Capillary pressure-based measurement of dynamic interfacial tension in a spontaneous microfluidic sensor.

The size of droplets and bubbles, and the properties of emulsions and foams strongly depend on dynamic interfacial tension () - a parameter that is often inaccessible due to the very short time scales for droplet and bubble formation, and the inaccessibility of (, food) production lines. To solve this challenge, we developed a microfluidic tensiometer that can measure by monitoring the formation time of both droplets and bubbles. Our tensiometer is a pressure-driven microfluidic device that operates based on the principle of a pressure balance: the formation of a droplet (or a bubble) is initialized when the Laplace pressure of the interface is decreased below the externally applied pressure, and this decrease is caused by a reduction in that can be calculated from the applied pressure and the Young-Laplace equation.

Dynamic interfacial tension measurements with microfluidic Y-junctions.

Emulsification in microdevices (microfluidic emulsification) involves micrometer-sized droplets and fast interface expansion rates. In addition, droplets are formed in less than milliseconds, and therefore traditional tensiometric techniques cannot be used to quantify the actual interfacial tension. In this paper, monodisperse droplets formed at flat microfluidic Y-junctions were used to quantify the apparent dynamic interfacial tension during (microfluidic) emulsification.

Characterization of emulsification at flat microchannel Y junctions.

Y junctions with a large width-to-depth ratio were used for the emulsification of hexadecane in various ethanol-water mixtures with different static interfacial tension and viscosity. The resulting droplets were monodisperse. To describe droplet size a force-balance model was derived and was found to apply well.