Molecular fluid mechanics - A field of innovation for water and energy

Illustration lecture Lydéric Bocquet 2022-2023

This lecture describes the latest advances in the emerging field of nanofluidics, the science of molecular flows, which explores fluid flow and transport at nanometric scales. This world of infinitely small fluidics is the frontier where the continuum of fluid mechanics meets the atomic nature of matter, or even its quantum nature. This is the frontier where the continuum of fluid mechanics meets the atomic nature of matter, and even its quantum nature. We can observe virtually frictionless flows, emerging quantum effects, and memory effects that now make it possible to dream of ionic calculators. Nature takes full advantage of fluidic quirks at the nanoscale. Using a circuitry made up of multiple biological channels, it is capable of incredible technological feats : ion pumps, proton turbines, ultra-selective pores, stimulable channels... simply breathtaking fluidic goldsmithery. Can we draw inspiration from and match these performances with artificial channels ? What are the specific properties of fluids at nanoscale ? How can they be quantified experimentally ? Can they be exploited for innovation ?

The lecture will address the fundamental questions posed by fluid transport at molecular or nanoscale, and the emerging properties at these scales. In particular, we will introduce the new experimental and theoretical tools that have been developed to measure, understand and exploit new transport properties at nano-scales. We will also discuss a number of phenomena that have recently come to light, and which, while not exhaustive, provide an insight into important advances in nanofluidics : continuum limit(s) ; role of fluctuations ; classical and quantum friction ; linear ion transport and molecular sieving ; non-linear ion transport, diodes and ion Coulomb blockade ; Bjerrum pairs, Kosterlitz-Thouless transition, Wien effect ; neuromorphic responses ; osmosis, van 't Hoff and unconventional osmosis phenomena ; etc.

Nanofluidics is also a field where there is a short path between fundamental science and disruptive innovation, as new nanofluidic properties offer unexpected solutions for multiple applications, including desalination, water remediation, or blue energy - notably osmotic energy. We will explore a few examples where this path has led to breakthrough innovations.

It's difficult to cover the whole field exhaustively, as it encompasses multiple concepts at the interface between hydrodynamics, statistical physics, non-equilibrium thermodynamics, condensed matter, chemistry and more. We will therefore approach the subject in "impressionistic " fashion, highlighting and focusing on key concepts, important experiments and recent theoretical advances. These emerging concepts are at the heart of fundamental research in nanofluidics and their link to innovation.