Multiscale simulation of enhanced water flow in nanotubes of different materials

Nanotubes (NTs) with diameters less than 2 nm have been proposed for next-generation reverse osmosis membranes. At this molecular scale, the NTs are narrow enough to block salt ions and other contaminants, but still wide enough to allow water to flow along the NTs at seemingly unprecedented rates. Simulations for design of NT membranes can be challenging. On the one hand, the standard equations for water flow through pipes are not applicable at sub-2-nm scales due to the dominance of non-continuum phenomena; on the other hand, full molecular simulations are computationally intractable for flows up to laboratory or prototype scales. This article describes recent multiscale approaches to simulating flows through aligned NT membranes of various materials. These multiscale techniques offer a unique and economical solution that can shed light on sometimes conflicting experimental results and point the way to future engineering design of nanostructured membranes.