title: Microfluidic ultralow interfacial tensiometry with magnetic particles.
abstract: We describe a technique that measures ultralow interfacial tensions using paramagnetic spheres in a co-flow microfluidic device designed with a magnetic section. Our method involves tuning the distance between the co-flowing interface and the magnet's center, and observing the behavior of the spheres as they approach the liquid-liquid interface-the particles either pass through or are trapped by the interface. Using threshold values of the magnet-to-interface distance, we make estimates of the two-fluid interfacial tension. We demonstrate the effectiveness of this technique for measuring very low interfacial tensions, O(10(-6)-10(-5)) N m(-1), by testing solutions of different surfactant concentrations, and we show that our results are comparable with measurements made using a spinning drop tensiometer.
authors.affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Scott S H
authors.initials: SS
authors.lastname: Tsai
authors.forename: Jason S
authors.initials: JS
authors.lastname: Wexler
authors.forename: Jiandi
authors.initials: J
authors.lastname: Wan
authors.forename: Howard A
authors.initials: HA
authors.lastname: Stone