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

Abstract

Cooling down water in its supercooled regime has been widely considered to better understand the bulk transport properties of this ubiquitous liquid. Here we apply the same approach to investigate the wall slip induced by low interfacial friction, a key factor in the performance of nanofluidic systems. Specifically, we investigated the temperature dependence of friction and slip for water and methanol on model Lennard-Jones walls and on graphene. Surprisingly, although interfacial friction and viscosity in bulk follow the same fundamental laws and are proportional at high temperatures, the relation of proportionality breaks down in the supercooled regime. This implies that wall slip, controlled by the ratio between viscosity and friction, increases in the deep supercooled regimeby up to a factor of 5 for water on graphene. Whereas most previous studies have focused on the role of static features of the interface, here we focus on the intriguing role of dynamics. We find that the interfacial density relaxation of the fluid -and how it evolves with respect to the bulk one -governs the temperature dependence of wall slip. Overall, exploring the temperature dependence of water-wall slip provides new insight on its molecular mechanisms, and can also shed light on the bulk transport properties of water.