From supercooled liquids to ultrastable glasses: a molecular view on confined and bulk liquids at low temperature - Cecilia Herrero (Lab. Charles Coulomb, Montpellier)

Nanofluidics, the study of fluid transport at nanometer scale, is an emerging field offering innovative solutions to desalinate water, and to harvest energy or waste heat. At the nanoscale, surface effects become crucial: in particular liquid-solid slip, arising from a favorable ratio between viscosity and interfacial friction, can boost the performance of nanofluidic devices. In this seminar, I will show how molecular dynamics simulations can help us to unravel the molecular processes occurring at the nanoscale, starting from fundamental questions up to practical and promising applications. For instance, I will show that wall slip increases strongly, up to 230 nm, when water is cooled down below its melting point, and investigate the origin of this unexpected effect.
Aside of interfacial properties, the behavior of bulk liquids at low temperatures still opens a number of theoretical and experimental challenges, such as understanding how equilibrium is achieved for ultrastable glasses and liquids with high kinetic stability. In the second part of my talk, I will discuss the molecular insights obtained into the equilibration process when temperature is rapidly increased from an ultrastable supercooled liquid. Thanks to the molecular insights provided by simulations, I will show that devitrification is a two-step process, consisting in nucleated liquid droplets that first grow very slowly at the expense of the stiff amorphous matrix. As time advances, the droplets merge into fronts that grow faster. Therefore, I will present a close analogy between devitrification and crystal melting, with important consequences for understanding the glass transition.

Contact: Benoit Coasne