*Carrier – usually an oil that is insoluble in the foaming medium. Oils have low surface tensions and migrate to the air/liquid interface. It may be vegetable oil, mineral oil, or silicone based.
*Hydrophobe – finely divided solids that move with the carrier across the surface and physically disrupt bubble walls.
*Surfactants – used to prepare stable emulsions of the carrier in the diluents. Also act in spreading and dispersing the antifoam in the foaming medium. Selection of the surfactant package is often key to a successful antifoam formulation.
*Diluent – usually water. Antifoams and defoamers are effective at low doses (often less than 0.01%) so stable dilutions allow better dosing control resulting in cost savings for the user.
How do antifoams work?
_ While 95% of all foam problems occur in aqueous media, pure water does not foam. The addition of surfactants and other surface-active chemicals trap air at the liquid surface causing foam to build-up.
_ A defoamer or antifoam must be insoluble in the foaming media and have a low surface tension so it spreads across the foam surface.
_ Higher dispersibility results in quicker knockdown but may reduce hold-down.
How can I select the best antifoam for my application?
_ What's foaming
_ What's the process stream
_ Any agitation
_ How will the antifoam be applied
_ Temperature, pH
_ Operating and regulatory limitations