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

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics. 2021. Vol. 104. No. 1. Article 014702.

P.V. Dolganov, Zverev A. S., K.D. Baklanova, Dolganov V. K.

We observed the 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 the nematic-isotropic phase transition. In
previous works on coalescence it was considered that before the start of
coalescence there exists a bridge between the outer fluid connecting
regions on the two sides of the droplets (outer bridge). After the start
of coalescence, a bridge connecting the two droplets appears (droplet
bridge) and the outer bridge is broken. We have shown that there are
coalescence processes where after the 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 and the size of the droplet bridge increases.
During the second stage the outer bridge becomes unstable which leads to
pinch-off, formation of pointed end domains, secondary instability,
splitting of pointed end domains, and formation of satellite droplets.
We found the linear dependence of the minimum bridge radius on time near
bridge breakup. This behavior confirms the capillary viscous regime of
bridge breakup. Our work connects two areas of fluid dynamics:
coalescence and breakup with formation of satellite droplets.

Keywords: liquid crystals, Drop coalescence, Drop breakup