Factors affecting permeability

Barrier polymers, 3 375-405 applications, 3 405 barrier structures, 3 394-399 carbon dioxide transport, 3 403 flavor and aroma transport, 3 403-405 health and safety factors, 3 405 immiscible blends, 3 396-398 large molecule permeation, 3 388-390 layered structures, 3 394-396 miscible blends, 3 398-399 oxygen transport, 3 402 permanent gas permeation, 3 380-383 permeability prediction, 3 399-401 permeation process, 3 376-380 physical factors affecting permeability, 3 390-393... 

Comstock, G.L. and Cote, W.E., 1968. Factors affecting permeability and pit aspiration in coniferous sapwood. Wood Sci. Technol, 2 279-291. 

It is important to achieve stable permeability. Permeability is strongly affected by not only the composition but also the microstructure because it is a structure sensitive characteristic. Nomura and Ohta [ 1 ] describe the factors affecting permeability as follows ... 

Low water and oxygen permeability increase corrosion protection. Many factors affect permeability of coating films to water and oxygen (92). Coatings with a Tg above the temperature at which corrosion protection is desired reduce... 

Factors affecting permeability include the solubility and diffusivity of the penetrant into the polymer, polymer packing and side-group complexity. 

The following factors affect net diffusion of a substance (1) Its concentration gradient across the membrane. Solutes move from high to low concentration. (2) The electrical potential across the membrane. Solutes move toward the solution that has the opposite charge. The inside of the cell usually has a negative charge. (3) The permeability coefficient of the substance for the membrane. (4) The hydrostatic pressure gradient across the membrane. Increased pressure will increase the rate and force of the collision between the molecules and the membrane. (5) Temperature. Increased temperature will increase particle motion and thus increase the frequency of collisions between external particles and the membrane. In addition, a multitude of channels exist in membranes that route the entry of ions into cells. 

D. Physicochemical Factors Affecting Structure-Permeability Relationships... 

Drugs in Class II have low aqueous solubility (but high membrane permeability), and any factor affecting dissolution rate would be expected to have an impact on the absorption of such compounds. Factors that are noted in Fig. 11, such as fluid pH, volume and viscosity, and bile secretion (especially in response to fatty foods), might be expected to play a role in dissolution rate and thereby affect absorption. Compounds that fall into this class include carbamazepine, cyclosporin, digoxin, griseofulvin, and spironolactone. Food would be expected to exert a potentially significant affect on... 

Other factors affecting performance include the presence of toxic material, the redox potential, salinity of the groundwater, light intensity, hydraulic conductivity of the soil, and osmotic potential. The rate of biological treatment is higher for more permeable soils or aquifers. Bioremediation is not applicable to soils with very low permeability, because it would take a long time for the cleanup process unless many more wells were installed, thus raising the cost. 

For compacted, low-permeability soil liners, the U.S. EPA draft guidance recommends natural soil materials, such as clays and silts. However, soils amended or blended with different additives (e.g., lime, cement, bentonite clays, and borrow clays) may also meet the current selection criteria of low hydraulic conductivity, or permeability, and sufficient thickness to prevent hazardous constituent migration out of the landfill unit. Therefore, U.S. EPA does not exclude compacted soil liners that contain these amendments. Additional factors affecting the design and construction of CCLs include plasticity index (PI), Atterburg limits, grain sizes, clay mineralogy, and attenuation properties. 

The quantitative role of electrical factors affecting the transport of charged molecules is obtained by comparing permeability coefficients with the permeability coefficient P(Lcdi for molecular size-restricted diffusion independent of the charge on the molecule (i.e., the neutral image). With Eqs. (45) and (46) one obtains... 

Solubility, dissolution rate, and intestinal permeability, are the major bio-pharmaceutic factors that affect the rate and extent of absorption of an oral drug product. Particularly for water insoluble drugs that have generally high membrane permeability (BCS Class II), dissolution, and dose are the most critical factors affecting the rate and the extent of oral absorption. 

Swan, K.C. and White, N.G. (1972). Corneal permeability (1) factors affecting penetration of drugs into the cornea. Amer. J. Ophthalmol. 25 1043-1058. 

A similar phenomenon can be observed in the cuffs and balloons of tracheal tubes, flotation catheters, etc. Increases in cuff pressure may be sufficient to cause mucosal ischaemia with subsequent damage to the tracheal mucosa. In the case of pulmonary flotation catheters, there is a risk of cuff rupture followed by gas embolism and infarction. A number of factors affect the rate of volume and pressure change—time, permeability, elasticity, initial volume and pressure, nitrous oxide concentration, temperature. 

Most, if not all, milks contain sufficient amounts of lipase to cause rancidity. However, in practice, lipolysis does not occur in milk because the substrate (triglycerides) and enzymes are well partitioned and a multiplicity of factors affect enzyme activity. Unlike most enzymatic reactions, lipolysis takes place at an oil-water interface. This rather unique situation gives rise to variables not ordinarily encountered in enzyme reactions. Factors such as the amount of surface area available, the permeability of the emulsion, the type of glyceride employed, the physical state of the substrate (complete solid, complete liquid, or liquid-solid), and the degree of agitation of the reaction medium must be taken into account for the results to be meaningful. Other variables common to all enzymatic reactions—such as pH, temperature, the presence of inhibitors and activators, the concentration of the enzyme and substrate, light, and the duration of the incubation period—will affect the activity and the subsequent interpretation of the results. 

The factors affecting the selectivity and permeability of polymer membranes to different gases are best discussed on the basis of Eqs. (12) and (14). As noted in Eq. (12), the permeability coefficient, P, of a penetrant gas in a polymer membrane is the product of a (concentration-averaged) diffusion coefficient, D, and of a solubility coefficient,... 

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