# Confinements regulate capillary instabilities of fluid threads

## TL;DR

This paper investigates how confinement influences the stability and breakup of fluid threads at low flow rates, combining experiments, simulations, and analytical methods to identify critical conditions and mechanisms of capillary instabilities.

## Contribution

It introduces a comprehensive approach to understanding capillary instabilities in confined fluids, highlighting two distinct mechanisms and providing critical parameters for stability analysis.

## Key findings

- Identification of critical mean radii at neck centers
- Discovery of two distinct origins of capillary instabilities
- Analytical explanation of pressure gradients affecting breakup

## Abstract

We study the breakup of confined fluid threads at low flow rates to understand instability mechanisms. To determine the critical conditions between the earlier quasi-stable necking stage and the later unstable collapse stage, simulations and experiments are designed to operate at an extremely low flow rate. Critical mean radii at neck centres are identified by the stop-flow method for elementary microfluidic configurations. Analytical investigations reveal two distinct origins of capillary instabilities. One is the gradient of capillary pressure induced by the confinements of geometry and external flow, whereas the other is the competition between local capillary pressure and internal pressure determined by the confinements.