Various methods can be used for measuring interfacial tensions. Unlike most other methods, the spinning drop method can be used to measure ultra-low surface tensions of 10-5 mN/m or even 10-6 mN/m.
Measuring principle [1]
A droplet of a liquid of lower density and a surrounding medium of higher density are placed in a rotating glass tube. The droplet shape is determined by the interfacial tension and the centrifugal force. At low angular velocities ω the interfacial tension σ is the dominating force and thus the droplet is spherical. For higher angular velocities the droplet becomes cylindrical. In this case the interfacial tension can be calculated from Vonnegut's equation as 
where R is the radius of a cylindrical droplet and Δρ is the difference of the densities of the droplet and the surrounding medium.
Features [2]
- Temperature controlled measurement cell (Temperature range: -10 – 130 °C)
- LED lighting with software controlled adjustable intensity and strobe frequency
- Video measuring system with USB-camera (max. 146 images/s sample rate)
- High dynamic, electronically commutated direct current motor with software controlled speed control
- High-performance 6-fold power zoom lens
- Automatic, software controlled position and tilt adjustment
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[1] Spinning drop experiments on interfacial phenomena: Theoretical background and experimental evidence, A. M. Seifert, J. H. Wendorff, Colloid Polym Sci, 1992, 270, 962-971. |
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[2] http://www.dataphysics.de/startseite/produkte/spinning-drop-tensiometer/ |
Diana Sottmann
CTA
Abdulhamid Hejazi Almidani
Doctoral Researcher