Antifoam globules

The experiments show, however, that many oils with positive B and E coefficients might have low antifoam efficiency. In these cases, the stability of the asymmetric oil-water-air films is very high, and the formation of unstable oil bridges becomes impossible for kinetic reasons (factor 2 is decisive). The repulsive interaction that should be overcome for effectuation of the antifoam globules entry on the solution surface is usually termed the entry barrier. A recently... 

FIGURE 5.63 Schematic explanation of the optimal hydrophobicity of the solid particles in oil-solid antifoam compounds, (a) When an antifoam globule approaches the foam film surface, an asymmetric oil-water-air film of thickness forms, (b) The zone of contact in an enlarged scale. If the protrusion depth, dj,, of the solid particle is larger than the particle should be sufficiently hydrophobic (9 + 9o > 180°) to pierce the air-water interface and induce a film rupture however, if the particle is insufficiently hydrophobic (9 + 9q < 180°), it would stabilize the film. (c) On the other side, if the solid particle is overhydrophobized, then < PR < As and the particle is again unable to pierce the asymmetric fihn. ... 

Active Antifoam Globules Optimal Silica/Oil Ratio... 

Exhausted Antifoam Globules Silica-rich and Silica-free (both inactive) Spread Oil Layer No... 

Segregation of oil and silica into two distinct populations of antifoam globules (silica-free and silica-enriched) during storage... 

Several complementary methods were used to observe the process of foam film thiiming and destruction in the presence of antifoam globules. 

As shown in the following, the threshold value of Pc is related to a transition from one mechanism of foam destruction (rapid rupture of the foam films) to another, much slower mechanism, which includes a compression of the antifoam globules in the Gibbs-Plateau borders of the foam. 

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