Dynamic Interfacial Tension of Surfactant Mixtures at Liquid–Liquid Interfaces

Campanelli, J. R.; Wang, Xiaohong

doi:10.1006/jcis.1999.6149

Cited by 58 publications

(42 citation statements)

References 12 publications

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“…Span 80 (0.05% in volume, Sigma-Aldrich, USA) is dissolved in hexadecane, which reduces the hexadecane/water surface tension from 50 mN/m to 10 mN/m, as measured using the pendant droplet method (Theta tensiometers, Attension, Finland). According to Campanelli and Wang,32 the concentration of the surfactant is below the critical micelle concentration (CMC). Hexadecane and water are introduced into the channel using three syringe pumps (Pump 11 Elite, Harvard Apparatus Inc., USA).…”

Section: Methodsmentioning

confidence: 99%

Inertial migration of deformable droplets in a microchannel

Chen

Xue

Zhang³

et al. 2014

Physics of Fluids

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The microfluidic inertial effect is an effective way of focusing and sorting droplets suspended in a carrier fluid in microchannels. To understand the flow dynamics of microscale droplet migration, we conduct numerical simulations on the droplet motion and deformation in a straight microchannel. The results are compared with preliminary experiments and theoretical analysis. In contrast to most existing literature, the present simulations are three-dimensional and full length in the streamwise direction and consider the confinement effects for a rectangular cross section. To thoroughly examine the effect of the velocity distribution, the release positions of single droplets are varied in a quarter of the channel cross section based on the geometrical symmetries. The migration dynamics and equilibrium positions of the droplets are obtained for different fluid velocities and droplet sizes. Droplets with diameters larger than half of the channel height migrate to the centerline in the height direction and two equilibrium positions are observed between the centerline and the wall in the width direction. In addition to the well-known Segré-Silberberg equilibrium positions, new equilibrium positions closer to the centerline are observed. This finding is validated by preliminary experiments that are designed to introduce droplets at different initial lateral positions. Small droplets also migrate to two equilibrium positions in the quarter of the channel cross section, but the coordinates in the width direction are between the centerline and the wall. The equilibrium positions move toward the centerlines with increasing Reynolds number due to increasing deformations of the droplets. The distributions of the lift forces, angular velocities, and the deformation parameters of droplets along the two confinement direction are investigated in detail. Comparisons are made with theoretical predictions to determine the fundamentals of droplet migration in microchannels. In addition, existence of the inner equilibrium position is linked to the quartic velocity distribution in the width direction through a simple model for the slip angular velocities of droplets.

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Section: Methodsmentioning

confidence: 99%

Inertial migration of deformable droplets in a microchannel

Chen

Xue

Zhang³

et al. 2014

Physics of Fluids

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“…A pendant drop of 100 µL ultra pure water is emitted at the tip of a vertical cylindrical pipette which is immersed in a thermostated oil bath. After an equilibration delay of 3 minutes, 15 the interfacial tension γ is obtained from the drop shape, 16 taking into account the temperature dependence of the liquid densities. 17 The temperature dependence of surface tension is measured by increasing the temperature of the oil bath from 23 to 60°C, for a bulk surfactant concentration equivalent to the microfluidics experiments C=36 mol.m −3 (2 wt%).…”

Section: Surface Tension At Equilibriummentioning

confidence: 99%

“…These measurements are consistent with published values. 15 We use the Gibbs adsorption equation to describe the equilibrium behavior of Span 80 at the water/hexadecane interface for concentrations below the cmc, dγ = −RT Γd lnC (1) and a Langmuir isotherm…”

Section: Surface Tension At Equilibriummentioning

confidence: 99%

Laser-Induced Force on a Microfluidic Drop: Origin and Magnitude

Verneuil

Cordero

Gallaire³

et al. 2009

Langmuir

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The localized heating produced by a tightly focused infrared laser leads to surface tension gradients at the interface of microfluidic drops covered with surfactants, resulting in a net force on the drop whose origin and magnitude are the focus of this paper. First, by colocalization of the surfactant micelles with a fluorescent dye, we demonstrate that the heating alters their spatial distribution, driving the interface out of equilibrium. This soluto-capillary effect opposes and overcomes the purely thermal dependence of the surface tension, leading to reversed interfacial flows. As the surface of the drop is set into motion, recirculation rolls are created outside and inside the drop that we measure using time-resolved micro-Particle Image Velocimetry. Second, the net force produced on the drop is measured using an original microfluidic design. For a drop 300 µm-long and 100 µm wide we obtain a force of 180 † Laboratoire d'Hydrodynamique (LadHyX), Ecole Polytechnique, 91128 Palaiseau, France ‡ Laboratoire J.A. Dieudonné, Université de Nice Sophia-Antipolis, 06108 Nice, France § Current address:Department of Physics, University of Pennsylvania, Philadelphia, PA 1 Emilie Verneuil et al.Laser-induced force on a drop nN for a laser power of 100 mW. This micro-dynanometer further shows that the magnitude of the heating, which is determined by the laser power and its absorption in the water, sets the magnitude of the net force on the drop. On the other hand, the dynamics of the force generation is limited by the time scale for heating which has independently been measured to be τ Θ = 4 ms. This time scale sets the maximum velocity that the drops can have and still be blocked, by requiring that the interface passes the laser spot in a time longer than τ Θ . The maximum velocity is measured at U max = 0.7 mm/s for our geometric conditions. Finally, a scaling model is derived that describes the blocking force in a confined geometry as the result of the viscous stresses produced by the shear between the drop and the lateral walls.

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“…The use of DVT to study adsorption kinetics in this way is well established. 30,32,33 Changing flow rate within a DVT experiment is equivalent to changing the surface expansion rate, the latter being a more universal/fundamental parameter. At high expansion rates, the tension is equal to that of the surfactant-free system because the surfactant does not have time to diffuse/adsorb to the interface.…”

Section: Drop Volume Theorymentioning

confidence: 99%

“…30 A dispersed phase is dripped into a continuous phase using a needle of known diameter. If the dispersed phase is less dense than the continuous phase (as in this work), it is injected vertically upwards, e.g., using a U-shaped needle.…”

Section: Drop Volume Theorymentioning

confidence: 99%

Measurement of Dynamic Interfacial Tension in a Carbohydrate Melt at High Temperature Using a Drop Volume Tensiometer

et al. 2010

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Many food and encapsulation products are dispersed systems with a highly viscous concentrated carbohydrate solution or melt as the continuous phase and for which interfacial properties are important at high temperatures. A drop volume interfacial tensiometer was utilized to provide objective characterization of surfactant behavior in such systems at temperatures typical of food production processes. Interfacial tension was measured over a range of flow rates within a maltodextrin-sucrose-water melt at 105°C using limonene as the oil phase and a sucrose ester surfactant. The results showed that the kinetics of surfactant adsorption were faster when the surfactant was dissolved in the oil phase. However, the low critical micelle concentration in the oil phase resulted in a lower than expected diffusion coefficient.

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Dynamic Interfacial Tension of Surfactant Mixtures at Liquid–Liquid Interfaces

Cited by 58 publications

References 12 publications

Inertial migration of deformable droplets in a microchannel

Inertial migration of deformable droplets in a microchannel

Laser-Induced Force on a Microfluidic Drop: Origin and Magnitude

Measurement of Dynamic Interfacial Tension in a Carbohydrate Melt at High Temperature Using a Drop Volume Tensiometer

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