Experimental Observations Concerning Contact Angles and Particle Bridging Mechanism

2 Experimental Observations Concerning Contact Angles and Particle Bridging Mechanism 

Attempts to relate the foam behavior of hydrophobic particles directly to contact angles followed more than a decade after the work of Dudenkov [150]. Of these, the first was a paper by Garrett [42], which concerned finely divided polytetrafluo-roethylene (PTFE) as antifoam material. PTFE has the merit of inertness so that any possible contribution from Marangoni spreading to the antifoam effect can be unambiguously eliminated. Moreover, reliable representative contact angles can be measured on polished PTFE plates. 

The capillary force will therefore act in a direction to cause enhanced drainage out of the foam film. The process of drainage will continue until the two three-phase contact lines at the particle surface are coincident, whereupon a hole will form in 

Particle completely dewetted to form hole in foam film 

FIG U RE 4.43 Foam film rupture caused by spherical particle with contact angle 90° 

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