Pearling instability of nanoscale fluid flow confined to a chemical channel

TL;DR

This paper studies the stability of nanoscale liquid ridges in chemical channels, revealing a pearling instability that occurs when the ridge exceeds a certain thickness, with implications for fluid flow control at the nanoscale.

Contribution

It combines molecular dynamics, long-wavelength approximation, and stability analysis to understand the pearling instability in nanoscale fluid flows within chemical channels.

Findings

Thin ridges are stable during flow.

Pearling instability occurs when ridge thickness exceeds half the channel width.

Flowing ridges develop propagating bulges that merge without breaking up.

Abstract

We investigate the flow of a nano-scale incompressible ridge of low-volatility liquid along a "chemical channel": a long, straight, and completely wetting stripe embedded in a planar substrate, and sandwiched between two extended less wetting solid regions. Molecular dynamics simulations, a simple long-wavelength approximation, and a full stability analysis based on the Stokes equations are used, and give qualitatively consistent results. While thin liquid ridges are stable both statically and during flow, a (linear) pearling instability develops if the thickness of the ridge exceeds half of the width of the channel. In the flowing case periodic bulges propagate along the channel and subsequently merge due to nonlinear effects. However, the ridge does not break up even when the flow is unstable, and the qualitative behavior is unchanged even when the fluid can spill over onto a partially wetting exterior solid region.