Foams - Formation, formulation and properties

Foams are familiar, everyday systems, but their behavior is remarkably complex, giving them ambiguous or paradoxical properties: useful or undesirable, ephemeral or persistent, structured or disordered, fluid or rigid. A foam is generally defined as a dispersion of gases in a condensed phase, which is often an aqueous phase, but can also be an organic or metallic phase, possibly solidified. Because of their high gas content, foams have a very low density, which does not prevent them from being remarkably rigid (whipped cream foam, shaving foam), or even completely solid (metal foams, expanded polystyrene), and, where appropriate, compressible and even elastic. On the other hand, there are aqueous foams that are very rigid, yet can move easily in a pipe or against a wall, and behave like fluids depending on the stress applied.

This article describes the characteristics of surfactant-stabilized aqueous foams, the physical and physico-chemical phenomena involved throughout their life, the effect of formulation and preparation on their persistence and rheological behavior, and the main methods of study. It complements the classic texts, which focus on the physical properties of foams and the mechanical and hydrodynamic study of the thin films they contain [1][2][3][4][5][6][7][8] .