Foams


FMN See flavin mononucleotide, foamed plastics See cellular plastics.  [c.180]

Foams are used industrially and are important in rubber preparations (foamed-latex) and in fire fighting. The foam floats as a continuous layer across the burning surface, so preventing the evolution of inflammable vapours. Foams are also used in gas absorption and in the separation of proteins from biological fluids. See anti-foaming agents.  [c.180]

The polycondensation of di-isocyanates with polyhydric alcohols gives a wide range of polyurethanes which are used as artificial rubbers and light-weight foams, and have other important properties. Isocyanates are also used as modifiers in alkyd resins.  [c.224]

R0C(0)NHR -NHC(0)-0 repeating units. The main use is in foams. See isocyanates. U.S. use 1980 933 000 tonnes.  [c.323]

Sorbitol is manufactured by the reduction of glucose in aqueous solution using hydrogen with a nickel catalyst. It is used in the manufacture of ascorbic acid (vitamin C), various surface active agents, foodstuffs, pharmaceuticals, cosmetics, dentifrices, adhesives, polyurethane foams, etc.  [c.368]

Anti-foaming agents polydimethylsiloxanes, fluorosilicones, acrylates.  [c.279]

For gear trains Protection from seizing and rapid wear Extreme-pressure and anti-wear properties Resistance to oxidation Thermal stability High viscosity Low pour point Anti-foaming properties Anti-corrosion properties  [c.284]

Performance can be illustrated for example by the time necessary for deaeration or de-emulsification of oils, anti-rust properties, copper strip corrosion test, the flash point in closed or open cup, the cloud and pour points, the foaming characteristics, etc.  [c.285]

Foaming characteristics of lubricating oils NFT 60-129 ISO/DIS 6247 ASTM D 892 Air sparging and measurement of foam after standing  [c.448]

Both separators can be built vertically of horizontally. Vertical separators are often favoured when high oil capacity and ample surge volume is required, though degassing can become a problem if liquid viscosity is high (gas bubbles have to escape against the fluid flow). Horizontal separators can handle high gas volumes and foaming crudes (as degassing occurs during cross flow rather than counter flow). In general, horizontal separators are used for high flow rates and high gas/liquid ratios.  [c.246]

There is a host of problems of practical importance that require at least a phenomenological, that is, macroscopic, view of surface physical chemistry. The contact angle (Chapter X), itself a manifestation of the thermodynamics of interfaces discussed in Chapters II and III, is of enormous importance to the flotation industry. Wetting, adhesion, detergency, emulsions, and foams all depend on the control of interfacial tensions, often through judicious use of surface active agents. These topics are covered in Chapters XII-XIV. Chapter XV takes up the now enormous subject of macromolecular surface films, including transferred Langmuir-Blodgett films, biological films and membranes. The emphasis in these chapters is on those aspects that have received sufficient attention to be somewhat established. Surface probe techniques are bringing important new molecular insight into these more applied areas of surface physical chemistry.  [c.3]

Emulsions, Foams, and Aerosols  [c.500]

In this chapter, we carry our discussion of applied surface chemistry into finely divided dispersions of liquids, vapor, or solids. Emulsions and foams are grouped together since they involve two partially miscible fluids and, usually, a surfactant. Both cases comprise a dispersion of one phase in another if both phases are liquid, the system is called an emulsion, whereas if one fluid is a gas, the system may constitute a foam or an aerosol. The dispersed system usually consists of relatively large units, that is, the size of the droplets or gas bubbles will ordinarily range upward from a few tenths of a micrometer. The systems are generally unstable with respect to separation of the two fluid phases, that is, toward breaking in the case of emulsions and collapse in the case of foams, and their degree of practical stability is largely determined by the charges and surface Aims at the interfaces.  [c.500]

Although it is hard to draw a sharp distinction, emulsions and foams are somewhat different from systems normally referred to as colloidal. Thus, whereas ordinary cream is an oil-in-water emulsion, the very fine aqueous suspension of oil droplets that results from the condensation of oily steam is essentially colloidal and is called an oil hydrosol. In this case the oil occupies only a small fraction of the volume of the system, and the particles of oil are small enough that their natural sedimentation rate is so slow that even small thermal convection currents suffice to keep them suspended for a cream, on the other hand, as also is the case for foams, the inner phase constitutes a sizable fraction of the total volume, and the system consists of a network of interfaces that are prevented from collapsing or coalescing by virtue of adsorbed films or electrical repulsions.  [c.500]

