Foam Reading Answers

Foam is an entity formed by trapping pockets of gas in a liquid or solid. A bath sponge and the head on a glass of beer are examples of foams. In most foams, the volume of gas is large, with thin films separating the regions of gas. Soap foams are also known as suds. Solid foams can be closed-cell or open-cell. In closed-cell foam, the gas forms discrete pockets, each completely surrounded by the solid material. In open-cell foam, gas pockets attach to each other. A bath sponge is an example of an open-cell foam: water easily flows through the entire structure, displacing the air. A camping mat is an example of a closed-cell foam: gas pockets are sealed from

each other so the mat cannot soak up water. Foams are examples of dispersed media. In general, gas is present, so it divides into gas bubbles of diverse sizes (i.e., the material is polydisperse) separated by liquid regions that may form films, thinner and thinner when the liquid phase pipes out of the system films. When the principal

scale is small, i.e., for a very fine foam, this dispersed medium can be considered a type of colloid. 

Foam can also refer to something that is analogous to foam, such as quantum foam, polyurethane foam (foam rubber), XPS foam, polystyrene, phenolic, or many other manufactured foams. One scale is the bubble: material foams are typically disordered and have a variety of bubble sizes. At larger sizes, the study of idealised foams is closely linked to the mathematical problems of minimal surfaces and three-dimensional tessellations, also called honeycombs. The Weaire-Phelan structure is considered the best possible unit cell of a perfectly ordered foam,

while Plateau's laws describe how soap-films form structures in foams. At a lower scale than the bubble is the thickness of the film for metastable foams, which can be considered a web of unified coatings called lamellae.

Ideally, the lamellae connect in triads and radiate 120° outward from the connection points, known as Plateau borders. An even lower scale is the liquid-air interface at the surface of the film. Most of the time this interface is stabilised by a layer of amphiphilic structure, often made of surfactants, particles (Pickering emulsion), or more complex associations. Solid foams, both open-cell and closed-cell, are considered as a subclass of cellular structures. They often have deficient nodal connectivity as compared to other cellular structures like honeycombs and truss

lattices, and thus, their failure mechanism is dominated by bending of members. Low nodal connectivity and the resulting failure mechanism ultimately led to their inferior mechanical strength and stiffness compared 1 honeycombs and truss lattices,