Differences in water and vapor transport through angstrom-scale pores in atomically thin membranes

The transport of water through nanoscale capillaries/pores plays a prominent role in biology, ionic/molecular separations, water treatment and protective applications. However, the mechanisms of water and vapor transport through nanoscale confinements remain to be fully understood. Angstrom-scale pores (similar to 2.8-6.6 A) introduced into the atomically thin graphene lattice represent ideal model systems to probe water transport at the molecular-length scale with short pores (aspect ratio similar to 1-1.9) i.e., pore diameters approach the pore length (similar to 3.4 A) at the theoretical limit of material thickness. Here, we report on orders of magnitude differences (similar to 80x) between transport of water vapor (similar to 44.2-52.4 g m(-2) day(-1) Pa-1) and liquid water (0.6-2 g m(-2) day(-1) Pa-1) through nanopores (similar to 2.8-6.6 A in diameter) in monolayer graphene and rationalize this difference via a flow resistance model in which liquid water permeation occurs near the continuum regime whereas water vapor transport occurs in the free molecular flow regime. We demonstrate centimeter-scale atomically thin graphene membranes with up to an order of magnitude higher water vapor transport rate (similar to 5.4-6.1 x 10(4) g m(-2) day(-1)) than most commercially available ultra-breathable protective materials while effectively blocking even sub-nanometer (>0.66 nm) model ions/molecules.