Interfacial rheology of complex interfaces in emulsions and foam

Foam, emulsions and microencapsulation systems tend to have very high surface to volume ratios, and their macroscopic behaviour is therefore often dominated by interfacial properties. For this reason these materials can be considered Interface Dominated Materials (IDMs). For a targeted design of IDMs with specific functional properties, a detailed understanding of the surface properties (surface tension, bending rigidity, surface rheological parameters, permeability), their relation to structural properties on the microscale, and their relation to macroscopic behaviour, is absolutely essential.

In food IDMs are typically stabilized by proteins, low molecular weight surfactants, colloidal particles (Pickering stabilization), or mixtures of these components. These materials tend to organize themselves into complex 2D structures after adsorption to the interface, such as 2D gels, 2D glass phases, 2D dispersions (mixtures of immiscible surfactants), or 2D (liquid) crystal phases. As a result, the response of these interfaces to a deformation is often nonlinear, even at small deformations. Interfaces can display strain thinning behaviour, strain hardening behaviour, thixotropy, and yielding.

Aim of this project is to investigate the nonlinear rheological properties of complex interfaces using large amplitude oscillatory shear and dilatational deformations, and link these to:

• The microstructure of the interface
• The behaviour and stability of IDMs, such as foam and emulsions.
  

Systems of interest are:

• Protein stabilized interfaces
• Protein-lipid systems
• Pickering systems
• Pickering-lipid interfaces
  

Techniques that will be used are:

• Dilatational rheology, using profile analysing tensiometers
• Surface Shear Rheology, using bicone or double-wall ring geometries on a stress-controlled rheometer.
• Imaging techniques such as AFM and SEM.
• Foam stability tests, using a foam scanner.
• Emulsion stability tests, using a Lumifuge.

For more information, please contact Leonard Sagis.