Dynamics of capillary coalescence and breakup: quasi-two-dimensional nematic and isotropic droplets

TL;DR

This study reveals new coalescence dynamics in nematic and isotropic droplets, showing simultaneous existence of droplet and outer bridges, leading to satellite droplet formation, which advances understanding of fluid breakup processes.

Contribution

It demonstrates for the first time that both droplet and outer bridges can coexist during coalescence, fundamentally changing the understanding of droplet coalescence and breakup.

Findings

Coexistence of droplet and outer bridges during coalescence.

Formation of satellite droplets from the bridge breakup.

Connection of coalescence and breakup processes in fluid dynamics.

Abstract

For the first time we observed formation of small satellite droplets from the bridge at droplet coalescence. Investigations were made using a Hele-Shaw cell in the two-phase region at nematic-isotropic phase transition. In previous works on coalescence it was considered that before start of coalescence there exists a bridge between the outer fluid connecting regions on the two sides of the droplets (outer bridge). After start of coalescence a bridge connecting the two droplets appears (droplet bridge) and the outer bridge is broken. For the first time we have shown that there are coalescence processes when after start of coalescence both the droplet bridge and the outer bridge can exist. This cardinally changes the coalescence process. During the first coalescence stage the size of the outer bridge decreases, the size of the droplet bridge increases. During the second stage the outer bridge becomes unstable with pinch-off, formation of pointed end domains, secondary instability, splitting of pointed end domains and formation of satellite droplets. Our work connects two areas of fluid dynamics: coalescence and breakup with formation of satellite droplets.