Aqueous foams are commonly used in multiple applications, such as food, cosmetics, and oil production. Foamability (ability to generate foams) and foam stability (ability to maintain original foam structure) are generally used to describe the foaming properties of various surfactants and gases. This work presents a novel method for testing and characterizing foamability and stability for all kinds of liquid foams using a vibrating viscometer. The procedure of the method developed consists of introducing a gas into a surfactant solution through a sintered glass frit at a constant flow rate contained in a cylindrical glass column. The apparent viscosity of the fine foams generated is recorded with time using a vibrating viscometer. Two novel parameters have been derived from the measurements of the changes in the foam viscosity. The initial foam viscosity is used to represent the foamability and the rate of viscosity decreasing with time is used to represent foam stability. These parameters enable one to distinguish two different stages (dominated respectively by drainage and coalescence) of the foam decay, and on their basis the foam stability can be predicted, irrespective of whether constituting an unstable (wet) or a (meta)stable (dry) foam system. The validity of the method elaborated is demonstrated by applying various unstable and stable foam systems using different gases (e.g., air, N<sub>2</sub>, and CO<sub>2</sub>) and surfactants from anionic, cationic, zwitterionic, and nonionic classes. This method is also employed to study the effects of nanoparticles on the foamability and stability of aqueous foams. The viscosity effect that is against gravity drainage and the jamming effect that prevents bubble coalescence induced by nanoparticles are well interpreted using this method. The methods and parameters elaborated enable one to distinguish the stability of foam systems based on swift and comparatively short measurements.

Novel method for testing and characterizing foamability and foam stability using a vibrating viscometer

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