Permeable shells

The total weight of rock vaporised and melted instantaneously as the shock passes is thus approximately 310 tons per kiloton, and the initial cavity thus formed attains a radius of more than 3 metres. The weight estimated above is significantly lower than the total quantity of rock melted by the explosion, because it is necessary to take into account other melting processes, known as secondary processes. Beyond the solid matrix melting radius, over a distance of a few metres, the interstitial water is vaporised. As it expands, the high-pressure steam shatters the matrix, which is divided into particulate fines. When the cavity later expands under the effect of the thrust of the gases, part of this zone of powdered rock is recompacted and partially sintered. It forms a low-permeability shell around the cavity. 

Rapid and facile generation of capsules from tandem assembly in aqueous media is amenable to encapsulation of water-soluble compounds. Encapsulation of ICG dye within PAH/H2PO4 aggregates was shown by Yu et al. Enzyme encapsulation and the feasibility of capsules to serve as reaction vessels was demonstrated by Rana et al. In their study, they encapsulated acid phosphatase enzyme in PLL-citrate-silica sols and suspended the spheres in a solution containing fluorescein diphosphate. Fluorescence increased in intensity within the shell walls as fluorescein was formed by enzymatic cleavage of phosphate groups. This study showed that microcapsules could serve as reaction vessels that allow enzymatic action to take place in a protective environment and allow for reactants and/or products to diffuse through permeable shell walls. 

Biological membranes are supra-molecular systems whose extent in two dimensions considerably exceeds their thickness, which is of the order of 10 nm. The membranes are not passive, semi-permeable shells. They play important roles in the cell. Mitochondrial membranes are much thinner than most cell membranes their thickness is of the order of 5 nm. 

The abundance of natural and man-made polymers provides a wider scope for the choice of shell material, which may be made permeable, semi-permeable or impermeable. Permeable shells are used for release applications, while semi-permeable capsules are usually impermeable to the core material but permeable to low molecular-weight liquids. Thus, these capsules can be used to absorb substances from the environment and to release them again when brought into another medium. The impermeable shell encloses the core material and protects it from the external environment Hence, to release the content of the core material the shell must be ruptured by outside pressure, melted, dried out dissolved in solvent or degraded under the influence of light (see Chapter 7). Release of the core material through the permeable shell is mainly controlled by the thickness of the shell wall and its pore size. The dimension of a microcapsule is an important criterion for industrial applications the following section will focus on spherical core-shell types of microcapsules (Fig. 1.8). 

Oil from powder of microcapsules was extracted with cyclohexane. The amount of extracted oil from powder of microcapsules containing different oils as a function of SDS concentration in emulsion is shown in Figure 27. In microcapsules containing sunflower and mixture linen seed/sunflower oil (0.2/0.8) the lowest amount of extracted oil was found in the HPMC/SDS interaction region, at 0.35%SDS, which indicates a compact shell which hinders oil extraction from microcapsules. On the other hand, the amount of extracted pumpkin seed oil increases on increase in SDS concentration, indicating more permeable shell of microcapsules. It was shown that oil influences microencapsulation process and thus properties of microcapsules. Therefore, nature of it should be considered as an important parameter during the microencapsulation process by the presented method. 

To prevent the surrounding air from mixing with the supply air, the air shower should use air-permeable filter material with a harder, load-bearing, nonflammable outer shell and an inner layer of softer material with a high air resistance. This design requires that the supplied air be filtered. 

The prespective to be gained thus far is that in order to pass through a lipid layer an ion must have an appropriate polar shell provided in large part by the carrier or channel structure which by virtue of its conformation and by also having lipophilic side chains provides for the polar shell to lipid shell transition. While the relative permeability of monovalent vs divalent and trivalent ions can be qualitatively appreciated from the z2 term in Eqn 2, as indicated in Figure 1B, it is essential to know structural and mechanistic detail in order even qualitatively to understand anion vs cation selectivity and to understand selectivity among monovalent cations. 

