Neat Polydimethylsiloxane Oils

Comparison of Applied Critical Capillary Pressures Entry Spreadings and Bridging Coefficients with Foam Behavior for Neat Polydimethylsiloxane Oils with Various Surfactant Solutions 

commercial Ci2/i4(glucopyranoside)i2 Ci2E025S04Na, commercial sodium dodecyl-polyoxyethylene-3-sulfate C12APB, commercial dodecyl amino-propyl betaine. 

8 Also contains -81 mM ionic strength simple electrolyte impurities. 

We find then that the similarities in antifoam behavior of neat oils represented by alcohols, alkanes, and PDMSs are rather more obvious than the differences. In all cases, it would seem that the dominant factor is the magnitude of the critical capillary pressure required to rupture the relevant pseudoemulsion films. The high stability of that film means that oil drops are readily removed from foam films before causing any rupture. It is the application of increasing capillary pressures upon drops trapped in Plateau borders during foam drainage that causes rupture of the relevant pseudoemulsion films. However, the actual mode of foam film rupture by drops, which then enter the air-water surface, is not well understood. 

2 Antifoam Effects of Neat Oifs in Non-Aqueous Foaming Systems 

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FIGURE 6.2 Deactivation of antifoam effect of polydimethylsiloxane oil alone. Polydimethylsiloxane, of viscosity 50 mPa s, was added neat to solution of 5 x 10" M sodium nonyl benzene sulfonate in 3 x 10 M NaCl. (a) Volume of air in foam generated by shaking 0.025 dm of a surfactant solution containing 0.63 g dm" of the oil in a 0.1 dm measuring cylinder—each cycle consisting of 30 shakes, (b) Effect of several shake cycles on drop size distribution of the oil (by Malvern Sizer). (After Yorke, J.W.H., unpublished work.)... 

Not only must coalescence be involved in the antifoam deactivation process but it must obviously also be involved in the reactivation of deactivated antifoam dispersion by addition of fresh polydimethylsiloxane oil. Here the effectiveness of the added oil has been shown to decrease with decreasing drop size, being most effective if neat oil is simply added to the deactivated dispersion. It is obvious that this effect must concern the efficiency of the coalescence of neat oil drops with silica-rich, but... 

We have reviewed the antifoam behavior in aqueous surfactant solution of neat oils represented by short-chain alcohols, alkanes, and polydimethylsiloxanes, all... 

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