Microemulsions are treated in a separate section in this chapter. Unlike macro- or ordinary emulsions, microemulsions are generally thermodynamically stable. They constitute a distinctive type of phase, of structure unlike ordinary homogeneous bulk phases, and their study has been a source of fascination. Finally, aerosols are discussed briefly in this chapter, although the topic has major differences from those of emulsions and foams.  [c.500]

The surface tension criterion indicates that a stable emulsion should not exist with an inner phase volume fraction exceeding 0.74 (see Problem XIV-2). Actually, emulsions of some stability have been prepared with an inner phase volume fraction as high as 99% see Lissant [18]. Two possible explanations are the following. If the emulsion is very heterogeneous in particle size (note Ref. 16), may exceed 0.74 by virtue of smaller drops occupying the spaces between larger ones, and so on with successively smaller droplets. Such a system would not be an equilibrium one, of course. It appears, however, that in some cases the thin film separating two emulsion drops may have a lower surface tension than that of the bulk interfacial tension [19]. As a consequence, two approaching drops will spontaneously deform to give a flat drop-drop contact area with the drops taking on a polyhedral shape such as found in foams.  [c.504]

There appear to be two stages in the collapse of emulsions flocculation, in which some clustering of emulsion droplets takes place, and coalescence, in which the number of distinct droplets decreases (see Refs. 31-33). Coalescence rates very likely depend primarily on the film-film surface chemical repulsion and on the degree of irreversibility of film desorption, as discussed. However, if emulsions are centrifuged, a compressed polyhedral structure similar to that of foams results [32-34]—see Section XIV-8—and coalescence may now take on mechanisms more related to those operative in the thinning of foams.  [c.506]

XIV EMULSIONS, FOAMS, AND AEROSOLS  [c.518]

The situation becomes more complex in the case of a three-dimensional foam. Since the septa should all be identical, again three should meet at 120° angles to form borders or lines, and four lines should meet at a point, at the tetrahedral angle of 109°28. This was observed to be the case by Matzke [179] in his extensive statistical study of the geometric features of actual foams.  [c.521]

Intuitively, one would like the cells to consist of some single type of regular polyhedron, and one that closely meets the foregoing requirements is the pentagonal dodecahedron (a figure having 12 pentagonal sides). Matzke did find more than half of the faces in actual foams were five-sided, and about 10% of the polyhedra were pentagonal dodecahedrons. Earlier, Desch [180] reached similar conclusions.  [c.521]

The foregoing discussion leads to the question of whether actual foams do, in fact, satisfy the conditions of zero resultant force on each side, border, and comer without developing local variations in pressure in the liquid interiors of the laminas. Such pressure variations would affect the nature of foam drainage (see below) and might also have the consequence that films within a foam structure would, on draining, more quickly reach a point of instability than do isolated plane films.  [c.521]

In addition to elasticity and resilience as properties giving stability to foams, a high surface viscosity appears also to be important. While several groups found a correlation between film viscosity and foam stability [224], the addition of water-soluble polymers as thickeners slow drainage but not in proportion to their viscosity [208]. It is thought that such additives interact with the surfactant molecules to stabilize films in addition to enhancing viscosity. The size and redistribution of foam cells may also correlate with foam stability [225, 226] recent measurements of shaving cream use a dynamic light scattering technique to follow this coarsening process [227]. Reviews of foam stability and hydrophobic foams are found in Refs. 226 and 228.  [c.524]

Foam rheology has been a challenging area of research of interest for the yield behavior and stick-slip flow behavior (see the review by Kraynik [229]). Recent studies by Durian and co-workers combine simulations [230] and a dynamic light scattering technique suited to turbid systems [231], diffusing wave spectroscopy (DWS), to characterize coarsening and shear-induced rearrangements in foams. The dynamics follow stick-slip behavior similar to that found in earthquake faults and friction (see Section XU-2D).  [c.525]

