In Boulder, Colorado researchers have developed a sensor that measures interfacial tension to help industrial engineers test new product formulations.

The National Institute of Standards and Technology scientists say they expect their microfluidic instrument to be especially useful for testing interfaces between complex fluids for applications involving scarce amounts of the fluids to be tested.

Interfacial tension is the tendency of chemical components in some products — such as detergent, cosmetics or paint — to mix well and not bead and pull away from each other.

The newly-developed instrument involves a series of channels ranging from 700 micrometers to 50 micrometers wide. Fluids are pumped toward a T intersection where drops of one liquid are pinched off and flow along a river of the second liquid. As the spherical drops flow through constriction points in the channel, they increase speed and elongate.

The degree to which the drops stretch depends on the interfacial tension between the two fluids, researchers said. High levels of tension exert more pressure on the drops, keeping them more nearly spherical.

The researchers — J.T. Cabral and S.D. Hudson — report their work in the March issue of the journal Lab on a Chip.