Coalescence of viscous liquid drops

Abstract

We report on studies of the early stage of coalescence of two liquid drops. The drops were high viscosity silicon oil immersed in a water-alcohol mixture of the same density in order to eliminate the effects of gravity. The viscosity was sufficiently large that measurements could be made under the conditions of Stokes flow. Measurements were made of the radius of the neck between the drops as a function of the time from the onset of coalescence, and the results compared with theoretical predictions.

Hydrodynamics of Droplet Coalescence

“…The latter has recently been observed in other experiments [7,8]. We achieve in observing the linear dependence not only by increasing the viscosity considerably as, for example, very recently shown in [9,10], but also by decreasing the surface tension by 5 orders of magnitude. To this end, we use a molecular system with a variable (high) viscosity and a colloid-polymer mixture with an ultralow surface tension [11,12].…”

Comment on “Viscous coalescence of droplets: A lattice Boltzmann study” [Phys. Fluids 25, 052101 (2013)]

“…[2][3][4][5] However, our results obtained for coalescence in a saturated vapor follow r(t)/R 0 ∼ (t/t v ) 1/2 , which is similar to the results observed by GSRV. However, our expansion speed was notably faster than what they observed.…”

“…The authors stated that the reason for these discrepancies is unknown and offered no explanation for the deviation of their results from the linear time evolution of the bridge radius r(t)/R 0 ∼ t/t v reported in experiments. [2][3][4][5] Here we comment on why the results observed by GSRV do not reproduce experimental results.…”

The interface in demixed colloid–polymer systems: wetting, waves and droplets

“…It is therefore very unlikely that this square root regime will be reached. To the contrary, the first -linear-regime of viscous coalescence is very hard to observe for molecular fluids, since the initial velocities are huge (70 m/s) and only by increasing the viscosity drastically and using ultrafast cameras the initial regime is now observed in molecular fluids as well [171,184]. Here, however, we explore the option of using a system with an ultralow interfacial tension [184].…”

“…Recently, significant theoretical [169] and numerical [170] progress has been made in the description of the neck growth, step (iii), and in understanding the singularity that occurs during coalescence. Very recently, experiments have observed the initial viscous coalescence [171], as well as the inertial coalescence [172,173], which follows the viscous coalescence.…”