Relative Effectiveness of Antifoam Entities and Foam Structure

4 Relative Effectiveness of Antifoam Entities and Foam Structure 

Equation 5.16 implies that the chance of the Plateau border capillary pressure at the top of the foam column exceeding the critical capillary pressure for emergence of antifoam entities into air-water surfaces (and in consequence for foam film rupture) therefore increases with increasing foam height in the case of an equilibrium foam. In principle, this could mean that a given antifoam dispersion will be totally 

We now explore whether we can provide a theoretical basis, using a physical model, for the phenomenology described here. 

These considerations suggest that antifoam action should have some of the aspects of a stochastic process. Such an approach has therefore been adopted by Garrett [1]. Here we outline that theory but include a number of significant modifications in order to take account of recent developments in the relevant science. The basis of the theory is an expression for the probability of a bubble surviving despite having several antifoam entities associated with it. Thus, if the probability of each antifoam entity in a dispersion of antifoam species i being ineffective is and there are Ni(r such entities associated with a given bubble of equivalent spherical radius r.  

FIGURE 5.6 Foam generated by shaking 0.05 dm solution in a 0.25 dm graduated glass cylinder for 15 s. (a) 0.01 M aqueous sodium dodecyl sulfate solution— volume of air in foam -0.27 dm (b) 0.01 M aqueous sodium dodecyl sulfate with 2 g dm of PTFE powder [25] of particle size range 5-10 microns— volume of air in foam -0.17 dm representing a reduction of -38% due to the antifoam action of the PTFE [24]. Size bars, 0.1 dm. 

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