Fast Increase of Nanofluidic Slip in Supercooled Water: the Key Role of Dynamics

TL;DR

This study reveals that water exhibits a significant increase in slip length when supercooled below its melting point, driven by decoupling of viscosity and density relaxation, with implications for nanofluidic applications and anti-icing surfaces.

Contribution

It demonstrates the rapid increase in nanofluidic slip in supercooled water through molecular dynamics simulations, highlighting the molecular mechanisms behind this phenomenon.

Findings

Slip length increases up to five times below melting point

Decoupling of viscosity and density relaxation explains slip behavior

Potential for enhanced nanofluidic performance at low temperatures

Abstract

Nanofluidics is an emerging field offering innovative solutions for energy harvesting and desalination. The efficiency of these applications depends strongly on liquid-solid slip, arising from a favorable ratio between viscosity and interfacial friction. Using molecular dynamics simulations, we show that wall slip increases strongly when water is cooled below its melting point. For water on graphene, the slip length is multiplied by up to a factor of five and reaches $230$nm at the lowest simulated temperature, $T \sim 225$K; experiments in nanopores can reach much lower temperatures and could reveal even more drastic changes. The predicted fast increase in water slip can also be detected at supercoolings reached experimentally in bulk water, as well as in droplets flowing on anti-icing surfaces. We explain the anomalous slip behavior in the supercooled regime by a decoupling between viscosity and bulk density relaxation dynamics, and we rationalize the wall-type dependency of the enhancement in terms of interfacial density relaxation dynamics. By providing fundamental insights on the molecular mechanisms of hydrodynamic transport in both interfacial and bulk water in the supercooled regime, this study is relevant to the design of anti-icing surfaces and it also paves the way to explore new behaviors in supercooled nanofluidic systems.