(160h) A Microfluidic Platform to Measure Dynamic Interfacial Tension of Complex Fluid Systems

Liquid-liquid emulsions are central to many applications, including food processing, oil recovery, liquid filtration as well as environmental science. The accurate and rapid determination of interfacial tension is vital for characterizing their formation and stability behavior. Microfluidics has emerged as a powerful tool for measuring such fundamental properties in a cost-effective and reproducible manner, with low sample volumes and high throughput¹. Such measurements employ optical microscopy and high-speed imaging to record droplet shape deformation in a contraction-expansion geometry, and further use the parameters extracted from image analysis to calculate interfacial tension using existing theory^2-4. While applicable to many systems, the underlying assumptions of the theory can limit its application to particularly complex emulsions.

In this work, microfluidic tensiometry experiments are implemented to characterize interfacial properties of water droplets in complex, low viscosity diesel-fuel systems. Diesel fuel systems are multicomponent mixtures containing additives which significantly lower the interfacial tension and hinder the coalescence of water droplets dispersed in the fuel. The dynamic interfacial behavior exhibited by these systems has remained largely unexplored, despite the significant impact that they have on coalescence. This work uses microfluidic drop-shape analysis in contraction-expansion geometries to study how liquid properties, flow conditions, and device geometries can impact the measurement of dynamic interfacial tension. Empirical measurements are also compared to those based on theory. This analysis will enable accurate prediction of interfacial tension in complex, low viscosity liquid-liquid systems, using high-throughput microfluidics. The results of this work reveal new insights into the dynamics of additive transport to fuel-water interfaces.

References:

(1) Cabral, João T., and Steven D. Hudson. "Microfluidic approach for rapid multicomponent interfacial tensiometry." Lab on a Chip 6.3 (2006): 427-436.

(2) Taylor, G. I. "The viscosity of a fluid containing small drops of another fluid." Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character 138.834 (1932): 41-48.

(3) Taylor, G. I. "The formation of emulsions in definable fields of flow." Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character 146.858 (1934): 501-523.

(4) Rallison, J. M. "The deformation of small viscous drops and bubbles in shear flows." Annual Review of Fluid Mechanics 16.1 (1984): 45-66.