The study investigates the permeation properties of submicron-thick graphene oxide (GO) membranes, which are impermeable to liquids, vapors, and gases but allow unimpeded water permeation. The researchers attribute this seemingly contradictory behavior to the nearly frictionless flow of a monolayer of water through two-dimensional capillaries formed by closely spaced graphene sheets. Other molecules are blocked by the water that clogs the capillaries and their reversible narrowing in low humidity. Despite being only one atom thick, graphene is believed to be impermeable to all gases and liquids, making it a promising material for barrier films. The GO membranes, made from graphene oxide, exhibit a high gas barrier, with a permeability rate for helium (He) of approximately \(10^{-15} \, \text{mm} \, \text{g/cm}^2 \, \text{s} \, \text{bar}\). For liquids, the GO membranes show a significant weight loss for water, indicating unimpeded evaporation, while other liquids like ethanol and hexane exhibit no detectable permeation. The permeation of water is limited by evaporation from the wetted surface of the GO, and the mechanism involves a monolayer of water molecules moving through the capillaries with high velocities, sustained by a capillary-like pressure. This phenomenon has implications for various applications, such as filtration and separation, and explains why the observed surface areas of GO-based materials are close to the theoretical maximum.The study investigates the permeation properties of submicron-thick graphene oxide (GO) membranes, which are impermeable to liquids, vapors, and gases but allow unimpeded water permeation. The researchers attribute this seemingly contradictory behavior to the nearly frictionless flow of a monolayer of water through two-dimensional capillaries formed by closely spaced graphene sheets. Other molecules are blocked by the water that clogs the capillaries and their reversible narrowing in low humidity. Despite being only one atom thick, graphene is believed to be impermeable to all gases and liquids, making it a promising material for barrier films. The GO membranes, made from graphene oxide, exhibit a high gas barrier, with a permeability rate for helium (He) of approximately \(10^{-15} \, \text{mm} \, \text{g/cm}^2 \, \text{s} \, \text{bar}\). For liquids, the GO membranes show a significant weight loss for water, indicating unimpeded evaporation, while other liquids like ethanol and hexane exhibit no detectable permeation. The permeation of water is limited by evaporation from the wetted surface of the GO, and the mechanism involves a monolayer of water molecules moving through the capillaries with high velocities, sustained by a capillary-like pressure. This phenomenon has implications for various applications, such as filtration and separation, and explains why the observed surface areas of GO-based materials are close to the theoretical maximum.