Surfactant Adsorption to Spherical Particles: The Intrinsic Length Scale Governing the Shift From Diffusion to Kinetic-Controlled Mass Transfer

The bulk properties and structural characteristics of emulsions arise substantially from their interfacial rheology, which depends strongly on surfactant mass transfer and its coupling to flow. Typical methods used to measure such properties often employ simpler flows and larger drops than those encountered in typical processing applications. Mass transfer mechanisms are governed by droplet size; therefore experimentation at length scales typical of those encountered in applications is desired. Utilizing a microfluidic approach allows high-throughput experimentation at relevant length scales and with adjustable flow dynamics. Using a microfluidic device that facilitates the measurement of interfacial tension in two-phase droplet flows, particle tracers are also used to determine the droplet internal circulation velocity as a measure of interfacial mobility. Combining these measurements in a single device, the coupling between interfacial tension, interfacial retardation, and surfactant mass transfer is explored and mass transfer coefficients and interfacial mobility are measured for a two-phase system containing a diffusing surfactant. Such a device is also used to probe the deformability of elastic capsules and viscoelastic biological cells.

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“…As a guide to which of these processes is rate limiting, Jin et al [ 12 ] identifi ed in 2004 an intrinsic length scale…”

Section: Need For Interfacial Rheology At a Small Scalementioning

confidence: 99%

Interfacial Rheology Through Microfluidics

et al. 2010

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“…[37][38][39] Thus these surfactants are good candidates for study of surfactant-mediated tipstreaming in microfluidic devices, enabling a systematic investigation of the role of different mass transfer mechanisms in the process. A wide variation in surfactant solution properties such as critical micelle concentration, equilibrium surface tension, and equilibrium constants, which contain adsorption and desorption coefficients, can be achieved by adjusting the lengths of the ethoxylated head groups and carbon tail groups while maintaining the same general chemistry of the surfactant molecule.…”

Section: -3mentioning

confidence: 99%

Microscale tipstreaming in a microfluidic flow focusing device

2006

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A microfluidic flow-focusing device is used to explore the use of surfactant-mediated tipstreaming to synthesize micrometer-scale and smaller droplets. By controlling the surfactant bulk concentration of a soluble nonionic surfactant in the neighborhood of the critical micelle concentration, along with the capillary number and the ratio of the internal and external flow rates, we observe several distinct modes of droplet breakup. For the most part, droplet breakup in microfluidic devices results in highly monodisperse droplets in the range of tens of micrometers in size. However, we observe a new mode of breakup called "thread formation" that resembles tipstreaming and yields tiny droplets in the range of a few micrometers in size or smaller. In this work, we characterize the growth of the thread and its maximum length as a function of flow variables and surfactant content, and we also characterize the period of droplet breakup as a function of these variables. Our results suggest possible methods for controlling the process. Using a simple flow visualization experiment as the basis, we report on preliminary efforts to model the thread formation process.

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“…(4) can be reformulated for cylindrical or spherical coordinate systems [2]; however, the process is usually not necessary as the diffusion penetration depth l D ∼ (πDt) 1/2 is usually much smaller than the radius of curvature. However, this assumption may fail for droplets of small diameter (<70 μm) with low concentrations of surfactant, as the diffusion boundary layer will approach the size of the droplet [42]. Under such conditions, the following derivations need to be modified to account for kinetic controlled adsorption [2,19].…”

Section: Modeling Of Surfactant Effectsmentioning

confidence: 99%

Droplet formation in microfluidic T-junction generators operating in the transitional regime. III. Dynamic surfactant effects

Glawdel

Ren

2012

Phys. Rev. E

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This study extends our previous work on droplet generation in microfluidic T-junction generators to include dynamic interfacial tension effects created by the presence of surfactants. In Paper I [T. Glawdel, C. Elbuken, and C. L. Ren, Phys. Rev. E 85, 016322 (2012)], we presented experimental findings regarding the formation process in the squeezing-to-transition regime, and in Paper II [T. Glawdel, C. Elbuken, and C. L. Ren, Phys. Rev. E 85, 016323 (2012)] we developed a theoretical model that describes the performance of T-junction generators without surfactants. Here we study dynamic interfacial tension effects for two surfactants, one with a small molecular weight that adsorbs quickly, and the other with a large molecular weight that adsorbs slowly. Using the force balance developed in Paper II we extract the dynamic interfacial tension from high speed videos obtained during experiments. We then develop a theoretical model to predict the dynamic interfacial tension in microfluidic T-junction generators as a function of the surfactant properties, flow conditions, and generator design. This model is then incorporated into the overall model for generator performance to effectively predict the size of droplets produced when surfactants are present.

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Surfactant Adsorption to Spherical Particles: The Intrinsic Length Scale Governing the Shift From Diffusion to Kinetic-Controlled Mass Transfer

Cited by 76 publications

References 15 publications

Interfacial Rheology Through Microfluidics

Interfacial Rheology Through Microfluidics

Microscale tipstreaming in a microfluidic flow focusing device

Droplet formation in microfluidic T-junction generators operating in the transitional regime. III. Dynamic surfactant effects

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