Bridging coefficient

The stability of oil bridges in foam films was studied theoretically by Garrett on the basis of the theory of capillarity. The analysis showed that a necessary condition for having an unstable bridge is that the bridging coefficient ... 

Applied Critical Capillary Pressures, Pc", and Entry, Spreading, and Bridging Coefficients for Short-Chain Alcohols (in Aqueous 2.6 mM Sodium Dodecylbenzene Sulfonate/12 mM NaCI)... 

The classic semi-initial and equilibrium entry and spreading coefficients, together with equilibrium bridging coefficients and spreading pressures, Aa w. for this system are listed in Table 4.3. Up to and including undecane, the initial and equilibrium entry coefficients are positive. For higher alkanes, they are seen to be essentially... 

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

The closer tjts to ri, the greater the ratio of T( ii) to L( it2) and the greater the probability that the phase of composition ( ii,l - ii) will be the continuous phase. For antifoam behavior within the two-phase region, it is obvious from consideration of the mode of action of antifoams that the dispersed phase should be characterized by both a tendency to emerge into the air-liquid surface of the other phase (so that F > 0) and a positive value of the bridging coefficient. 

Chaisalee et al. [125] again ascribed these effects to bridging of foam films by drops of the dispersed concentrated conjugate phase. However, measurements of the relevant bridging coefficients, although positive, are in violation of Equation 4.31. This presumably reflects experimental error. 

Joshi et al. [133] present entry, spreading, and bridging coefficients for this system, which are clearly non-equilibrium initial values (which violate Equations 3.11, 3.12, and 4.31, respectively). Direct evidence of coalescence of bubbles by bridging drops of gel phase is also presented. However, it would seem that this happens only if air-water surfaces are at nonequilibrium surface tensions, which in turn could imply negative values of the bridging coefficient under equilibrium conditions. Interestingly, Joshi et al. [133] also show that the antifoam effect diminishes markedly as the temperature is increased well above the cloud point. This effect is attributed to decreases in the bulk phase viscosity of the gel phase, rendering drops more readily deformable and more readily ejected from foam films before rupture of the relevant pseudoemulsion films. 

Denkov et al. [54] have made a detailed stndy of the role of PDMS oil in the mode of action of mixtnres of such oils with hydrophobed silica. The work concerned the effect of such an antifoam on micellar (10 mM) aqueous solutions of AOT. The chosen system was characterized by a positive initial spreading coefficient and a slightly negative equilibrium spreading coefficient for the oil on the snrfactant solntion (see Table 3.3). Both the equilibrium entry coefficient and the bridging coefficient were positive with the latter close to the limit permitted by condition 4.31. The system... 

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