Foam One

With foams, one is dealing with a gaseous state or phase of matter in a highly dispersed condition. There is a definite relationship between the practical application of foams and colloidal chemistry. Bancroft (4) states that adopting the very flexible definition that a phase is colloidal when it is sufficiently finely divided, colloid chemistry is the chemistry of bubbles, drops, grains, filaments, and films, because in each of these cases at least one dimension of the phase is very small. This is not a truly scientific classification because a bubble has a film round it, and a film may be considered as made up of coalescing drops or grains. ... 

All aerated products are technically foams. One point of view is that aerated products are a way of making the public pay for air. This is not true in the case of many bakery products such as bread as the product is not sold by volume but by weight. The only food where this claim could be true is ice cream which is sold by volume not weight. Not only does the consumer pay for the air in ice cream as ice cream is subject to standard rate value added tax the consumer pays VAT on the air as well ... 

Brookfield, Ct., 2002, Session I, p.1-8. 27cm, 012 LOW DENSITY EXTRUDED POLYPROPYLENE FOAMS - ONE OF THE FINAL FRONTIERS Folland R Reichelt N Stadlbauer M Borealis Polymers NV Borealis GmbH (SPE,Thermoplastic Materials Foams Div. ... 

Sekisui Plastics is reported to have developed two types of heat resistant plastics foam one is PETP foam, capable of resisting temps, of up to 220C and the other is closedcell PP foam, resistant to temps, of up to 145C. Brief details are noted. 

Polyurethane sponge foam. One fabricator offers a coalescer design employing an open-celled polvure-thane foam in a horizontal tank (Fig 4). 

When the application involves foaming, one must detect both the liquid-foam interface and foam level. Radiation sensors can detect the liquid-foam interface and TDR transmitters, or conductance and RF switches can detect the foam level if it is conductive. In the case of heavier foams, vibrating or tuning-fork switches and beta-radiation gauges have been used in some cases, optical or thermal switches have also been successful. 

Among promising oligomeric foams one should also mention 2-pyranyl foams for a discussion of the chemistry, technology and properties of these materials see Finally, several works concerned with the preparation of foams from cumaron-indene and aniline-formaldehyde oligomers have been reported ... 

Nevertheless, some of the predictions of simple regular foam models are relevant to real foams. One such property is the linear modulus Go, which is the slope of the stress-strain curve at zero strain. From Eq. (9-57a), we obtain... 

When undesirable foaming of a solution cannot be reduced sufficiently by replacing the surfactant with a lower foaming one, or when the foam is caused partially or entirely by nonsurfactant components of the solution, then antifoaming agents are used to reduce the foam. Antifoaming agents act in various ways ... 

After an efficient system has been found, the main open question is how to solidify the foams. One route could be to utilise water-soluble polymers or/and polymerise water-soluble monomers. Another route could be to switch to polymeric microemulsions. One would stepwisely replace the water by the preferred polymerisable hydrophilic monomer/polymer. By doing so one can be sure that the nanostructure of microemulsion remains unaffected. The generation of the nanofoam depends on the used monomer. A fixation via irradiation with fight would be preferable, when photoactive cross-linkers are... 

To make an emulsion (foam), one needs oil (a gas), water, energy, and surfactant. The energy is needed because the interfacial area between the two phases is enlarged, hence the interfacial free energy of the system increases. The surfactant provides mechanisms to prevent the coalescence of the newly formed drops or bubbles. Moreover it lowers interfacial tension, and hence Laplace pressure [Eq. (10.7)], thereby facilitating breakup of drops or bubbles into smaller ones. 

Volume fraction of dispersed phase q>, since it determines some essential properties, such as rheological ones. For an emulsion, the value desired can mostly be predetermined by the proportions of oil and water in the recipe. This is often different for foams, especially when made by beating the value of q> obtained then depends on several conditions (see the next section). In foams one often speaks of the overrun, i.e., the percentage increase in volume due to incorporation of gas. The relation is percentage overrun = 100

[Pg.418]

Foams are very compatible even with the most sensitive formations. The reduced liquid volumes, contact time, and fluid loss make foams one of the most versatile fluids for the stimulation of shallow, sensitive formations. References 6, 22, 25, 35, and 36 illustrate improved success of production by using foamed stimulation fluids. 

Suspended solids and polymers generally tend to stabilize foams. One example is iron sulfide particles in amine solutions (26, 239, 318) also see item 7 above. In one case (107), precipitation of sodium chloride in a solvent-water separation column caused foaming. 

Two procedures described in BS4443, Part 2, 1988 [48] are suitable in particular for latex, PVC, and polyurethane foams. One is faster to carry out and can be used as a quality control method (Procedure A). Procedure B can be used to determine the load to give indentations of 25, 40, and 65% deflections and hence the sag factor can be determined. In addition, by measuring the load for specified indentations of the foam on loading (as with Procedure B), followed by measuring the indentations on unloading, a measure of the foam hysteresis can be determined. Hysteresis is a measurement of the energy absorbed by a foam when subjected to a deformation. 

Surfactants based on block copolymers of dimethylsilicone and poly(ethylene oxide) are unique in regulating the cell size in polyurethane foams. One route to such polymers used the reaction between a polysiloxane and an allyl ether of poly(ethylene oxide). 

In nanotechnology surfaces become increasingly more important because a greater fraction of the atoms are at the surfaces. In the smallest nanoparticles, all the atoms may be at the surface of the particle. This property is quite closely related to a completely different group of materials, the foams. One difference between these two situations is the local curvature of the surface. 

For a polydisperse dry foam one can define an average internal pressure P that is given by... 

Chem. Descrip. Mod. branched polyester polyol which contains no trimethylol propane based on a sat. dibasic acid and an ether glycol Uses Polyester for flexible PU foams, one-shot castables, sol n. adhesives and coatings... 

The stabilizing mechanisms displayed under these two conditions are different, and thus when dealing with food foams one has to recognize the role of the solidifying structure of the foam lamella in many important technical systems. 

Plastics — rigid polyurethane foam, expanded polyst3u-ene, honeycomb, crosslinked PVC foam (one of the most important core materials), poljnnethacrylimides, other plastics foams (excellent thermal insulation, weaker and more expensive than paper). 

---