Anomalous effects of water flow through charged nanochannel membranes

Abstract

A nanoscale understanding of water transport is crucial to gaining fundamental insights into biological systems and improving the design of engineered systems. Herein, anomalous effects of water flow were observed in our experiment by measuring the net flux of water through charged nanochannel membranes that separated pure water from an electrolyte solution. The direction and flux of water transport can be controlled as a function of nanochannel surface charge, electrolyte concentration and electrolyte type. For some electrolyte types in the proper concentration range, the net flux of water transport was from the electrolyte solution to the pure water, which is an anomalous osmosis phenomenon and violates van't Hoff's law. In order to explain this anomalous effect, a concise model was put forward. According to the model, the direction and flux of water transport were the result of combining concentration diffusion with induced electroosmosis under certain electrolyte gradients. In addition, neutral molecule transport, and ionic species separation through charged nanochannel membranes can also be modulated by adjusting the electrolyte gradient. These results suggest that polyelectrolyte modified nanochannel membranes have good potential for application as a kind of nanovalve under an electrolyte gradient.