Permeability physical characteristics

The introduction of large gas phase volumes into the polymer alters the physical characteristics of the material volume weight, permeability to fluids and gases, and physico-mechanical properties. Moreover, the properties of the polymer matrix itself are changed (owing to orientation effects, supermolecular structure of the polymer in the walls, ribs and tension bars of cells), which drives up the value of specific strength on impact, and results in anisotropy of elasticity. 

Vulcanised butyl rubber is very similar to vulcanised natural rubber in various physical characteristics but has better resistance to oxidation and has low permeability to gases. Hence, it is widely used in tubes for cycles, scooters, motor cars, etc. It is also used as rubber in many other applications. 

Owing to their stmctural similarity to the macromolecular-based components in the body (and their biocompatibility, permeability, and physical characteristics), hydrogels can also serve as a synthetic extracellular matrix (ECM) to organize cultured cells into a three-dimensional architecture and to present stimuli that direct the growth and formation of a desired tissue [33]. The balance between mechanical properties and controlled degradation of hydrogels mainly depends on the original... 

Notwithstanding these factors, the physical characteristics of compounds for optimal intranasal absorption are the same as for other absorption routes. The drug must dissolve in the fluids of the nasal mucosa and must be sufficiently lipophilic to cross the membranes of the nasal epithelium. Nasal absorption is facilitated by the high permeability of small venules and capillaries associated with the nasal mucusa. 

Air permeability is a standard physical characteristic of the medium s porosity and is defined as the volume of air that can pass through one square... 

This correlation is useful for rapid estimation of the blood-brain barrier permeability. More accurate estimation can be obtained by examining other physical characteristics of the compound, such as cross-sectional area and critical micelle concentration [27] (Figure 5.28). Because of the extremely low permeability of brain capillaries to most molecules, brain endothelial cells have a variety of specialized transport systems—including transporters for glucose, amino acids, insulin, and transferrin—that enable essential molecules to move from the blood into the brain extracellular space. Useful reviews of the blood-brain barrier are available [28, 29]. 

The coating material is an inert substance, which coats on core with desired thickness. Generally, hydrophilic polymers, hydrophobic polymers, (or) a combination of both are used for the microencapsulation process. The film thickness can be varied considerably, depending on the system. Surface area of the material to be coated and other physical characteristics of the coating materials used in microencapsulation methods are amenable, to some extent, to in situ modification. The list of a specific coating material is a lengthy. Table 47.1 provides the list of various polymers employed in microencapsulation. The typical coating properties such as cohesiveness, permeability, moisture... 

The physical properties of bilayers are different from cell membranes in that they have extremely high resistance (10 J2/cm ) and usually a low capacitance (typically 0.5 tF/cm ). However, when the ionic permeability of bilayers is increased with various agents the resistance falls and the capacitance may increase producing models whose physical characteristics are, superficially at least, similar to biological membranes. 

Other interesting and potentially useful physical characteristics of conventional vesicles include their activity as osmotic membranes, their ability to undergo phase transitions from liquid crystalline to a more fluid state, and their permeability to many small molecules and ions, especially protons and hydroxide. Because of their similarity to natural biological membranes, vesicles also have great potential as models for naturally occurring analogues that may be difficult to manipulate directly. 

The water vapor permeability of a material is defined by its ability to let water vapor pass through it under the action of pressure between its two opposite faces. This quantity depends on the physical characteristics of such material, ie, pore diameter and tortuosity, and has a close relationship with air permeability. Water vapor permeability of the fabric increases with increasing air permeability [28,33]. 

Fillers influence the whole spectrum of physical characteristics of a rubber, including hardness, strength, extensibility, heat build-up, vibration damping, electrical insulation or conductivity, colour, long-term ageing performance, permeability to fluids, swelling in and absorption of fluids, and adhesion to substrates. 

Both the chemical composition and structural configurations of the polymeric support play an important role in cation permeability (48). Pu(IV) was deliberately chosen for our study since its alpha radiolysis might cause appreciable structural damage to the polymeric support. Descriptions of some of the hydrophobic supports that we have evaluated and their physical characteristics of porosity, pore size, thickness, and critical surface tension are listed in Table 6. 

Starches (CeHioOs)] Odorless, no taste. Modify physical properties of food products, contributing mainly to texture, viscosity, gel formation, adhesion, binding, moisture retention, product homogeneity and film formation Odorless, tasteless, and colorless. Low permeability to oxygen. Low cost of production. Physical characteristics, chemical resistance and mechanical properties similar to those of plastic films. 

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