Measuring interfacial tensions of micrometer-sized droplets: A novel micromechanical technique

A microcantilever technique is developed to directly measure interfacial te nsions at the surfaces of emulsion drops. This technique involves distortin g (stretching) an otherwise spherical droplet using two suction pipets and quantifying the stretching force with a glass cantilever. From the experime ntal 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, t he 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 similarl y sized microvolumes, such as food colloids or the microcapsules employed i n drug delivery.