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. Hexadecane droplets were formed in ethanol-water solutions with a range of static interfacial tensions to derive a calibration curve, which was subsequently used to access the dynamic interfacial tension of hexadecane droplets formed in surfactant solutions. For SDS and Synperonic PEF108, various continuous- and disperse-phase (hexadecane) flow rates were studied, and these conditions were linked to interfacial tension effects, which also allowed convective transport of surfactants to be investiagted. On the basis of these findings, various strategies for the formation of emulsion droplets can be followed and are discussed.