Many dynamic processes that generate bubbles are nonlinear, many exhibiting mathematically chaotic patterns consistent with chaos theory. In such cases, chaotic bubbles can be said to occur. In most systems they arise out of a forcing pressure that encounters some kind of resistance or shear factor, but the details vary depending on the particular context.
The most widely known example is bubbles in various forms of liquid. Although there may have been an earlier use of the term, it was used in 1987 specifically in connection with a model of the motion of a single bubble in a fluid subject to periodically driven pressure oscillations (Smereka, Birnir, and Banerjee, 1987). For an overview of models of single-bubble dynamics see Feng and Leal (1997). There is extensive literature on nonlinear analysis of the dynamics of bubbles in liquids, with important contributions from Werner Lauterborn (1976). Lauterborn and Cramer (1981) also applied chaos theory to acoustics, in which bubble dynamics play a crucial part. This includes analysis of chaotic dynamics in an acoustic cavitation bubble field in a liquid (Lauterborn, Holzfuss, and Bilio, 1994). The study of the role of shear stresses in non-Newtonian fluids has been done by Li, Mouline, Choplin, and Midoux (1997).
A somewhat related field, the study of controlling such chaotic bubble dynamics (control of chaos), converts them to periodic oscillations, and has an important application to gas–solids in fluidized bed reactors, also applicable to the ammoxidation of propylene to acrylonitrile (Kaart, Schouten, and van den Bleek, 1999). Sarnobat et al.) study the behavior of electrostatic fields on chaotic bubbling in attempt to control the chaos into a lower order periodicity.
An early attempted application that led to failure was in Alan H. Guth’s (1981) chaotic inflation theory of the early period of the universe. While he did not precisely use the term “chaotic bubbles,” his model involved “bubbles” in the original cosmic foam that collided chaotically. The model has since been modified due to the inability to find in the real universe some of the phenomena predicted by it, with improvements involving quantum fluctuations provided by Andrei Linde (1986).
In economics, bubbles are due to speculation in asset markets, causing an economic bubble. The first to apply the term in this context was J. Barkley Rosser, Jr. in 1991. While they did not use the term, Richard H. Day and Weihong Huang (1990) showed that the interaction of fundamentalist and trend-chasing traders could lead to chaotic dynamics in the price path of a speculative bubble. De Grauwe, Dewachter, and Embrechts (1983) applied such a model to foreign exchange rate dynamics.
Foam is an object 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 of liquid or solid 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 connect 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 different sizes (i.e., the material is polydisperse)—separated by liquid regions that may form films, thinner and thinner when the liquid phase drains 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.