Jeffrey D Martin and Steven D Hudson 2009 New J. Phys. 11 115005 doi:10.1088/1367-2630/11/11/115005
Mass transfer and interfacial properties in two-phase microchannel flows
Focus on Micro- and NanofluidicsJeffrey D Martin1 and Steven D Hudson1
Show affiliationsPart of Focus on Micro- and Nanofluidics
Drop-based microfluidic devices are becoming more common, and molecular mass transfer and drop circulation are issues that often affect the performance of such devices. Moreover, interfacial properties and surfactant mass transfer rates govern emulsion behavior. Since these phenomena depend strongly on drop size, measurement methods using small drops and flow typical of applications are desired. Using mineral oil as a continuous phase, water droplets and an alcohol surfactant, we demonstrate here a microfluidic approach to measure the interrelated phenomena of dynamic interfacial tension, surfactant mass transfer and interfacial retardation that employs droplet flows in a microchannel with constrictions/expansions. Interfacial flow is influenced markedly by adsorption of surfactant: severe interfacial retardation (by a factor of 30) is observed at low surfactant concentrations and interface remobilization is observed at higher surfactant concentrations. The interfacial tension is described by Langmuir kinetics and the parameters for interfaces with mineral oil (studied here) compare closely with those previously found at air interfaces. For the conditions explored, the surfactant mass transfer is described well by a mixed kinetic-diffusion limited model, and the desorption rate coefficients are measured to be both approximately 70 s−1. The transition from a diffusion-controlled to mixed diffusion-kinetic mass transfer mechanism predicted with reducing drop size is verified. This experimental approach (i.e. adjustable geometry and drop size and height) can therefore probe interfacial dynamics in simple and complex flow.
- PACS
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47.60.-i Flow phenomena in quasi-one-dimensional systems
83.80.Qr Surfactant and micellar systems, associated polymers
82.20.Pm Rate constants, reaction cross sections, and activation energies
68.03.Cd Surface tension and related phenomena
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
- Subjects
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Soft matter, liquids and polymers
Surfaces, interfaces and thin films
- Dates
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Issue 11 (November 2009)
Received 1 June 2009
Published 4 November 2009
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Mass transfer and interfacial properties in two-phase microchannel flows
Jeffrey D Martin and Steven D Hudson 2009 New J. Phys. 11 115005
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