Foaming

What is foaming?

Foam is gas dispersed in a liquid, with bubbles separated by thin liquid walls. Pure liquids such as water do not form stable foam, because bubbles burst as soon as they meet. Surfactants change that. They gather at the bubble surfaces and resist the thinning and rupture of the films between bubbles, partly by the Marangoni effect, in which surfactant flows toward thinning spots and restores the film.

When foam is wanted

• Personal care and hand dishwashing, where users associate foam with cleaning.
• Froth flotation, where frothers create the froth that carries minerals.
• Firefighting foams, foam cleaning on vertical surfaces, and some oilfield operations.

When foam is a problem

• Machine and industrial cleaning, including clean-in-place systems, where foam interferes with pumps and spray action.
• Spray tanks, where foam causes overflow and inaccurate mixing; see tank-mix compatibility.
• Wastewater treatment and industrial processes, where foam can overflow tanks.

Controlling foam

• Choosing low-foam surfactants, such as certain block copolymers, some nonionic surfactants and some biosurfactants.
• Defoamers and antifoams, often based on silicones, oils or hydrophobic particles, which break or prevent foam.
• Process conditions, such as temperature and agitation. Some nonionic cleaners are run near their cloud point, where they foam less.

Frequently asked questions