Capillary filling with giant liquid/solid slip: dynamics of water uptake by carbon nanotubes

TL;DR

This paper revises the classical capillary filling theory for nanometric pores with large liquid/solid slip, showing that flow dynamics are dominated by wall friction and that early filling stages require considering entrance effects, especially in carbon nanotubes.

Contribution

It introduces a modified model for capillary filling accounting for giant slip lengths, highlighting the dominance of wall friction and the limitations of classical theory at early stages.

Findings

Flow is controlled by wall friction, not viscosity.

Filling velocity is independent of tube radius in the slip regime.

Entrance effects are significant in early water filling of carbon nanotubes.

Abstract

This article discusses the way the standard description of capillary filling dynamics has to be modified to account for liquid/solid slip in nanometric pores. It focuses in particular on the case of a large slip length compared to the pore size. It is shown that the liquid viscosity does not play a role, and that the flow is only controlled by the friction coefficient of the liquid at the wall. Moreover in the Washburn regime, the filling velocity does not depend on the tube radius. Finally, molecular dynamics simulations suggest that this standard description fails to describe the early stage of capillary filling of carbon nanotubes by water, since viscous dissipation at the tube entrance must be taken into account.