Preparation of novel silicone-based antifoams having a high defoaming performance

It is well known that the stability of the pseudoemulsion films formed on the surface of many antifoamers is important during defoaming action. We have compared, by using laser microscopic techniques, the bursting behavior of a two-dimensional pseudoemulsion film from an aqueous surfactant solution, in which four types of antifoam particles have been dispersed on a glass plate. The antifoamers used were a silicone oil, a mixed-type antifoamer (silicone oil with hydrophobic silica particles), hydrophobic silica, and a silicone-based solid antifoam (prepared by interfacial polymerization with oil and water). The pseudoemulsion film breaking was observed at a film thickness less than 0.1 mu m for both the silicone oil and the hydrophobic silica. On the other hand, the pseudoemulsion film on the top of the particles can be easily broken by convex parts of the surface for the silicone-based antifoam. Furthermore, it was discovered that the acute top of the solid particles in the mixed-type antifoam ran out of oil and broke the liquid film when the film thickness decreased to a diameter comparable to the antifoam particle (ca. 8 mu m). Based on these results, we have prepared novel silicone-based solid antifoams having a high defoaming performance by using interfacial polymerization with oil and water. These solid particles had a number of sharp-pointed needles on the surface and the roughness was estimated quantitatively as the ten point height of irregularities (R-Z) by analyzing the laser microscopic patterns. Defoaming performance was studied by monitoring the foam volume measured by the cylinder shaking test and the drum-type laundry washing machine. It was found that the defoaming efficiency was proportional to the value of R-Z, an indicator of surface roughness.