Measuring Interfacial Tensions of Micrometer-Sized Droplets:  A Novel Micromechanical Technique

A microcantilever technique is developed to directly measure interfacial tensions at the surfaces of emulsion drops. This technique involves distorting (stretching) an otherwise spherical droplet using two suction pipets and quantifying the stretching force with a glass cantilever. From the experimental force−drop deformation relation, which is well described by the Young−Laplace equation, the interfacial tension can be determined. This method of “in situ tensiometry” is applied to emulsions composed of simple liquids, and the results are in good agreement with literature values. At present, the microcantilever technique has attained a resolution of ±1 mN/m. It has also opened the possibility of directly examining transport processes and rheological properties at the surfaces of emulsion drops and other similarly sized microvolumes, such as food colloids or the microcapsules employed in drug delivery.