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Nanofluidics inside a single carbon nanotube

Final Report Summary - MICROMEGAS (Nanofluidics inside a single carbon nanotube)

« There is plenty of room at the bottom ». This visionary foresight of R. Feynman, introduced during a lecture at Caltech in 1959, was at the root of numerous scientific and technological developments, taking benefit of the "strange phenomena" occuring at the smallest scales. There remains however a lot to explore, in particular in the context of fluids at the nanoscales and their specific transport properties. The great efficiency of biological nanopores, such as aquaporins, in terms of permeability or selectivity is definitely a great motivation to foster research in this direction.
In this context, some measurements revealed fast water transport across carbon nanotube membranes, owing to nearly frictionless interfaces. These observations have stimulated a strong interest in nanotube-based membranes, with potential breakthroughs in ultrafiltration, desalination and energy harvesting. The results remained however controversial with conflicting results for the limited number of experimental results so far, and a lack of a satisfactory theoretical explanation in spite of numerous numerical investigations. Advancing the fundamental understanding of fluid transport at the smallest scales requires mass and ion dynamics to be ultimately characterized across an individual channel so to avoid averaging over many pores. This was the objective of the Micromegas project.
During the course of the project, we have created a new toolbox to allow for the fundamental study of transport across single nano-objects. This required to develop unconventional tools to fabricate nanofluidic devices amenable for fluid transport properties. We followed a novel nano-assembly route using nanostructures as building blocks and assembled under the beam of a electron microscope. This also required to develop new approaches to fully characterize the fluid transport properties across such individual nanotubes, under various driving forces. New methods to measure minute flow rate were accordingly invented, going far beyond the state-of-the-art in order to meet the considerable challenge of measuring flow properties of single nanotubes.
This accordingly opened a virgin territory, that I explored systematically with my team within the Micromégas projects. Among a diversity of results, the project led to two groundbreaking outcomes:
(1) massive electric currents through a Boron-Nitride nanotube were measured under salinity gradient. Boron-Nitride nanotubes thus provide an extremely efficient solution for converting the (osmotic) energy of salinity gradients into immediately usable electrical power. We have demonstrated by scaling-up results towards large scale membranes that this type of energy, the so-called osmotic power, is a future and exciting challenge to make the osmotic energy a sustainable « blue » energy source.
(2) we revealed, for the first time and unambiguously, very fast flows in carbon nanotubes, furthermore with radius-dependent friction (or slippage) in carbon nanotubes. In contrast we showed that boron nitride nanotubes that are crystallographically similar to carbon nanotubes, but electronically different, exhibit no flow enhancement. This pronounced contrast between the two systems points to subtle differences the atomic-scale details of their solid–liquid interfaces, illustrating that nanofluidics is the frontier at which the continuum picture of fluid mechanics meets the atomic nature of matter.
This opens up a new avenue for research that could bridge the gap between condensed matter physics and fluid dynamics.