Surface tension is the ability of a liquid surface to resist external forces and is often described as the result of the attraction of liquid molecules to each other. The magnitude of the surface tension depends on the type of liquid and the properties of its contact with other substances. To measure the surface tension of liquids, scientists and engineers have invented a variety of methods, two of which are the surface tension test plate method and the ring method.
Surface Tension Test Plate Method:
In the surface tensile test plate method, a simple device is usually employed that includes a closed container and a thin plate or test plate that floats on the surface of the liquid. The steps are as follows:
Fill the liquid to be measured in a closed container to ensure that the surface of the liquid is flat and does not come into contact with the container wall.
Gently place the test plate on the surface of the liquid so that it floats above the liquid.
The depth of immersion of the test plate in the liquid is measured and recorded. In general, the greater the surface tension of the liquid, the less the depth of immersion of the test plate in the liquid.
By measuring the depth of immersion and the weight of the test plate, using a suitable formula or graph, the surface tension value of the liquid can be calculated.
Surface Tension Test Ring Method:
The ring method, also known as the wire drawing method, is mainly used for surface tension measurements on small droplets or rings of liquid. The steps are as follows:
Load the liquid to be measured into a ring to ensure that the liquid fills the entire annular space and forms a liquid ring.
Slowly lift the ring upwards until the liquid ring stretches out of the ring until it breaks. In this process, the required force and the circumference of the ring are measured.
By measuring the required force and the circumference of the ring, using an appropriate formula, the surface tension value of the liquid can be calculated.
The difference between the plate method and the ring method
Both the surface tension test plate method and the ring method are used to measure the surface tension of liquids, and their main differences are in the shape of the sample and the measuring principle:
Surface Tension Test Plate Method:In the surface tension plate method, a liquid sample is placed in a closed container so that it forms a horizontal surface. Then, a sheet or plate is placed on the surface of the liquid so that it floats on the surface of the liquid. The surface tension of the liquid can be calculated by measuring the weight of the plate as well as the depth at which it is immersed in the liquid.
Surface Tension Test Ring Method:In the ring method, a liquid sample is loaded into a ring with one side of the ring in contact with the liquid, forming a liquid ring. Then, gradually lift the ring upwards until the liquid stretches out of the ring to break. The surface tension is calculated by measuring the circumference of the liquid ring and the force required to break.
Main Differences:
The surface tension test plate method is suitable for larger liquid surfaces, while the ring method is suitable for smaller liquid surfaces.
The ring method is more sensitive and accurate for the measurement of the surface tension of liquids, but requires more complex instrumentation and technical operation.
The surface tension test plate method is relatively simple and suitable for surface tension measurements under general laboratory conditions.