title: Measurement of surface and interfacial tension using pendant drop tensiometry.
abstract: Pendant drop tensiometry offers a simple and elegant solution to determining surface and interfacial tension - a central parameter in many colloidal systems including emulsions, foams and wetting phenomena. The technique involves the acquisition of a silhouette of an axisymmetric fluid droplet, and iterative fitting of the Young-Laplace equation that balances gravitational deformation of the drop with the restorative interfacial tension. Since the advent of high-quality digital cameras and desktop computers, this process has been automated with high speed and precision. However, despite its beguiling simplicity, there are complications and limitations that accompany pendant drop tensiometry connected with both Bond number (the balance between interfacial tension and gravitational forces) and drop volume. Here, we discuss the process involved with going from a captured experimental image to a fitted interfacial tension value, highlighting pertinent features and limitations along the way. We introduce a new parameter, the Worthington number, Wo, to characterise the measurement precision. A fully functional, open-source acquisition and fitting software is provided to enable the reader to test and develop the technique further.
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation (CSIRO) Mineral Resources Flagship, Clayton 3169, Australia; Department of Chemical and Biomolecular Engineering, University of Melbourne, Parkville 3010, Australia.
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Berry
authors.affiliation: School of Mathematics and Statistics, University of Melbourne, Parkville 3010, Australia.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Neeson
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Melbourne, Parkville 3010, Australia; Melbourne Centre for Nanofabrication, 151 Wellington Road, Clayton 3168, Australia.
authors.forename: Raymond R
authors.initials: RR
authors.lastname: Dagastine
authors.affiliation: School of Mathematics and Statistics, University of Melbourne, Parkville 3010, Australia; Department of Chemistry and Biotechnology, Swinburne University of Technology, Hawthorn 3122, Australia.
authors.forename: Derek Y C
authors.initials: DY
authors.lastname: Chan
authors.affiliation: School of Chemistry, Monash University, Clayton 3800, Australia. Electronic address: Rico.Tabor@monash.edu.
authors.forename: Rico F
authors.initials: RF
authors.lastname: Tabor
keywords: Bond number; Drop shape analysis; Interfacial tension; Pendant drop; Surface tension; Tensiometry