Ross type foaming

Ross-type foaming (340) A weak solvent-solute interaction may cause surface activity. This activity, and therefore the foaminess of the solution, increases with the tendency for separation of the solution into two liquid phases. As solute concentration increases toward the critical solution point, or the plait point, foaminess increases. Once this point is reached and two phases are formed, one phase may act as a foam inhibitor and destroy the foam. 

The Ross-Miles foam behavior of 1.0 mM aqueous C12En solutions is shown in Fig. 9 [78]. It is seen that the initial foam height increases linearly with the increase in EO units, n (up to 22), but then it slightly falls for longer EO units. A similar behavior has been observed in several types of polyoxy-... 

Test Methods. Surface tension (y) measurements were taken by Wil-helmy method (25+0.1°C). Critical micelle concentrations (cmc) were obtained from Y logC curves. Contact angle. Type GI, Japan. Wetting test. Canvas disk method, CIS,HG-2-380-66. Foam test, Ross-Miles lather method. Emulslbillty was determined by mixing 20 ml of 2.5%... 

The effect of the foam film type has been discussed in Section 7.5.1. However, a question arises as to whether the Ross-Miles method can be employed in testing foams built up by the three types of foam films. The answer is given by the data presented in Fig. 7.12. 

It depicts the H(i) dependence for NaDoS foams. Curve 1 refers to common thin films, curve 2 to CBF and curve 3 to NBF. It is clearly seen that the curves differ from one another. This indicates that the Ross-Miles test can be used to distinguish foams constituted of the different types of foam films. This is in agreement with the xp(Ap) dependence for NaDoS foams (seeFig. 7.6). As mentioned in the beginning of this Section a quantitative comparison of the results by the two techniques cannot be done. 

Analogous tp(Ap) and H(x) relations were obtained for foams from non-ionic surfactants (Fig. 7.14). Here the Ross-Miles test cannot be used to distinguish foams with common thin and black films by H (the non-ionic surfactants form only one type of black films see Section 3.4). xp(Ap) dependence indicates that at low pressures (< 3103 Pa) the foam with common thin films has longer lifetime (curve 2) while in the range of higher pressures the foam with black films (curve 1) lives longer. The differences in Tp at Ap = 5-... 

Another type of foam has been observed when a multicomponent liquid has a composition close to a separation into two liquid phases. Surface tension drops to a very low value, allowing easy formation of bubbles. An example is found in solvent recovery from lubricating-oil extraction processes. This type of foam has been referred to as Ross foam,f ° named after an investigator of these foams. 

The generalization that antifoams must be present as undissolved entities has, however, occasionally been challenged [6,9,10]. A number of authors in fact report experimental results that purport to show antifoam effects due to additives that are solubilized in the foaming solution [11-13]. Thus, Ross and Haak [11], for example, identify two types of antifoam behavior associated with the effect of oils like tributyl phosphate and methyl isobutyl carbinol on the foam behavior of aqueous micellar solutions of surfactants such as sodium dodecylsulfate and sodium oleate. Wherever the oil concentration exceeds the solubility limit, emulsified drops of oil contribute to an effective antifoam action. However, it is claimed [11,14] that a weak antifoam effect is associated with the presence of such oils even when solubilized in micelles. The consequences of all this behavior are revealed if, for example, tributyl phosphate is added to micellar solutions of sodium oleate [11] at concentrations below the solubilization limit. A marked decrease in foamability is found immediately after dispersing the oil. As the oil becomes slowly solubilized, the foamability increases. However, even after the oil is completely solubilized, the foamability is still apparently less than that intrinsic to the uncontaminated surfactant solution [11]. By contrast, Arnaudov et al. [7] have more recently shown that the significant antifoam effect of n-heptanol on aqueous micellar solutions of sodium dodecylbenzene sulfonate (in the presence of NaCl) is almost completely eliminated after solubilization. 

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