TY  - JOUR
N2  - In this work the coalescence of an aqueous drop with a flat aqueous-organic interface was investigated in a thin gap Hele-Shaw cell. Different concentrations of a nonionic surfactant (Span 80) dissolved in the organic phase were studied. We present experimental results on the velocity field inside a coalescing droplet in the presence of surfactants. The evolution of the neck between the drop and the interface was studied with high-speed imaging. It was found that the time evolution of the neck at the initial stages of coalescence follows a linear trend, which suggests that the local surfactant concentration at the neck region for this stage of coalescence can be considered quasiconstant in time. This neck expansion can be described by the linear law developed for pure systems when the surfactant concentration at the neck is assumed higher than in the bulk solution. In addition, velocity and vorticity fields were computed inside the coalescing droplet and the bulk homophase using a high-speed shadowgraphy technique. The significant wall effects in the Hele-Shaw cell in the transverse axis cause the two vertical velocity components towards the singularity rupture point, from the drop and from the bulk homophase, to be of the same order of magnitude. This movement together with the neck expansion creates two pairs of counteracting vortices in the drop and in the bulk phase. The neck velocity is the average of the advection velocities of the two counteracting vortex pairs on each side of the neck. The presence of the surfactant slows down the dynamics of the coalescence, affects the propagation direction of the pair of vortices in the bulk phase, and reduces their size faster compared to the system without surfactant.
ID  - discovery1520066
UR  - http://dx.doi.org/10.1103/PhysRevE.94.033101
PB  - AMER PHYSICAL SOC
SN  - 2470-0045
JF  - Physical Review E
A1  - Chinaud, M
A1  - Voulgaropoulos, V
A1  - Angeli, P
KW  - Science & Technology
KW  -  Physical Sciences
KW  -  Physics
KW  -  Fluids & Plasmas
KW  -  Physics
KW  -  Mathematical
KW  -  Physics
KW  -  LIQUID
KW  -  ADSORPTION
KW  -  FLUID
TI  - Surfactant effects on the coalescence of a drop in a Hele-Shaw cell
AV  - public
Y1  - 2016/09/01/
VL  - 94
EP  - 11
N1  - This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article?s title, journal citation, and DOI.
ER  -