Solubilised Chemicals that Cause Antifoaming

Solubilised antifoamers such as tributyl phosphate and methyl isobutyl carbinol, when added to surfactant solutions such as sodium dodecyl sulphate and sodium oleate, reduce foam formation [27]. In cases where the oils exceed the solubility limit, the emulsifier droplets of oil can greatly influence the antifoam action. It has been claimed [27] that the oil solubilised in the micelle causes a weak defoaming action. Mixed micelle formation with extremely low concentrations of surfactant may explain the actions of insoluble fatty acid esters, alkyl phosphate esters and alkyl amines. 

Droplets and Oil Lenses that Cause Antifoaming and Defoaming 

Undissolved oil droplets form in the surface of the film and this can lead to film rupture. Several examples of oils may be used Alkyl phosphates, diols, fatty acid esters and silicone oils [poly(dimethyl siloxane)]. 

A widely accepted mechanism for the antifoaming action of oils considers two steps The oil drops enter the air/water interface, and the oil then spreads over the film, causing rupture. 

The antifoaming action can be rationalised [28] in terms of the balance between the entering coefficient E and the Harkins [29] spreading coefficient S, which are given by the following equations. 

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