ABSTRACT
This chapter introduces a number of key descriptors of foam structure, such as liquid volume fraction, bubble mono- or polydispersity or order and disorder. Understanding foam structure is a key to understanding many foam properties. The chapter provides an overview of different foam structures, emphasizing the role of bubble polydispersity and liquid fraction. The energy landscape of foam is very complex and the bubbles are generally trapped in local energy minima. In the absence of thermal fluctuations, topological changes which would be required to exit such minima do not occur spontaneously. Most of the liquid in dry foams is contained in the Plateau borders and their nodes. Films of foams in equilibrium are only some tens of nanometers thick and in structural considerations are, therefore, often approximated as having infinitesimal thickness.
