Melting of Hydrophobic Particles and Antifoam Behavior

Certain hydrophobic materials that exhibit antifoam effects have melting points at temperatures 100°C. Examples include hydrocarbon waxes, triglycerides, and long-chain fatty acids. 

The most striking feature of the behavior of n-docosane is the sharp deterioration of antifoam effect in the region of the melting point at 44 C. An extremely pure sample was used, and therefore a sharp melting transition was observed. Similar observations have been made by Aronson [37] for hydrocarbons and fatty acids in solutions of sodium tridecylbenzene sulfonate. 

FIGURE 4.68 Effect of temperature on antifoam behavior of finely divided hydrocarbons [1.2 g dm 3 hydrocarbon in aqueous 0.5 g dm commercial sodium alkyl (C,o, 4) benzene sulfonate solution]. (After Garrett, P.R., Mode of action of antifoams, in Defoaming, Theory and Industrial Applications, Garrett, P.R., ed., Marcel Dekker, New York, Chpt 1, p 1, 1993 Davis, J., Garrett, P.R. unpublished work.) 

That antifoam effects may be associated with solid wax or fatty acid particles is not altogether surprising. Under microscopic observation, the particles are observed to exhibit more irregular shapes than the emulsion spheres from which they are 

That the liquid hydrophobic oils formed above their respective melting temperatures are ineffective is a consequence of the metastability of the relevant pseudoemulsion films, as we have discussed elsewhere (see, e.g.. Section 3.3). In the case of the impure materials where a region of mixed solid and liquid phase exists, it seems likely that the solid component is able to destabilize those films. Similar effects have been described in oil-in-water emulsion systems where partial melting leads to instability of the oil-water-oil films due the presence of crystals at the oil-water surface [204-206]. We address the effect of particle destabilization of pseudoemulsion films on antifoam action in the following section. 

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