Understanding the mechanisms that lead to desired foam properties

Foams have numerous applications in our daily life – from food like for example milk foam, ice cream or beer foam to soap foams in hygiene or cleaning to packaging materials. From our daily experience we know that some foams are more stable than others. But why is it like that? Which molecular properties influence the stability of the foam? Foams are produced by lowering the surface tension of the air/water interface. This is accomplished by adding surface active molecules. Proteins are good foaming agents since they show high foamability. Nevertheless, the composition and the intermolecular interactions at the interface are of crucial importance for the properties of the resulting foam. For example adding carbohydrates to the protein solution in many cases enhances the stability of the resulting foam.  Moreover, foams are characterized on different length scales – from the arrangement of the gas bubbles on a macroscopic scale over the composition and thickness of the lamella on a mesoscopic scale to the characterization of the molecules on a microscopic scale. By investigating foams on different length scales structure-function relationships that connect the molecular level with the macroscopic foam properties can be understood. With this knowledge it will be possible to produce foams of desired macroscopic properties like e.g. a high stability of the resulting foam. Techniques used for these studies include, among others, microscopy and surface-specific sum-frequency generation spectroscopy.