An analytical model for transport capacity of water confined in nanopores

Abstract

Currently, a key scientific question has been urgently raised up by nanoscale associated industry that how to generate precise prediction results of transport capacity for nanoconfined water. The proper solution for the aforementioned issue will directly contribute to the development as well as economic interests of the related industry. Notably, unlike well-established theory for water transport through conventional pore scale, flow behavior of nanoconfined water remains unclear nowadays to a large extent resulting from the varying intermolecular interactions between water and pore surface. The interplay between water molecules and pore surface has tremendous effects on near-wall water physical properties, including viscosity, density as well as the boundary condition. These effects can be reasonably overlooked at the macroscopic scale, however, play crucial roles when it comes to nanoscale and should be properly treated. Herein, a novel model is developed to characterize water transport capacity within nanopores, in which above physical properties of nanoconfined water are related to surface wettability explicitly representing water-wall interactions. Meanwhile, apparent permeability, a concept from the petroleum industry is employed here to describe the transport capacity of nanoconfined water. Results show that (a) effect of surface wettability will become stronger within smaller pore dimension and enhance factor will increase with the increase of contact angle at a certain pore radius as a result from the stronger water slip phenomenon; (b) Due to the weak effect of surface wettability on nanoconfined water transport capacity at large pore size, enhance factor will close to one with the increase of pore size. (c) Through analyzing effect of critical thickness of the interfacial region, it can be demonstrated that the proposed model can be applied to the majority of pore surface of contact angle larger than 100° with high accuracy. Moreover, utmost caution should be paid when using the proposed model to pore surface with contact angle is relatively small (<40°). Finally, it is necessary to mention that the proposed model possesses analytically formulas, which greatly facilitate predicting nanoconfined water flow performance under various conditions. The above feature of the proposed model presents broad application potential in the related industry, like water purification, energy storage, and geophysical processes.