Interfacial Rheology Through Microfluidics

• Published in: Advanced materials (Weinheim) 2011-01, Vol.23 (3), p.426-432
• Main Authors: Martin, Jeffrey D., Marhefka, Joie N., Migler, Kalman B., Hudson, Steven D.
• Format: Article
• Language: English
• Subjects: Animals; complex fluids; Devices; Droplets; emulsions; Erythrocytes - physiology; interfacial rheology; Interfacial tension; Joining; Mass transfer; Microfluidic Analytical Techniques; Microfluidics; Mineral Oil - chemistry; Rheology; Surface-Active Agents - chemistry; Surfactants
• ISSN: 0935-9648; 1521-4095; 1521-4095
• DOI: 10.1002/adma.201001758

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. Using a microfluidic device that facilitates the measure of interfacial tension in two‐phase droplet flows, particle tracers are placed inside the droplet phase and the internal circulation velocity is used as a measure of interfacial mobility. Thus interfacial tension, interfacial retardation (Marangoni effects), and surfactant mass transfer can be measured in the same experiment and at industrially relevant size scales and flow types.