Solidifying foams

Ice cream is simultaneously both an emulsion and a partially solidified foam, so it comprises three phases at once. The ice cream would be too solid to eat without the air, and too cold to eat without discomfort. The air helps impart a smooth, creamy consistency. The solid structure is held together with a network of globules of emulsified fat and small ice crystals (where small in this context means about 50 xm diameter). 

This description corresponds to the case of disperse structures of globular type in which the strength originates from a continuous skeleton that forms due to adhesion of individual particles upon the conversion of free disperse system into structured disperse system. There are, however, other types of structures, such as, e.g., cellular structures (in solidified foams and emulsions), in which the skeleton consists of continuous films of solid-like dispersion medium. Such structures, typical for some polymeric systems, may... 

Elastic deformation also reveals itself in foams and concentrated emulsions. The shear stress in this case is determined by an increase in the interfacial area due to the deformation of the system. Mechanical properties of solidified foams and other solid-like cellular structures are governed by the degree of dispersion, type of backbone structure and a combination of mechanical characteristics of dispersed phase and dispersion medium. 

Elastic deformation can also be observed in foams and concentrated emulsions. In such cases, the yield stress is determined by the increase in the interfacial area upon the deformation of the particles. The mechanical properties of solidified foams and other solid-like materials with a cellular structure are defined by the degree of their dispersion, their backbone structure, and the combination of the mechanical properties of dispersion medium and dispersed phase. 

This description holds true for disperse systems of the globular type, in which a continuous backbone is formed due to the cohesion of the individual particles in the course of transformation of a free disperse system into a connected disperse system. In such systems, the backbone formed is the main carrier of the strength. At the same time, there are also other types of systems, for example, those with a cellular structure (solidified foams or emulsions). Such structures are typical in polymeric systems and may form in the course of new phase formations by condensation in mixtures of polymers. An individual approach also needs to be employed in the description of the mechanical properties of structures with anisometric particles, due to the specifics of the cohesive forces in such systems. In addition to porous structures, we also consider various compact microheterogeneous structures, such as mineral rocks, modern composite materials, and natural materials such as bone and wood. 

In another variation of the process, the foaming mix is fed to the bottom of a cylinder and the foaming mixture is pushed upwards (the Vertifoam process). The mass of material above the reacting foam can be used to control density, whilst in addition volatiles and gases find it more difficult to escape from the system. The solidified cylinder of foam may then be sliced horizontally into large discs. 

Thirdly, a stable icing foam requires a tendency for the surface of the extended protein film to solidify, thereby giving structure and permanence to the foam. Egg albumen is a hydrophilic (water-loving) colloid, for it is readily soluble in water. However, when subjected to heat, egg albumen becomes insoluble in water or is said to be hydrophobic (water-hating). Through this phenomenon of changing solubility, egg whites make very stable foams if used at sufficient concentration. 

Surface films much more viscous than the bulk of the material occur also at a constant temperature. Thus, proteins denature at interfaces and produce interfacial films. Evaporation of the solvent into the atmosphere leaves a layer of higher concentration on the surface of the solution. As, usually, higher concentration means higher viscosity, a viscous surface film results. Again, the loss of solvent may be so great that the films solidify and a solid foam of an indefinite persistence is obtained. As a first approximation, the foam on milk consists of evaporated milk. 

To be semisolid, a system must have a three-dimensional structure that is sufficient to impart solidlike character to the undistributed system that is easily broken down and realigned under an applied force. The semisolid systems used pharmaceutically include ointments and solidified w/o emulsion variants thereof, pastes, o/w creams with solidified internal phases, o/w creams with fluid internal phases, gels, and rigid foams. The natures of the underlying structures differ remarkably across all these systems, but all share the property that their structures are easily broken down, rearranged, and reformed. Only to the extent that one understands the structural sources of these systems does one understand them at all. 

The multi-layer article is made using moulds between which a cavity clearance is freely set. A skin material lined with foam is placed between the upper and lower moulds and molten PP containing a chemical blowing agent is supplied through a resin melt conduit in the lower mould when the cavity clearance is between (C plus 15) mm and (C plus 50) mm, where C is the thickness of the skin material lined with the foam. The upper mould is lowered at a specific rate and the molten resin is pressed at a specific pressure to fill the cavity ends with the molten resin to complete the moulding of the resin body. The body is pressed for a certain time to form a skin layer, the upper mould is lifted up to decrease the compression pressure of the skin material lined with the foam to a pressure lower than the blowing pressure of the PP resin to form and solidify the foamed body, the upper mould is lowered to apply pressure to the moulded article and finally the article is cooled in the mould. 

A glass or two of this water is added whenever you see that it threatens to rise and form a foam. The saltpeter solution is boiled until it becomes clear and of bluish color indicating that most of the water has been evaporated. It is then drawn off and placed in casks and allowed to solidify. It is then placed in wooden casks and allowed to stay three or four days, and then decanted, either by inclining the vessel or by holes in the bottom. The decanted water is saved and reboiled. The solidified saltpeter is then chiseled out and washed with its own solution then placed on tables to dry thoroughly. ... 

---