When surface active molecules are present in the solution, they tend to adsorb in the gas-liquid or liquid-liquid interface. Surface active agents have hydrophobic and hydrophilic part, when at the interface, they orient so that hydrophilic part is in water-based solution and hydrophobic part in air or oil phase.
Surface active agents can be surfactant molecules, polymers, proteins or even particles. Interfacial rheology studies the response of the adsorbed interfacial layer on the deformation caused by external stimuli. The response depends on the layer composition, and interfacial rheology is thus relevant in applications where adsorbed layer plays a crucial role, like emulsions and foams and enhanced oil recovery.
How stable is your emulsion?
If you are working with emulsions, you have probably been struggling with emulsion stability. Emulsions can be stabilized with nonionic or ionic surfactants, surfactant mixtures, polymers or particles. The choice of emulsifier depends on the application. Emulsion stability can be linked to elasticity of the interfacial molecular layer. Interfacial rheology thus provides tools to study emulsion stability.
When stability is unwanted
In some applications like enhanced oil recovery or waste water treatment, the stability is unwanted as oil needs to be separated from water. In enhanced oil recovery, oil-water emulsions are stabilized by asphaltenes that are natural components of the crude oil. Asphaltenes can form very stable emulsions and thus several types of demulsification strategies have been studied.
To learn more about interfacial rheology and its relation in several different applications, listen to this recorded webinar: