Interfacial TensiometerThe interface in the middle refers to the transition zone with a thickness of several molecules in contact between two phases, such as when one phase is a gas, this interface is usually referred to as the surface. At the interface between solid and liquid, or at the interface between two different liquids, the sum of the excess free energies of molecules of two substances per unit area relative to the same number of molecules inside the phase is called interfacial tension.

The interfacial tension between gas and liquid, also known as the surface tension of liquid, is the interfacial tension between liquid and air.

Interface tension meters can be divided into two types based on different testing principles: platinum ring method and platinum plate method.

The platinum ring test is a traditional testing method that has been around for about 70 years since its invention. It is a ring made of platinum wire with a certain circumference. During testing, immerse the platinum ring 2-3mm below the interface (or liquid surface) of two immiscible liquids, and then slowly lift the platinum ring upwards, forming a film between the ring and the liquid surface. The membrane exerts a downward force on the platinum ring, and the maximum force exerted by the membrane on the ring during the entire platinum ring lifting process is measured, which is then converted into the true interfacial (surface) tension value.

The history of platinum plate method application is less than 20 years abroad, and it entered China even later. The surface/interface tension meter based on the platinum plate method has high technical requirements and manufacturing difficulties. In recent years, it has been widely used by domestic users with the successful development and market launch of fully automatic surface/interface tension meters using the domestic platinum plate method.

The platinum plate method uses a 24mm × 10mm × 0.1mm platinum plate with sandblasting roughening treatment on the surface to better wet the measured liquid. When testing, gently touch the platinum plate to the interface (or surface). Due to the surface tension of the liquid, the platinum plate will be pulled down. When the surface tension and other related forces of the liquid reach equilibrium with the reverse force of the instrument test, the test value will remain stable. If it is pure substances such as distilled water and ethanol, the entire testing process will be as fast as a few seconds.