Researchers at Princeton University have developed a novel technique to measure ultralow interfacial tensions using paramagnetic spheres in a microfluidic co-flow device.  The resulting tensiometry device is accurate, low cost, compact in size, and easy to integrate.

Fluid systems that have ultralow interfacial tensions appear in a range of different applications, including uses in oil and food industries.  However, quantifying ultralow interfacial tensions practically and accurately has remained challenging.  Traditional force tensiometry methods such as Wilhelmy Plate and Du Noüy Ring are not suitable because it is difficult to resolve the small forces experienced by the probes at the interface of ultralow interfacial tension fluids.  Measuring very low interfacial tensions using the spinning drop method is also not ideal since the droplets equilibrate very slowly, making it challenging to determine when to make the measurement.

By using a balance of magnetic and surface forces on the spheres in a microfluidic co-flow, Princeton researchers can measure two-fluid interfacial tension.  The effectiveness of this technique has been experimentally demonstrated by measuring very low interfacial tensions (10-3 ¿ 10-2 mN/m) in solutions of different surfactant concentrations.  It is anticipated that this technique may be scaled up to measure up to 1 mN/m.

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