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

Abstract

For the first time we observed Rayleigh-Plateau instability with formation of satellite domains at droplet coalescence. Investigations were made using a Hele-Shaw cell in the twophase region at nematic-isotropic phase transition. In previous works on quasi-2D 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 the outer bridge continues to 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 domains. Our work connects two directions of fluid dynamics: coalescence and breakup related with Rayleigh-Plateau instability.

A Review on the Coalescence of Confined Drops with a Focus on Scaling Laws for the Growth of the Liquid Bridge

“…Copyright 2011 by National Academy of Sciences. Dolganov et al observed the same power-law scaling relation (r~t 1/4 ) as Yokota and Okumura for the coalescence of two drops of liquid crystal E7 occurring in a Hele-Shaw cell (D = 5-50 µm)[41]. In their study, coalescence occurred between two quasi-2D drops, not between a drop and a bath.…”

“…Chinaud et al observed that the bridge grew linearly with time (i.e., r~t) irrespective [41]. In their study, coalescence occurred between two quasi-2D drops, not between a drop and a bath.…”

“…It is noticeable in Figure 16c that the scaling law for the later time regime resulted in a good superposition of data sets, even for the early time regime. [41]. In their study, coalescence occurred between two quasi-2D drops, not between a drop and a bath.…”

The Dark Annulus of a Drop in a Hele-Shaw Cell Is Caused by the Refraction of Light through Its Meniscus

“…The round, or even circular, meniscus profile was expected because of the small gap height of the Hele-Shaw cell (i.e., Bo < 1). Similarly, Dolganov et al found that the cross-sectional meniscus profile of a liquid crystal drop in a Hele-Shaw cell was close to circular [ 23 , 24 ].…”

Coalescence of biphasic droplets embedded in free standing smectic A films

“…It is interesting to compare our experiment with the coalescence of isotropic droplets separated by a nematic bridge of the same material in flat cells. This scenario was studied by Dolganov et al 93,94 The situation is different there because the experiments were performed in Hele-Shaw cells. The presence of the upper and lower glass plates changes the situation completely.…”