The action of antifoam agents in preventing foaming can be analyzed qualitatively along lines similar to the preceding material as discussed by Ross and co-woricers [232] and by Bikerman [233]. A recent study by Wasan and co-workers [234, 235] of the antifoaming properties of oils and hydrophobic particles suggests that the antifoam drops get trapped in the Plateau borders, as illustrated in Fig. XIV-16, and destabilize the film at the borders. Shah and co-workers [236] have shown that organic ions, on the other hand, interact with surfactant to decrease the CMC, increase the area per molecule of the surfactant, and decrease the surface viscosity to reduce foam stability.  [c.525]

An important application of foams arises in foam displacement, another means to aid enhanced oil recovery. The effectiveness of various foams in displacing oil from porous media has been studied by Shah and co-workers [237, 238]. The displacement efficiency depends on numerous physicochemical variables such as surfactant chain length and temperature with the surface properties of the foaming solution being an important determinant of performance.  [c.525]

P. Becher, ed.. Encyclopedia of Emulsion Technology, Marcel Dekker, New York, 1983. J. J. Bikerman, Foams, Springer-Verlag, New York, 1973.  [c.527]

Nacconate 100 A lachrymatory liquid b.p. 25l°C. Manufactured from phosgene and 2,4-diaminotoJuene. Used for preparing polyurethane foams and other elastomers by reaction with polyhydroxy compounds. Produces skin irritation and causes allergic eczema and bronchial asthma.  [c.139]

The importance of the thin film between the mineral particle and the air bubble has been discussed in a review by Pugh and Manev [74]. In this paper, modem studies of thin films via SFA and interferometry are discussed. These film effects come into play in the stability of foams and froths. Johansson and Pugh have studied the stability of a froth with particles. Small (30-/ m), moderately hydrophobic 6c = 65°) quartz particles stabilized a froth, while more hydrophobic particles destabilized it and larger particles had less influence [75].  [c.476]

An interesting effect is that in which an A/B type of emulsion inverts to a B/A type. Generally speaking, the methods whereby inversion may be caused to take place involve introducing a condition such that the opposite type of emulsion would normally be the stable one. First, an emulsion would have to invert if exceeded 0.74, if the itmer phase consisted of uniform rigid spheres as noted in Section XIV-3A, this value of represents the point of close packing. Actual emulsion droplets are deformable, of course, and not monodisperse. Continued addition of inner phase may result in inversion, but the effect is not assured and emulsions can be made to exceed = 0.74. Emulsions greatly surpassing this value resemble biliquid foams having polyhedral cells Sebba [62, 63] has termed the unit cells of such emulsions as aphrons . An aphron may be defined generally as a phase bounded by an encapsulating soapy film [64].  [c.513]

A foam can be considered as a type of emulsion in which the inner phase is a gas, and as with emulsions, it seems necessary to have some surfactant component present to give stability. The resemblance is particularly close in the case of foams consisting of nearly spherical bubbles separated by rather thick liquid films such foams have been given the name kugelschaum by Manegold [175].  [c.519]

The second type of foam contains mostly gas phase separated by thin films or laminas. The cells are polyhedral in shape, and the foam can be thought of as a space-filling packing of more or less distorted polyhedra such foams have been called polyederschaum. They may result from a sufficient drainage of a kugelschaum or be formed directly, as in the case of a liquid of low viscosity. Again, there is a parallel with emulsions—centrifuged emulsions can consist of polyhedral cells of inner liquid separated by thin films of outer liquid. Sebba [64, 176] reports on foams that range between both extremes, which he calls microgas emulsions, that is, clusters of encapsulated gas bubbles.  [c.519]

However, the pentagonal dodecahedron gives angles that are slightly off (II6°33 between faces and 108° between lines) and, moreover, cannot fill space exactly. This problem of space filling has been discussed by Gibbs [178] and Lord Kelvin [181] the latter showed that a truncated octahedron (a figure having six square and eight hexagonal sides) would fill space exactly and, by suitable curving of the faces, give the required angles. However, experimentally, only 10% of the sides in Matzke s foams were foursided.  [c.521]


See pages that mention the term Foams : [c.15]    [c.30]    [c.38]    [c.86]    [c.89]    [c.180]    [c.261]    [c.366]    [c.374]    [c.381]    [c.391]    [c.406]    [c.414]    [c.414]    [c.310]    [c.121]    [c.506]    [c.523]    [c.523]   
See chapters in:

Encyclopedia of chemical technology volume 11  -> Foams


Engineering materials Ч.2 (1999) -- [ c.263 , c.272 ]

Plastics materials (1999) -- [ c.0 ]