Rate effects on layering of a confined linear alkane

TL;DR

This study investigates how the rate of confinement affects molecular layering and viscosity in thin films of n-hexadecane, revealing that high shear rates can induce metastable disordered states in the film.

Contribution

It demonstrates the significant influence of confinement rate on molecular layering and viscosity in confined alkane films, highlighting the formation of metastable states at high shear rates.

Findings

Molecular layering is suppressed at high shear rates.

Confined films exhibit increased viscosity below 10 nm thickness.

Rapid confinement can produce metastable disordered states.

Abstract

We perform drainage experiments of a linear alkane fluid (n-hexadecane) down to molecular thicknesses, and focus on the role played by the confinement rate. We show that molecular layering is strongly influenced by the velocity at which the confining walls are approached: under high enough shear rates, the confined medium behaves as a structureless liquid of enhanced viscosity for film thickness below $\sim$10 nm. Our results also lead us to conclude that a rapidly confined film can be quenched in a metastable disordered state, which might be related with recent intriguing results on the shear properties of confined films produced at different rates [Zhu and Granick, Phys. Rev. Lett. {\bf 93}, 096101 (2004)].