A tensiometer is an instrument used to measure the surface tension (γ) of liquids or surfaces in the domain of physics.
Surface tension is the contractive quality of the surface of a liquid that allows it to resist external force. For example, surface tension causes certain objects on the surface of water to float even though they are denser than water. Similarly, surface tension can be seen in the ability of some insects like the water strider to run on the water surface. Surface tension is caused by cohesion of similar molecules, and is responsible for many of the behaviors of liquids.
The surface tension of water at room temperature is around 70 dynes/cm, and at freezing point, it is close to infinity. As the liquid reaches boiling temperature, the surface tension of the water moves toward 0.
Different Types of Surface Tension Tensiometer
The following are the different types of surface tension tensiometer:
- Goniometer/Tensiometer - is used to measure the surface tension and interfacial tension of a liquid using the pendant or sessile drop techniques.
- Du Noüy Ring Tensiometer - uses a platinum ring that is submersed in a liquid. When the ring is pulled out of the liquid, the tension required is measured to determine the surface tension of the liquid. There are two types of ring tensiometers - the interfacial tensiometer and the other is a plain tensiometer. The plain tensiometer works only with an upward pull and the interfacial works with both an upward pull as well as a downward push. Interfacial tension is basically the force that keeps the surface of one liquid from invading the surface of another liquid. To measure the interfacial tension of water and oil, the platinum ring in the interfacial tensiometer is pulled through the surface of the water into the oil. The water tends to adhere to the ring for some distance above the surface. When it breaks away, the force is measured and converted to interfacial surface tension.
- Wilhelmy Plate Tensiometer - uses a plate that makes contact with the liquid surface. The plate is placed perpendicular to the interface, and the force exerted on it is measured. Surface scientists consider this tensionmeter the simplest and most accurate for measuring surface tension.
- Bubble Pressure Tensiometer - used to determine the surface tension of liquids from the pressure in gas or air bubbles that are generated in the measuring liquid with a capillary of known dimensions.
Manufacturers of Tensiometers
There are a wide range of tensiometers options in the market today. The following is a list of various rheometer producers with a brief introduction of their products:
- Attension, a global provider of analytical instruments, provide a variety of tensiometers. Sigma 700/701 is an ideal option to measure surface tension. Sigma force tensiometers and theta optical tensiometers can also be used based on the requirement and experimental constraints. For dynamic surface tension, Attension provides the BPA-800P bubble tensiometer.
- TECLIS is a leader in the instrument market of physical chemistry of surfaces and interfaces. They provide a range of tensionmeters. The Tracker™ is an automated drop tensiometer that can measure variations in surface tension or interfacial tension over time. The Tracker™ can also measure the contact angle of a liquid against a solid. A variety of optional lenses are provided, thus enabling the lower limit of interfacial tension measurement to be less than 0.1 mN/m. The Tracker™ is available in three versions - Tracker H, Tracker S, and Tracker M.
Applications of Tensiometers
The key areas of application of the tensiometers are listed below:
- In research and development laboratories to determine the surface tension of liquids like coatings, lacquers or adhesives
- For monitoring industrial production processes like part's cleaning or electroplating
- For monitoring the detergent concentration in cleaning or electroplating processes
- To determine not only surface tension measurements but also powder wettability, absorption, cleanliness, surface heterogeneity and density.
Sources and Further Reading