Facility Details
DCA 100 by Camtel Ltd
Dynamic Contact Angle Tensiometer, used for measuring the surface energies of solids and the surface tension of liquids.
The DCA 100 is used to measure the tension at liquid/gas and liquid/liquid interfaces. For these purposes the term interface is used to cover the boundary between phases.
Within the bulk of a liquid the molecules are completely surrounded by other molecules such that the forces of attraction are equal in all directions but at the interface there are ‘unsatisfied’ forces resulting in an inward attraction. This is what causes small drops to assume a spherical shape and soap films to contract.
The universally accepted technique for measuring liquid/gas surface tension is by the Du Nouy ring that has a precise geometry made of Pt-Ir alloy. International standards for both liquid/gas and liquid/liquid interfaces are based on this technique. The standards have been adopted by a number of industries such as water and environmental as well as rubber and surfactants. The measurement simply requires the ring to be wetted by the liquid and then pulled through the interface while measuring the force exerted on the ring.
An alternative geometry for measuring interfacial tension is the Wilhelmy plate that is made from roughened platinum but can be pre-wetted paper or glass with a hydrophilic coating. In this technique the plate is suspended at the interface and maintained in this position by a force that balances the weight of the plate and the meniscus force of the liquid acting on the lower edge of the plate.
One major difference between the ring and the plate is the way in which the measurement is carried out (the ring is moves throughout whereas the plate is static). Therefore there is no ‘artificial’ disturbance of the interface and no increase in the time to reach equilibrium when using the plate method.
Within the bulk of a liquid the molecules are completely surrounded by other molecules such that the forces of attraction are equal in all directions but at the interface there are ‘unsatisfied’ forces resulting in an inward attraction. This is what causes small drops to assume a spherical shape and soap films to contract.
The universally accepted technique for measuring liquid/gas surface tension is by the Du Nouy ring that has a precise geometry made of Pt-Ir alloy. International standards for both liquid/gas and liquid/liquid interfaces are based on this technique. The standards have been adopted by a number of industries such as water and environmental as well as rubber and surfactants. The measurement simply requires the ring to be wetted by the liquid and then pulled through the interface while measuring the force exerted on the ring.
An alternative geometry for measuring interfacial tension is the Wilhelmy plate that is made from roughened platinum but can be pre-wetted paper or glass with a hydrophilic coating. In this technique the plate is suspended at the interface and maintained in this position by a force that balances the weight of the plate and the meniscus force of the liquid acting on the lower edge of the plate.
One major difference between the ring and the plate is the way in which the measurement is carried out (the ring is moves throughout whereas the plate is static). Therefore there is no ‘artificial’ disturbance of the interface and no increase in the time to reach equilibrium when using the plate method.