High-stability foams

G.S. Styler, J.W. Lane, R.H., High-Stability Foams for Long-Term Suppression of Hydrocarbon Vapors in Proc., SPE Annual Technical Conference, Society of Petroleum Engineers Richardson, TX, 1996, SPE paper 36616. 

These high stability foams correlate directly with the results based upon interfacial tension gradient measurements, confirming the significance of Marangoni phenomena (31) in three phase foam stability. 

K.S. (1995) High-stability foams for long-term suppression of hydrocarbon vapours, US Patent 5,434,192, Jul, 18, 1995. 

The dynamic foam stability is usually measured by the volume of foam at a specific equilibrium flow rate, while the static foam stability is measured by the rate of collapse. Dynamic measurements are particular relevant for transient foams, while for foams of high stability, the static or equilibrium methods are usually more useful, particular for highly stabilized foams such as protein-stabilized foam systems. 

Use of Highly Stabilized High-Expansion Foams in Fighting Forest Fires... 

We have recently developed and obtained a patent for an ultra-stabilized high expansion foam (5 ) with expansion and drainage characteristics as shown in Table VI, using a polymeric additive for stabilization without harming expansion. 

Foam properties related to salt. The addition of sodium chloride to soybean protein suspensions caused them to form high-capacity, low-stability foams (13). It was suggested that foam capacity increased because salt improved protein solubility at the interface of the colloidal suspension during foam formation, but retarded the partial denaturation of the surface polypeptides of proteins that are necessary for protein-protein interaction and stability. 

The values of Q obtained from the best fit of Eq. (3.115) (the solid lines in Fig. 3.95) to the experimental data (the circles in Fig. 3.95) assuming Cc = Ce are (1.93 0.04)-10 9 J for temperatures lower than 23°C and (8.03 0.19)-10 2° J for temperatures higher than 23°C. The possible error arising from the assumption that Cc = Ce is analysed elsewhere [384] it can raise the Q value by up to 20%. The good fit of the experimental results to the theoretical dependence and the high stability of the foam bilayers with respect to their rupture even under a-particle irradiation, show that in the case of DMPC bilayers the assumption Cc = Ce is probably accurate. 

All this reveals that in order to explain the principle difference between foams of high and low stability, other more powerful factors should be involved. The latter enhance the formation of highly stable foams (in effect, with unlimited stability) with respect to coalescence. 

The study of a large number of various surfactants in aqueous and non-aqueous media has shown that a sharp transition towards films of high stability at increasing surfactant concentrations is always related to the appearance of black spots in the microscopic films [17,42,43]. It was established that the surfactant concentration corresponding to black spot formation lies in the range of sharp increase in the dependence foam lifetime x on surfactant concentration C. 

The data in Tables 7.7 and 7.8 reveal that most significant raise in the stability of the foamed emulsions is observed when the volume of the organic phase increases to a value that provides a concentrated foamed emulsion with droplets of polyhedral shape. In such an emulsion the gas remains longer due to the strong delay of its diffusion and to the high stability of the droplets towards coalescence. 

The systematic study of foam bilayers from phospholipids [28,38-40] reveals that they do not rupture spontaneously at any concentration allowing their formation. That is why in the case of phospholipid foam bilayer the dependence of their mean lifetime on the bulk amphiphile concentration cannot be measured in contrast to foam bilayer from common surfactants [41,42], This infinite stability of phospholipid foam bilayers is the cause for the steep W(d) and W(C) dependences. In the case of AF foam bilayers this high stability was confirmed by a very sensitive method [19,43] consisting of a-particle irradiation of foam bilayers. As discussed in Sections 2.1.6 and 3.4.2.2, the a-particle irradiation substantially shortens the mean lifetime of foam bilayers. The experiments showed that at all temperatures and dilutions studied (even at d,), the foam bilayers from AF did not rupture even at the highest intensity of irradiation applied, 700 (iCi. 

The thinnest-black films have been found to play a particularly important role in the formation of highly stable foams. They are used as models in the study of surface phenomena at various interfaces, molecular interactions between two contacting phases at short distances, including at bilayer contact. This fact in itself is of the utmost importance in studying the formation and stability of concentrated disperse systems and in modelling the contact between the two biomembranes. For this reason the book discusses different aspects of black foam films and some intriguing perspectives for future development, for instance, as a self-organising nanomolecular system, have been pointed out. 

Foams are dispersions of gas in a relatively small amount of liquid. When they are still on the surface of the which they were formed, they also are called froths. Bubbles range in size from about 50 fim to several mm. The data of Table 20.1 show densities of water/air foams to range from 0.8 to 24g/L. Some dissolved or finely divided substances may concentrate on the bubble surfaces. Beer froth, for instance, has been found to contain 73% protein and 10% water. Surface active substances attach themselves to dissolved materials and accumulate in the bubbles whose formation they facilitate and stabilize. Foam separation is most effective for removal of small contents of dissolved impurities. In the treatment of waste waters for instance, impurities may be reduced from a content measured in parts per million to one measured in parts per billion. High contents of suspended solids or liquids are removed selectively from suspension by a process of froth flotation. 

Flame Retardance. The most important reason for phenolic foam being an excellent flame retarder is that the phenolic polymer is easily carbonized and the char part formed as a result is highly stabilized. This mechanism of char-formation is considered that of a multi-aromatic ring with chemically stabilized strong bond formed through a dehydrogenation reaction by heating and oxidation. 

Water. Caution account for the buildup of trace amounts of other species salts may precipitate if the concentration of salts becomes too high. Increased corrosion can occur because the recycle causes the buildup of unexpected species that enhance corrosion. Trace surfactants can build up and stabilize foams, causing foaming in distillation and stable emulsions in decanters. Although the buildup of trace species can be controlled by purging or by separation, the location of the purge stream can affect the overall performance. Purging minimizes but does not eliminate waste. 

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