Gas-foaming

Another approach to use gas as a porogen has been recently developed. The method involves both gas foaming and particulate leaching. The latter method is preferred because it does not result in the creation of a nonporous outer skin. 

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Rheology. The rheology of foam is striking it simultaneously shares the hallmark rheological properties of soHds, Hquids, and gases. Like an ordinary soHd, foams have a finite shear modulus and respond elastically to a small shear stress. However, if the appHed stress is increased beyond the yield stress, the foam flows like a viscous Hquid. In addition, because they contain a large volume fraction of gas, foams are quite compressible, like gases. Thus foams defy classification as soHd, Hquid, or vapor, and their mechanical response to external forces can be very complex. 

Other Octoate Uses. Metal octoates are also used as driers in printing inks. Another appHcation of octoates includes the use of the aluminum salt to gel paint. Stannous, dibutyltin, and bismuth carboxylates find appHcation as catalysts in polyurethane foam appHcations in order to obtain a reaction efficiency suitable for industrial production. In polyurethane foam manufacture the relative rate of polymeriza tion and gas foaming reactions must be controlled so that the setting of the polymer coincides with the maximum expansion of the foam. 

On the night before and early morning of the accident, a series of human and technical errors caused the water for flushing pipes to pass through several open valves and flow into the MIC tank. The w ater and MIC reacted to produce a hot and highly pressurized gas, foam, and liquid, that... 

Waste gas from produced hydrocarbons can be safely disposed by reinjecting into a formation. The waste gas is mixed with a surfactant to form a foam that, in turn, is placed within a disposal zone of a subterranean formation. The waste gas is trapped within the foam, thereby reducing the mobility of the gas in the formation, which, in turn, restricts the ability of the waste gas to readily flow out of the disposal zone and into the producing zone of the formation. The waste gas foam can be placed into the formation by coinjecting the surfactant and the waste gas, or it can be formed in situ by first injecting the surfactant and then injecting the waste gas [1356]. 

An interface is defined as a boundary between two phases. The solid/liquid and the liquid/liquid interfaces are of primary interest in suspensions and emulsion, respectively. Other types of interfaces such as liquid/gas (foams) or solid/gas interfaces also play a major role in certain pharmaceutical dosage forms, e.g., aerosols. 

PP bead foams were subjected to oblique impacts, in which the material was compressed and sheared. This strain combination could occur when a cycle helmet hit a road surface. The results were compared with simple shear tests at low strain rates and to uniaxial compressive tests at impact strain rates. The observed shear hardening was greatest when there was no imposed density increase and practically zero when the angle of impact was less than 15 degrees. The shear hardening appeared to be a unique function of the main tensile extension ratio and was a polymer contribution, whereas the volumetric hardening was due to the isothermal compression of the cell gas. Foam material models for finite element analysis needed to be reformulated to consider the physics of the hardening mechanisms, so their predictions were reliable for foam impacts in which shear occurred. 16 refs. 

DIRECT GAS FOAMING GIVES PP A PERFORMANCE EDGE OVER EPS... 

Only 10% to 30% of the pores were interconnected in the gas foaming process. Nonwoven fiber meshes exhibited poor mechanical integrity. Mass transport of... 

Liquid gas foam lather, whipped cream, foam on beer... 

A foam is a dispersion of a gas in a liquid or a solid medium. Some properties of foams resemble those of emulsions, which is not surprising because a foam can be thought of as an emulsion in which the dispersed phase is a gas. Foams are, to our knowledge, never thermodynamically stable, they can only be kinetically trapped. This may be one reason why a quantitative description of foams is only poorly developed. Very good introductions into the subject are Refs. [564-566],... 

Harris, P.C. A Comparison of Mixed Gas Foams With N2 and C02 Foam Fracturing Fluids on a Flow Loop Viscometer in Proc., Annual Technical Conference of SPE Society of Petroleum Engineers New Orleans, LA,... 

The adsorption mechanisms of surfactant at interfaces have been extensively studied in order to understand their performance in many processes such as dispersion, coating, emulsification, foaming and detergency. These interfaces are liquid-gas (foaming), liquid-liquid (emulsification) and liquid-solid (dispersion, coating and detergency). 

Viscous Pressure Drop. For continuous bubble trains with perfectly mobile interfaces moving through a given Dm channel, the dynamic pressure drop in the gas (foam) phase over a single tube segment D follows from Equation 16 ... 

This result indicates that the gas (foam) permeability increases with capillary number and average bubble size. Also, k varies with... 

Figure 9. Observed dependence of gas (foam) permeability on gas flow rate for low liquid rates. The data shown correspond to different displacement histories and A for gas only displacements with the pressure being increased between each test for gas only displacement, but with the pressure being lowered and O to Ql = 0.3 jjJL/s and the pressure being increased.

Qg)b volumetric gas (foam) flow rate through the Dm channels Qg gas flow rate... 

Defoaming is the operation by which foam is removed. Foam is the dispersion of a gas in a iiquid where the distances between individuai bubbies are very smaii. in a foam system, the voiume ratio of gas to iiquid is very high and the buik density approaches that of a gas. Foam can cause probiems in anaiyticai operations such as chromatographic separation and moiecuiar spectrometric detection. 

Whipped cream, soap suds Liquid Gas Foam... 

Liquid Gas Foam Whipped cream, beaten egg whites... 

Nam YS, Yoon JJ, Park TG. A novel fabrication method of macroporous biodegradable polymer scaffolds using gas foaming salt as a porogen additive. J Biomed Mater Res 2000 53. 

Plasmid DNA has also been incorporated into PLGA copolymer matrices using gas foaming (137). The incorporation efficiency of the DNA... 

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