Non-contact methods for measuring the surface tension of liquids (review)

Abstract

A review of non-contact methods for determining the surface tension of liquids along with analysis of the physical effects underlying them is presented. A review of non-contact methods for determining the surface tension of liquids along with analysis of the physical effects underlying them is presented. The advantages, disadvantages, possible ranges of measurements and scope of non-contact methods are discussed. Passive methods do not require any stimulation of the measurement object whereas active methods, when implemented, affect the liquid under study. Electrical, electromagnetic, acoustic, jet, and mechanical methods used for excitation of capillary waves are described in analysis of the methods based on capillary waves intended to study the properties of surface-active substances. We also considered methods based on the processes occurred in an oscillating or rotating levitating drop of liquid (containerless technology) used to study the properties of melts and methods based on local deformation of the liquid surface by the electric field, acoustic pulse, and gas jet. It is shown that aerodynamic methods based on deformation of the liquid surface under control by a gas stream are the most promising for standard laboratory conditions. It is noted that containerless methods should be used in zero gravity tests, whereas the methods based on capillary waves or deformation of the liquid surface with a focused acoustic pulse appeared useful in testing inviscid liquids. Methods based on electrical deformation of the liquid surface under control are limited with the thickness of the liquid layer, relatively high sensitivity to the density and dielectric constant of the liquid, and some other uncontrolled factors. It was also noted that aerodynamic non-contact method of the surface tension determination is characterized by low sensitivity to the density and viscosity of the controlled liquid. The presented review of non-contact methods of the surface tension determination provides optimal choice of the method most suited for solving specific measurement problems.