Bubble methods, foam production

Foams can be made by releasing a gas within a foamable liquid. For example, the opening and pouring of a bottle of soda releases pressurized CO2 gas, producing foam bubbles. Chemical reactions can also generate bubbles within the liquid. Other methods of foam production are to force both liquid and gas through a packed column (Khan et al. 1988), to spray foamable liquid onto a screen on which a fan is blowing (Aubert et al. 1986), or to use the foam-extrusion process (Han 1981). 

Method. Figure 3 shows the equipment used by us for loading a culture medium with radon and decay products. Air was circulated in a closed system, driven by a membran pump (MP). The system consisted of a Ra-226 solution (Ra), a security bubble flask with water (H20), a membran bacteria filter (MF) and a second bubble flask containing 100 ml RPMI 1640 culture medium (CM). This medium contains 100 IE/ml penicilin and streptomycin and 0.75% L-glutamin. Foetal calf serum, an essential part of blood cultures, must not be added, else the airstream would develop foam. Furthermore we added a small amount of Pb(N03)2 and Bi(N03)2, about 10 ng of each, as "carriers" for the radon decay products to avoid a "wall effect". 

Olefins or alkenes are defined as unsaturated aliphatic hydrocarbons. Ethylene and propylene are the main monomers for polyolefin foams, but dienes such as polyisoprene should also be included. The copolymers of ethylene and propylene (PP) will be included, but not polyvinyl chloride (PVC), which is usually treated as a separate polymer class. The majority of these foams have densities <100 kg m, and their microstructure consists of closed, polygonal cells with thin faces (Figure la). The review will not consider structural foam injection mouldings of PP, which have solid skins and cores of density in the range 400 to 700 kg m, and have distinct production methods and properties (456). The microstructure of these foams consists of isolated gas bubbles, often elongated by the flow of thermoplastic. However, elastomeric and microcellular foams of relative density in the range 0.3 to 0.5, which also have isolated spherical bubbles (Figure lb), will be included. The relative density of a foam is defined as the foam density divided by the polymer density. It is the inverse of the expansion ratio . 

Aubertein and Emeury [29] made a detailed examination of the causes of foaming. Oxidation of non-sulphonated resorcinol is the original cause of gas evolution during nitration. When the product is in the form of very fine crystals the gas bubbles attach themselves to the crystals and raise the product to die surface in the form of a foam. This does not occur when the crystals of die product are large. Therefore, die method of nitration should be such as to favour formation of large ctystals of styphnic acid. To achieve this, Aubertein and Emeuty advise ... 

Therefore, the technological challenge is large, particularly in the case of particle mixtures with near similar physical properties such as size and size distribution, density and morphology. Then, differences in surface chemistry can be exploited to separate the particles,for instance via flotation [33],L-L interfacial partitioning [34-36], foam and gas aphrons (stabilised micro-bubbles) fractionation, and electrophoretic and electrostatic techniques. This whole field, despite its maturity in other industries such as metallurgy and solid waste fractionation, is totally imderdeveloped for fine-chemical and biotechnological production methods. 

Hydrosilylation proved to be an effective method of end-linking this type of elastomer but a side reaction which consumes SiH functionality and generates gaseous by-products caused complications. Among these were a tendency to foam or bubble and a need to use an excess of SiH functional end-linker for optimum properties. The use of HNMR proved to be an effective tool to trace end linking and side reactions. When the side reactions were taken into account the recursive method was effective in predicting molecular weights, gel... 

Whether the bubbles are spherical, polyhedral, or in between, they typically have a distribution of sizes and pack together into a disordered, aperiodic structure. In Fig. 18.1 the average bubble diameter is 2 mm, but similar structures are also found in foams where the average bubble diameter is varied from 10 p,m to 1 cm. In practice, the average bubble size and shape in a foam can be altered for a given liquid according to the production method, the surface-active ingredients, and other chemical additives such as viscosity modifiers or polymeric stabilizers. 

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