Influence of Marangoni stress on the variation in number of coalescence cascade stages

2018 ◽  
Vol 97 (4) ◽  
pp. 983-994 ◽  
Author(s):  
Krishnayan Haldar ◽  
Samarshi Chakraborty ◽  
Sudipto Chakraborty
Keyword(s):  
Marangoni Stress

scholarly journals A model of bubble coalescence in the presence of a nonionic surfactant with a low bubble approach velocity

2021 ◽  
Author(s):  
Yuelin Wang ◽  
Huahai Zhang ◽  
Tiefeng Wang
Keyword(s):  
Nonionic Surfactant ◽  
Surfactant Concentration ◽  
Bubble Coalescence ◽  
Bulk Concentration ◽  
High Concentration ◽  
Coalescence Time ◽  
Approach Velocity ◽  
Marangoni Stress ◽  
High Concentrations ◽  
High Concentration Range

A bubble coalescence model for a solution with a nonionic surfactant and with a small bubble approach velocity was developed, in which the mechanism of how coalescence is hindered by Marangoni stress was quantitatively analyzed. The bubble coalescence time calculated for ethanol-water and MIBC-water systems were in good agreement with experimental data. At low surfactant concentrations, the Marangoni stress and bubble coalescence time increased with bulk concentration increase. Conversely, in the high concentration range, the Marangoni stress and coalescence time decreased with bulk concentration. Numerical results showed that the nonlinear relationship between coalescence time and surfactant concentration is determined by the mass transport flux between the film and its interface, which tends to diminish the spatial concentration variation of the interface, i.e., it acts as a “damper”. This damping effect increases with increased surfactant concentration, therefore decreasing the coalescence time at high concentrations.

scholarly journals Sedimentation of a surfactant-laden drop under the influence of an electric field

2018 ◽  
Vol 849 ◽  
pp. 277-311 ◽  
Author(s):  
Antarip Poddar ◽  
Shubhadeep Mandal ◽  
Aditya Bandopadhyay ◽  
Suman Chakraborty
Keyword(s):  
Surface Tension ◽  
Electric Field ◽  
Surfactant Concentration ◽  
Perturbation Technique ◽  
Internal Flow ◽  
Dielectric Fluid ◽  
Regular Perturbation ◽  
Spherical Drop ◽  
Leaky Dielectric ◽  
Marangoni Stress

The sedimentation of a surfactant-laden deformable viscous drop acted upon by an electric field is considered theoretically. The convection of surfactants in conjunction with the combined effect of electrohydrodynamic flow and sedimentation leads to a locally varying surface tension, which subsequently alters the drop dynamics via the interplay of Marangoni, Maxwell and hydrodynamic stresses. Assuming small capillary number and small electric Reynolds number, we employ a regular perturbation technique to solve the coupled system of governing equations. It is shown that when a leaky dielectric drop is sedimenting in another leaky dielectric fluid, the Marangoni stress can oppose the electrohydrodynamic motion severely, thereby causing corresponding changes in the internal flow pattern. Such effects further result in retardation of the drop settling velocity, which would have otherwise increased due to the influence of charge convection. For non-spherical drop shapes, the effect of Marangoni stress is overcome by the ‘tip-stretching’ effect on the flow field. As a result, the drop deformation gets intensified with an increase in sensitivity of the surface tension to the local surfactant concentration. Consequently, for an oblate type of deformation the elevated drag force causes a further reduction in velocity. For similar reasons, prolate drops experience less drag and settle faster than the surfactant-free case. In addition to this, with increased sensitivity of the interfacial tension to the surfactant concentration, the asymmetric deformation about the equator gets suppressed. These findings may turn out to be of fundamental significance towards designing electrohydrodynamically actuated droplet-based microfluidic systems that are intrinsically tunable by varying the surfactant concentration.

scholarly journals Axisymmetric spreading of surfactant from a point source

2017 ◽  
Vol 832 ◽  
pp. 777-792 ◽  
Author(s):  
Shreyas Mandre
Keyword(s):  
Fluid Velocity ◽  
Radial Distance ◽  
Domain Size ◽  
Fluid Interface ◽  
Viscous Forces ◽  
Constant Rate ◽  
Adsorbed Phase ◽  
Self Similar ◽  
Marangoni Stress ◽  
Dissolved Phase

Guided by computation, we theoretically calculate the steady flow driven by the Marangoni stress due to a surfactant introduced on a fluid interface at a constant rate. Two separate extreme cases, where the surfactant dynamics is dominated by the adsorbed phase or the dissolved phase, are considered. We focus on the case where the size of the surfactant source is much smaller than the size of the fluid domain, and the resulting Marangoni stress overwhelms the viscous forces so that the flow is strongest in a boundary layer close to the interface. We derive the resulting flow in a region much larger than the surfactant source but smaller than the domain size by approximating it with a self-similar profile. The radially outward component of fluid velocity decays with the radial distance $r$ as $r^{-3/5}$ when the surfactant spreads in an adsorbed phase, and as $r^{-1}$ when it spreads in a dissolved phase. Universal flow profiles that are independent of the system parameters emerge in both the cases. Three hydrodynamic signatures are identified to distinguish between the two cases and verify the applicability of our analysis with successive stringent tests.

scholarly journals Self-Propulsion of Pure Water Droplets by Spontaneous Marangoni-Stress-Driven Motion

2014 ◽  
Vol 113 (24) ◽  
Author(s):  
Ziane Izri ◽  
Marjolein N. van der Linden ◽  
Sébastien Michelin ◽  
Olivier Dauchot
Keyword(s):  
Pure Water ◽  
Water Droplets ◽  
Marangoni Stress
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