Measurement of interfacial tension by drop retraction analysis

The retraction of a deformed drop back to the spherical, equilibrium shape at rest has been the subject of several studies in the literature with the aim of measuring the interfacial tension between the drop and the continuous phase. In this work, the retraction of a drop deformed under the action of a shear flow was analyzed by using the theoretical approach proposed by Rallison in the limit of small deformations. A single exponential decay was then obtained for the time evolution of the deformation parameter in the course of retraction. By fitting such expression to the experimental data the interfacial tension can be determined. Experiments of drop retraction were performed by using a parallel plate apparatus. The experimental trend of the deformation parameter during retraction was well represented by a single exponential decay and the calculated interfacial tension was in good agreement with values reported in the literature for the system investigated. A detailed comparison of the proposed analysis of drop retraction with other methods available in the literature is also presented. (C) 1999 Academic Press.