Contactless interfacial rheology to measure liquid-liquid interfaces

Researchers from ECFP and the Soft Matter Physics group at the University of Edinburgh have developed a new contactless interfacial rheology technique to measure liquid-liquid interfaces matching processing and application conditions.

20 February 2023

The interface between two liquids is vital to the production and stability of many foods and consumer formulations but measuring how interfaces flow is a delicate task. Researchers from ECFP and the Soft Matter Physics group at the University of Edinburgh have developed a new interfacial rheology technique to test how interfaces flow without direct mechanical contact. This matches how interfaces in consumer products are indirectly affected by the flow of liquid as, e.g., as skin cream is applied.

The new contactless technique pushes on an interface by flowing liquid above it (top image) and measures the movement of the interface by microscopy (bottom image). (Image adapted from

Interfacial rheology goes contactless

Conventional interfacial shear rheology attaches a mechanical probe to the interface, many times larger than the stabilising surfactants or particles, and measures the forces as it is pushed along. This limits how sensitive measurements can be and can damage or disturb the interfacial structure. The contactless technique instead pushes on the interface by flowing liquid above it (top image above) and measuring the movement of the interface by microscopy, showing liquid-like flow and solid-like elasticity (lower image above). This enables tests on delicate particle-stabilised interfaces, including those that are of interest when reformulating products with sustainable alternatives to hydrocarbon-derived surfactants.

The work of Iain Muntz, led by Dr Job Thijssen and in collaboration with Dr James Richards, recently published in the Journal of Rheology and featured in a Scilight (Science Highlight), reveals that a model hard-particle stabilised interface aggregates above a critical stress (below). This leads to a weakened structure that has dramatic implications for Pickering emulsion stability.

To explore what interfacial rheology can do for your formulation challenges, please get in touch.

Figure 2. The evolution of a model hard-particle system, showing aggregation above a critical stress.
The structural evolution of model hard particles at an oil-water interface. Microscopy images to the right of the dotted line illustrate aggregation above a certain critical stress (Image adapted from


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