Abstract

Osmosis describes the flow of water across semipermeable membranes powered by the chemical free energy contained in salinity gradients. It is a fundamental transport process for water in all living systems, and its applications are countless. While osmosis can be expressed fundamentally in simple terms via the van’t Hoff ideal gas formula for the osmotic pressure, it is a subtle phenomenon taking its roots in the interactions occurring at the scale of the membrane nanopores.

In this talk, I will discuss some molecular views of osmosis, which will be used in various contexts in order to harvest this powerful transport phenomenon. I will first discuss how specific designs of nanochannels leads to rectification of transport. In particular I will show that beyond ionic diode effects, one may obtain a rectification of the water transport, ie of the osmotic pressure. This osmotic diode opens new opportunities for water purification and complex flow control in nanochannels. I will then discuss the phenomenon of diffusio-osmosis, which is an interfacially driven transport phenomenon allowing for osmotic flow without the need of semi-permeable membranes. Beyond the theoretical descirption of the phenomenon, I will illustrate these concepts on the basis of various experiments, in particular using individual boron-nitride and carbon nanotubes, as well as nanochannels. Finally, applications to osmotic energy harvesting will be discussed.

1. « Nanofluidic osmotic diodes », C. Picallo, S. Gravelle, L. Joly, E. Charlaix and L. Bocquet, Physical Review Letters 111 244501 (2013)
2. « Giant osmotic energy conversion measured in a single transmembrane boron-nitride nanotube », A. Siria, P. Poncharal, A.-L. Biance, R. Fulcrand, X. Blase, S. Purcell, and L. Bocquet, Nature 494, 455-458 (2013)
3. « Osmotic flows through fully permeable nano-channels », C. Lee, C. Cottin, A.-L. Biance, P. Joseph, L. Bocquet, and C. Ybert, Physical Review Letters 112, 244501 (2014)