Interfacial Elasticity Measured by the Oscillating Drop Method

High interfacial elasticity correlates with low coalescence and, thus, stable foams, e.g., in milk shakes or cappuccino. The best stabilizers can be found by performing interfacial rheolgy studies with the oscillating drop method. This is easily possible with the optical drop shape analysis systems from DataPhysics Instruments.

Emulsifiers and Stabilizers for Food Products

When new food products, for example for instant drink powders, are developed, it is important to find the best emulsifiers and stabilizers. These surface-active molecules must ensure a low surface tension and interfacial tension, which allows a fine dispersive mixture of the different components. Moreover, they should enhance the interfacial elasticity in order keep the generated foams and emulsions stable.

Study of Interfacial Tension and Viscoelasticity

The surface and interfacial tension of a liquid can easily be measured in a pendant drop experiment. The OCA system from DataPhysics Instruments returns the result within seconds. Quite conveniently, the same instrument can be used to study interfacial viscoelasticity. Without changing any part of the instrumentation, the user simply choses the Oscillating Drop method.

Oscillating Drop Experiments

To study interfacial viscoelasticity DataPhysics Instruments’ electronic syringe module periodically increases and decreases the volume of a pending drop while the camera of the measuring system captures the changing drop shape. The software analyses the sinusioidally increasing and shrinking drop area A, as well as the interfacial tension σ.

The Measurement Principle

Two oscillating curves (A, σ) are measured. Their phase shift determines the viscoelastic parameters of the studied system: If the phase shift is big, this indicates that the interface behaves rather viscous. Accordingly, one obtains a comparably high interfacial dilatation viscosity modulus, E’’. In this case, the surface-active molecules hop on and off the interface as they try to compensate its depletion or over-population caused by the drop enlarge- and diminishment, respectively. If, on the other hand, an exchange of surface-active molecules between bulk solution and interface is not possible or hindered, a minor phase shift between the oscillating measuring curves is found. The interfacial dilatation elasticity modulus, E’, is high, respectively, and one says the interface behaves elastic.

Easy Measurement, Fast Results

The calculation of the interfacial dilatation moduli, just as the execution of the whole experimental procedure, is of course automatically performed by DataPhysics Instruments’ software. Hence, as a user you obtain with ease valuable information about your system that allows you to tune and optimize your product.

If you want to know more about the oscillating drop method and all the other capabilities of DataPhysics Instruments’ OCA systems visit, just give us a call (+49 711 77 05 56 0) or drop us a line (

We are eager to share our expertise and tailor an optimal solution for your measurement needs.

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