Interfacial Rheology Through Microfluidics

Abstract

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.

Emulsion Drops with Complex Interfaces: Globular Versus Flexible Proteins

“…[85] in detail by several authors. [86][87][88][89][90][91][92] For example, Hu and Lips [86] used progressively subdivided generations of daughter drops to prepare a collection of interfaces with well-defined surface coverage and studied the effect of interface dilatation and Marangoni stresses on the drop deformation at different viscosity ratios. Bazhlekov et al [87] studied similar effects using numerical simulations combining the boundary integral and finite element methods.…”

Microfluidic analysis of cellular deformability of normal and oxidatively damaged red blood cells

“…A potentially promising, cost-effective, and high throughput method for measuring RBC deformability is microfluidics [35][36][37][38][39][40][41]. Deformability measurements using microfluidics uses minute amounts of a whole blood or RBC suspension flowing through a funnel-shaped microconstriction [42][43][44].…”

Microfluidic methods to study emulsion formation

“…It should be mentioned that these differences were reported for equilibrated films that take hours to form, and these conditions were most probably not met in the short microfluidic experiments, but our findings might be indicative of the fact that these effects occur very early on in film formation. In order to determine this, interfacial rheology would need to be determined in the millisecond time-scale, which may be possible through interfacial mobility measurement with microfluidics (Martin et al 2011;Schwalbe et al 2011;Erk et al 2012), but this is considered outside the scope of the present work.…”

“…Microfluidic devices can also be used to measure interfacial mobility (Martin & Hudson 2009;Martin et al 2011), and dilatational interfacial rheology (Schwalbe et al 2011;Erk et al 2012), which are important parameters to quantify because of their role in droplet coalescence stability: interface immobilisation reduces film drainage (Martin et al 2011), and film rupture can be seen as dilatational deformation (Bos & van Vliet 2001). For such measurements, particle movement at the interface is tracked (Figure 7.2A), and from these images interfacial mobility was determined (Figure 7.2B).…”

“…Superimposed images of a flowing droplet illustrating the internal flow pattern with streak lines that visualise polystyrene tracer particle motion at the oil-water interface (A), and from which the internal drop circulation was measured as a function of the interfacial tension for different butanol concentrations (0 (*), 0.5 (X), 1 (▲), 2 (■), and 5 (♦) %) (B). From Martin et al (2011) and Martin and Hudson (2009).…”