Iterated stretching and multiple beads-on-a-string phenomena in dilute solutions of highly-extensible flexible polymers

TL;DR

This study investigates the complex dynamics of elastocapillary thinning in dilute solutions of highly-extensible flexible polymers, revealing iterated bead formation, instabilities, and coalescence phenomena through high-speed video microscopy.

Contribution

It provides new experimental insights into bead-on-a-string phenomena, including multiple generations of beads and their instability mechanisms, extending previous theoretical predictions.

Findings

Formation of multiple bead generations during thinning

Observation of instabilities propagating from bead-neck connections

Finite extensibility limits the iterated instability process

Abstract

The dynamics of elastocapillary thinning in high molecular weight polymer solutions are re-examined using high-speed digital video microscopy. At long times, the evolution of the viscoelastic thread deviates from self-similar exponential decay and competition of elastic, capillary and inertial forces leads to the formation of a periodic array of beads connected by axially-uniform ligaments. This configuration is itself unstable and successive instabilities propagate from the necks connecting the beads and ligaments. This iterated process results in the development of multiple generations of beads in agreement with predictions of Chang et al. (1999), although experiments yield a different recursion relation between successive generations. At long times, finite extensibility truncates the iterated instability and axial translation of the bead arrays along the interconnecting threads leads to progressive coalescence before rupture of the fluid column.