Surface tension determination through measurements of resonance oscillation of a small surface using dielectric force by a localized alternating current electric field.

The present study proposed a novel microscope method for the determination of the surface tension of liquids through measurements of the forced oscillation of the small surface, which was induced with a rod electrode by applying an alternating current (ac) voltage. The electrode bottom was placed 200 μm above the surface, and a stronger electric field was generated under it. Liquids of a larger dielectric constant than air gathered under the electrode by a dielectric force, and thus the surface was oscillated. The oscillation was successfully analyzed with the forced oscillation model and the oscillation mode of two-dimensional circular membranes. A resonance oscillation was observed, the frequency of which was well related to the ratio of surface tension to density of the liquids. Therefore, the proposed novel method can be used for the determination of surface tensions of small surfaces with known densities.