THE MEASUREMENT OF ULTRALOW INTERFACIAL-TENSION BY VIDEO DIGITAL-TECHNIQUES

A video image processor is used to extend the range of interfacial tension measurement using the inflection plane method of pendant drops to the ultralow tension region. The success of the technique relies on the choice of drop geometry. Drops containing a neck are unsuitable since this introduces an inherent instability which is accentuated at ultralow interfacial tension. However, pendant drops without an equator but still having an inflection plane have been found to be stable and suitable for the present study. These drops have the magnitude of the shape parameter, β, more negative than 1.3. The drop shape can be controlled by the choice of capillary tip diameter. Interfacial tension results for the two-phase system: n-hepatane:propan-1-ol:water are reported as the system approaches the consulate point. Results into the micro-Newton per meter range have been obtained. © 1990.