Nonlinear Viscous Water at Nanoporous Two-Dimensional Interfaces Resists High-Speed Flow through Cooperativity.

Recently emerging ultrathin two-dimensional carbon materials provide potentially game-changing membranes for water filtration. Here we discover a changed water behavior at the nanoscale that is significantly distinct from its bulk state as water flows through two-dimensional carbon allotropes. We find that water exhibits a very high viscosity due to the cooperativity of water molecules that enhances the nonbonded H-bond interactions with the dense lattice of carbon structures, which renders flow significantly more viscous, with a resistance that is inversely proportional to the sixth power of the characteristic length of the nanopores. This is in contrast to a constant value as assumed in conventional knowledge. Our findings reveal how water molecules behave drastically different from their bulk state under extreme nanoconfinement conditions. These insights enable us to incorporate the size analysis of particles in variant untreated water into membrane design and propose the design of more efficient devices with higher filtration throughput and greater mechanical resilience.