Spherical Particles, Spread Oil Layers, and Rupture of Pseudoemulsion Films

2 Spherical Particles, Spread Oil Layers, and Rupture of Pseudoemulsion Films 

If the particle also satisfies condition 4.72, then condition 4.73 implies that rupture of an oil-water-air psendoemulsion film by a spherical particle can occur if O w 90°. Such a particle will not, as we have seen, rupture symmetrical air-water-air films (for which we generally require O w 90°—but see Section 4.7). We therefore find that spherical particles that satisfy conditions 4.72 and 4.73 will promote the emergence of an oil drop into the air-water snrface withont exhibiting any antifoam behavior when used alone. If the oil satisfies condition 4.31 for formation of unstable 

Pseudo-partial wetting is also often found with both PDMS and short-chain alkane oils. However, as we have described in Section 3.6.1, in the case of such spreading on aqueous micellar surfactant solutions, equilibrium spreading coefficients are usually close to zero. This indicates that the films in equilibrium with oil lenses are relatively thick and are close to duplex in character. In turn, this means 

Another aspect of the role of particles in rupturing air-water-oil pseudoemulsion films concerns the extent to which the particles protrude from the oil-water 

FIGURE 4.82 Effect of spherical hydrophobed silica particles on stability of pseudoemulsion film formed by heptanes in saline aqueous solutions of AOT. (a) Apparatus used. Contact angles were varied by changing AOT concentration, (b) Plot of heptane drop half-life against + Bow (see text). (Aveyard, R., Clint, J.H., JCS Faraday Trans., 91, 2681, 1995. Reproduced by permission of The Royal Society of Chemistry.) 

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