April 2009

Interfacial Tension is a lot like surface tension except that the external phase is a liquid instead of a gas. The drop and external phases are immiscible liquids. If the drop liquid is denser than the external phase, a hanging pendant drop is used. In most cases, however, the drop is less dense and so an inverted pendant drop is used.

Interfacial tension explains the attractive forces between the molecules of different liquids at the interface (or surfaces between them). It is measured in newtons per meter (mN/m) which is the same as dynes per cm and is a unit of force per unit length typically represented by γ. Interfacial tension is important to the study of colloidal systems -- in particular emulsions. An emulsion is a mixture of two immiscible liquids such as an oil (the dispersed phase) and water (the continuous phase). An emulsifier is used to keep the dispersed liquid from aggregating. It does this by lowering the interfacial tension. Often the emulsifier is a surfactant. Take mayonnaise, for example, which is an oil-in-water emulsion stabilized with egg yolk. The egg yolk lecithin acts as the emulsifier and is a natural amphoteric surfactant.

In the oilfield, heat and mechanical forces are used in addition to emulsifiers to form an emulsion. As the interfacial tension increases, greater energy is required to form a stable emulsion. Just as surface tension decreases as temperature increases so too interfacial tension is lower at elevated temperatures. On the flipside, chemicals called demulsifiers are used to break down emulsions. Through the process of demulsification, salt water can be removed from crude oil prior to refining.

The video above (also available here: http://tinyurl.com/dyf5m6) illustrates how easy it is to create an interfacial tension experiment using DROPimage Advanced. In order to carry out this study, a Model 250 or 500 is required with DROPimage Advanced. We also used the Environmental Fixture (p/n 100-07-60) and a 22 gauge inverted needle (p/n 100-10-13-22). Other sizes are available from 13 to 30 gauge. If you need to make interfacial tension measurements at an elevated temperature, then in lieu of the Environmental Fixture, the Environmental Chamber (p/n 100-07) and mating Quartz Cell (p/n 100-07-50) along with the Proportional Temperature Controller (p/n 100-50) can be employed on a Model 500.

In addition to the above video, we also created a knol which can be viewed here: http://tinyurl.com/creexb. The article goes through each of the steps shown in the video and explains step-by-step the procedure for creating and running a new interfacial tension experiment using the DROPimage Experiment Wizard tool.

On a related note, we also created a similar knol on measuring surface tension with DROPimage Advanced. It can be accessed here: http://tinyurl.com/ckehfw

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A symposium on "Nanostructured Surfaces and Surfaces of Nanostructures" will be held at the upcoming Canadian Chemistry Conference and Exhibition which is being held in Hamilton, Ontario from May 30 to June 3, 2009. According to Dr. Matthias Geissler, this symposium will bridge the gap between the surface science community and the nanomaterials community. For more details, go to http://tinyurl.com/c3buak.