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Surface tension measuring



Due to the density difference between the liquid phase and the gas phase, the molecules in the surface layer of the liquid are subjected to a gravitational force that points to the interior of the liquid phase and is perpendicular to the interface, making the liquid surface like a tensioned elastic film on this film. There is shrinkage tension that causes the liquid surface to shrink to a minimum

What are the main methods of measuring surface tension?

Figure 1: Basic tensionmetry using Du Noüy method
  1. Du Noüy Ring method: This is probably the most classic method for measuring surface/interfacial tension. The surface/interfacial tension values of many liquids reported in the literature are measured by this method. A liquid film (similar to a soap bubble) was pulled from the liquid with a ring initially immersed in the liquid, while measuring the force required to raise the ring high.
  2. Wilhelmy Plate method: also known as the hanging piece method, this is a very common measurement method, especially suitable for the measurement of surface tension for a long time. In this method, only a sufficient volume of liquid needs to be provided, and no other parameters need to be provided. In fact, other geometric probes such as round rods, balls, etc. can be used to replace the plate. The measurement principle is the same, which is called the improved Wilhelmy plate method.
  3. Pendant drop method: It is an interface shape analysis method, which is based on the analysis of an interface shape in a force equilibrium state. It is an optical analysis method suitable for the measurement of interfacial tension and surface tension, and canalso be used in very high Measurements are made at pressure and temperature, and when making measurements, it is necessary to know the two-phase substances and their densities.

What is the difference between surface tension and interfacial tension

The surface tension of a liquid is measured in air, while the interfacial tension is the tension between two immiscible liquids such as water and oil, there is no interfacial tension between two miscible liquids.