Kcurentjes et al. (1996) have also reported the separation of racemic mixtures. Two liquids are made oppositely chiral by the addition of R- or S-enantiomers of a chiral selector, respectively. These liquids are miscible, but are kept separated by a non-miscible liquid contained in a porous membrane. These authors have used different types of hollow-fibre modules and optimization of shell-side flow distribution was carried out. The liquid membrane should be permeable to the enantiomers to be separated but non-permeable to the chiral selector molecules. Separation of racemic mixtures like norephedrine, ephedrine, phenyl glycine, salbutanol, etc. was attempted and both enantiomers of 99.3 to 99.8% purity were realized. 

TFF module types include plate-and-frame (or cassettes), hollow fibers, tubes, monoliths, spirals, and vortex flow. Figures 20-52 and 20-53 show several common module types and the flow paths within each. Hollow fiber or tubular modules are made by potting the cast membrane fibers or tubes into end caps and enclosing the assembly in a shell. Similar to fibers or tubes, monoliths have their retentive layer coated on the inside of tubular flow channels or lumens with a high-permeability porous structure on the shell side. 

FS Horn, SA Veresh, WR Ebert. Soft gelatin capsules II. Oxygen permeability study of capsule shells. J Pharm Sci 64 851-857, 1975. 

WA Ritchel, A Sabouni, SH Gehrke, ST Hwang. Permeability of [3H]water across a porous polymer matrix used as a rate-limiting shell in compression-coated tablets. J Controlled Release 12 97-102, 1990. 

In this section the laboratory measurements of CC -foam mobility are presented along with the description of the experimental procedure, the apparatus, and the evaluation of the mobility. The mobility results are shown in the order of the effects of surfactant concentration, CC -foam fraction, and rock permeability. The preparation of the surfactant solution is briefly mentioned in the Effect of Surfactant Concentrations section. A zwitteronic surfactant Varion CAS (ZS) from Sherex (23) and an anionic surfactant Enordet X2001 (AEGS) from Shell were used for this experimental study. 

The benefit of the LbL technique is that the properties of the assemblies, such as thickness, composition, and function, can be tuned by varying the layer number, the species deposited, and the assembly conditions. Further, this technique can be readily transferred from planar substrates (e.g., silicon and quartz slides) [53,54] to three-dimensional substrates with various morphologies and structures, such as colloids [55] and biological cells [56]. Application of the LbL technique to colloids provides a simple and effective method to prepare core-shell particles, and hollow capsules, after removal of the sacrificial core template particles. The properties of the capsules prepared by the LbL procedure, such as diameter, shell thickness and permeability, can be readily adjusted through selection of the core size, the layer number, and the nature of the species deposited [57]. Such capsules are ideal candidates for applications in the areas of drug delivery, sensing, and catalysis [48-51,57]. 

Recently, we proposed an alternative process for encapsulating biomacromolecules within PE microcapsules. This approach involves using nanoporous particles as sacrificial templates for both enzyme immobilization and PE multilayer capsule formation (Figure 7.2, route (I)) [66,67]. Unlike previous LbL encapsulation strategies, this approach is not limited to species that undergo crystallization, and is not dependent upon adjustments in electrostatic interactions within PE microcapsules to alter shell permeability characteristics. The salient feature of this method is that it is applicable to a wide range of materials for encapsulation. 

Relatively high permeability, coarse-grained, and well-sorted sandy soils with occasional shells. These soils were interpreted to be deposited in a fluvial tidal channel axis or deltaic reworked distributary mouth bar deposits. 

Porous alumina tube externally coated with a MgO/PbO dense film (in double pipe configuration), tube thickness 2.5 mm, outer diameter 4 mm, mean pore diameter 50 nm, active film-coated length 30 mm. Feed enters the reactor at shell side, oxygen at tube side. Oxidative methane coupling, PbO/MgO catalyst in thin film form (see previous column). r-750X,Pr ed 1 bar. Conversion of methane <2%. Selectivity to Cj products > 97%. Omata et al. (1989). The methane conversion is not given. Reported results are calculated from permeability data. 

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