Novel method for measuring surface tension

E.S. ten Hav, G. Vdovin
Sensors and Actuators A: Physical, Volume 173, Issue 1, January 2012

Abstract

It is shown that the observed geometry of an electrostatic deformation of a liquid surface can be used for the measurement of surface tension. Based on simulations and measurements, an empirical formula for the relation between the shape of the deformation and the surface tension is derived and discussed. A novel method for high resolution measurements of the surface tension using interferometry of an electrostatically deformed liquid surface is presented and investigated.

Additional information:

The principle of electrostatic deformation of a liquid surface can also be applied to the correction of aberrated optical beams where the liquid-air interface is used as a deformable mirror. Here, the dynamic behavior of the system strongly depends on the physical properties of the liquid, of which the surface tension is the most difficult to determine. The behavior of the liquid also depends on the shape of the container which can be determined easily with high precision. Macroscopic movement of the liquid surface may be excited which can be described with the normal modes of the system. Only when the properties of the liquid are known can the resonant and oscillatory behavior of the system be modeled correctly. The figure shows the measured rms error of an aberratedwavefront (top) as a function of time with (left) and without correction (right). The corresponding far field intensity distributions are shown at the bottom.
The results show that knowledge of the physical properties of the liquid system can be used to correctly model the behavior of an electrostatically deformed liquid-air interface, so that it can be manipulated to correct an aberrated beam in a closed-loop adaptive optical system. See also our recent publication in Applied Optics, Volume 51, Number 12 (2012).

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