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Introduction to Foams

Liquid foams

Overview

Liquid foams are made wherever gases and liquids are mixed. Ingredients such as soap help to form stable films, and therefore long-lived foams.

Foams can be made by:

  • Mixing or agitation; examples are draught beer, whipped cream and sea foam.
  • Evolution of dissolved gas; for example canned beer, soft drinks, shaving foam and hair mousse.
  • Bubbling gas through liquid.

Example of a liquid foam

(courtesy of J.J. Cilliers, UMIST)

Applications of Liquid Foam

  • Chemical processing.
  • Food products, such as whipped cream and chocolate mousse.
  • Toiletries, such as shaving foam and hair mousse.
  • Household cleaning products, such as oven cleaner and limescale remover.
  • Fire extinguishers.

Getting Rid of Liquid Foam

Industrial processes which bring gases and liquids together often form foams. These foams are generally unwanted as they can block flow or damage pumps. The petroleum and chemical processing industries are therefore interested in destroying foams. Certain chemical additives can accomplish this.

Stability of Liquid Foams

The development and stability of a liquid foam is governed by three main processes:

  • Drainage: liquid will drain through the Plateau border channels until an equilibrium state is reached.
  • Coarsening: gas diffuses between bubbles - some grow while others shrink and disappear. The net result of this process is that the average bubble size grows in time.
  • Film Rupture: if a foam film gets too thin and weak, it will rupture. Eventually the foam will collapse and vanish.