ESPCI web site
Osmotic flows, from nanoscales to kidney filtration
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
explore in particular the phenomenon of diffusio-osmosis, which is an interfacially
driven transport phenomenon allowing for osmotic flow without the need of
semi-permeable membranes. I will illustrate these concepts on the basis of various
experiments using individual nanopores and nanotubes made of carbon and
boron-nitride materials. Applications to osmotic energy harvesting will be
highlighted.
Finally I will discuss the kidney filtration process. I will show in particular that
the central piece of the kidney filtration, the U-shaped loop of Henle, is designed
as an active osmotic exchanger. This counter-intuitive and efficient separation
process is shown to operate at a remarkably small energy cost, typically one order
of magnitude smaller than traditional sieving processes like nanofiltration. This
suggests the design of a bio-inspired ”kidney on a chip” mimicking the kidney
filtration process.
Laboratoire de Physique Statistique
Ecole Normale Supérieure and CNRS
http://www.phys.ens.fr/ lbocquet
