Soft Matter: Controlling emulsions and foams through interactions between drops and bubbles - from food to minerals processing

Project Leader: Ray Dagastine
Collaborators: Franz Grieser (Chemistry), Derek Chan (Mathematics), Rico Tabor (Monash University)
Sponsors: Australian Research Council, Melbourne School of Engineering
Primary Contact: Ray Dagastine (
Keywords: Complex Fluids; Drops and Bubbles; fluid dynamics; Nanofabrication; Soft Matter; Surface Forces
Disciplines: Chemical & Biomolecular Engineering
Domains: Convergence of engineering and IT with the life sciences
Research Centre: Particulate Fluids Processing Centre (PFPC)


The dynamic interfacial forces in soft matter materials (e.g. drops, bubbles, and even biological cells) mediate or control macroscopic behaviour in growing the high-value sectors of biotechnology and nanotechnology as well as in materials used in everyday items.  Some examples include the production of salad dressing, milk and shampoo, industrial processes such as solvent extraction used for pharmaceutical and mineral purification, as well as, development of microfluidic devices for new applications.  The addition of surfactants, polymers and biological molecules, at these interfaces impart a multilevel complexity and lateral heterogeneity starting at the molecular scale and spanning to the macroscopic scale.  This complexity often creates a gap in our understanding of how these molecular structures mediate dynamic interfacial forces on the nanoscale and the material behaviour on a large scale.  To go forward in the processing and control of soft matter, studies must focus on soft matter interfaces with the complexity of real world systems to push the boundaries of our understanding of soft matter systems to new levels.  This requires careful selection of interfaces with growing degrees of complexity and innovative approaches that link nanoscale interfacial forces to macroscopic behaviour.

Two Phase Flow and TransportQuestions on the fluid flow in two phases systems (i.e. two liquids or a liquid and a gas) and the transport of molecules to the interface between these phases is becoming more and more important as microfluidic devices as well as in minerals processing equipment such as froth floatation and solvent extraction. Atomic Force Microscopy measurements can be used to probe the fluid flow between drops or bubbles when materials are adsorbed in equilibrium with solution or with slow adsorption dynamics. To examine the adsorption behaviour of bubbles or drops just after forming is more challenging. Methods including dynamic interfacial tension can be used.  One other approach is to examine bubble or drop rising in a column and examine the acceleration or deceleration under buoyant flow as a function of solution additive. This can be used to probe very fundamental questions as well as more applied questions on how a bubble or drop propagates through solution with more complex or structured additives (e.g. polymers or polyelectrolytes added in solution during froth floatation). This project provides a flexible platform to probe a large range of systems and studies from this project will interface well with AFM interaction studies and bulk emulsion and foam studies.

Interfacial heterogeneity of emulsion droplets: The adsorption of surfactants, polymer and biological macromolecules, (proteins, polysaccharides, lipids, fatty acids, etc.) onto droplets or bubbles can often cross link to form networks larger than the molecular scale.  This interfacial heterogeneity both parallel and normal to the interface gives the interface both elasticity and viscosity in response to perturbations from any type of deformation of the droplets or bubbles. This interfacial behaviour is a result of collective processes in a network of molecules across the interface. On a macroscopic scale, these phenomena are described as the interfacial rheology of the material. A number of techniques employ macroscopic perturbations including oscillating bubbles or drops, film pressure methods, and more novel approaches such as using a magnetic shear bar without a direct link to the nanoscale.  This project will focus on developing new methods to study interfacial rheology using atomic force microscopy and link these studies to larger scale stability and rheology behaviour of emulsions for applications in foods, personal care products and minerals processing.

Further information:

Controlled collKey nanoscale interations of drops, particles and bubbles