current challenge is to fabricate membrane materials that can separate objects differing in size by only a few nanometers (which means small pores) and can still operate at a reasonable filtration rate (small pores are prone to blockage). Akthakul et al . have enhanced the filtration capabilities of a commercial poly(vinylidene fluoride) (PVDF) membrane by spin coating a thin film of a copolymer consisting of a PVDF backbone, with short polyethylene oxide (PEO) side chains grafted on via a methacrylate linkage. The PEO and PVDF segments do not like to mix with each other, so the chains segregate locally into partially crystalline PVDF regions separated by PEO nanochannels. Water is repelled by the PVDF but is able to move through the PEO regions, thus enhancing the overall transport through the commercial PVDF membrane. The PEO segments interact strongly with the water molecules, which prevents organics from clinging and fouling the membrane. The membranes can also be used for molecular sieving, as demonstrated by the separation of similarly charged dye molecules, and for size-exclusion chromatography, as demonstrated by the separation of vitamins B2 and B12. — MSL Macromolecules 10.1021/ma048837s (2004).