Chloride permeability coefficient

Using regression analysis on a data set of about 50 different molecules, it was found that a. = —4.4,8 = —0.5, Df = 12 cm2/s, and =2.5x 10 5 cm2/s [192], A graphic representation of the effect of relative molecular mass (Mr) and distribution coefficient on corneal permeability is shown in Fig. 13. One observes a rapid reduction in permeability coefficient with decreasing P and increasing Mr. The addition of pores to the model, a mathematical construct, is necessary to account for permeability of polar molecules, such as mannitol and cromolyn. These would also be required for correlating effects of compounds, such as benzalkonium chloride, which may compromise the... 

Figure 5.5 Water permeability as a function of sodium chloride permeability for membranes made from cellulose acetate of various degrees of acetylation. The expected rejection coefficients for these membranes, calculated for dilute salt solutions using Equation (5.6),...

We can now consider some typical nutrient solutes like amino acids and phosphate. Such molecules are ionized, which means that they would not readily cross the permeability barrier of a lipid bilayer. Permeability coefficients of liposome membranes to phosphate and amino acids have been determined [46] and were found to be in the range of 10 11 -10 12 cm/s, similar to ionic solutes such as sodium and chloride ions. From these figures one can estimate that if a primitive microorganism depended on passive transport of phosphate across a lipid bilayer composed of a typical phospholipid, it would require several years to accumulate phosphate sufficient to double its DNA content or pass through one cell cycle. In contrast, a modern bacterial cell can reproduce in as short a time as 20 min. 

Fig. 19. Comparison of molecular weight-normalized values of the permeability coefficients of biological membranes with similar values determined for the polyelec-trolyte complex membrane of poly(sodium styrenesulfonate) (NaSS)-poly(4-vinylben-zyltrimethylammonmm chloride) (PVBMA)70 A Aminopyrine,...

As discussed previously, the different ionic concentrations on the two sides of a membrane help set up the passive ionic fluxes creating the diffusion potential. However, the actual contribution of a particular ionic species to Em also depends on the ease with which that ion crosses the membrane, namely, on its permeability coefficient. Based on the relative permeabilities and concentrations, the major contribution to the electrical potential difference across the plasma membrane of N. translucens comes from the K+ flux, with Na+ and Cl- fluxes playing secondary roles. If the Cl- terms are omitted from Equation 3.20 (i.e., if Pci is set equal to zero), the calculated membrane potential is -154 mV, compared with -140 mV when Cl- is included. This relatively small difference between the two potentials is a reflection of the relatively low permeability coefficient for chloride crossing the plasma membrane of N. translucens, so the Cl- flux has less effect on Em than does the K+ flux. The relatively high permeability and the high concentration of K+ ensure that it... 

Figure 9 (A) lontophoretic flux of various cations across excised pig skin versus molecular weight. The donor concentration was 1.0 M of drug as chloride salt. (Data from Ref. 108.) Key. ( ) monovalent ions, (O) divalent ions. (B) Normalized cathodal iontophoretic flux of anionic solutes across hairless mice versus molecular weight. (Data from Ref. 109.) (C) Cathodal iontophoretic permeability coefficient of alkanoic acid across nude rat skin versus molecular weight. (From Ref. 64.) (D) Comparison of transport number and molecular weight in human epidermis.

The splash/tidal zone of bridges and walls represent cylindrical columns immersed in water. These structures involve entry in two dimensions. Chloride ions enter concrete by adsorption at the surface, which is given by an empirical equation. The effective chloride diffusion coefficient is derived from concrete permeability, water/cement ratio, and concrete resistivity. When concentration reaches a critical value in the vicinity of steel, corrosion begins. As shown in Fig. 12.6, a boundary layer exists adjacent to the concrete... 

By adding polymer dispersions and thereby decreasing the permeability, a further reduction of the chloride migration coefficient can be achieved. The rapid chloride migration test is a quick tool to test the chloride resistance by applying a voltage [1]. In relation to the depth of cover, the risk for corrosion of the steel surface can be estimated in terms of time. 

Figure 2 shows the permeability coefficient for phenyltrimethylammonium chloride as a function of pH of the medium at different ionic strengAs. As in the case of the anion permeation shown in Fig. 1, Ae permeability coefficient of cations showed a drastic increase in Ae pH range between 4 and 6 at all ionic strengAs when Ae pH of Ae medium was raised. In Ais case, however, Ae increase in ionic strengA of Ae medium caused a decrease in Ae permeability coefficient.

Figure 2. Permeability coefficient of phenyltrimethylammonitun chloride as a function of pH at various ionic stren s 0.154(0),0.077(A),0.015(D), and 0.008(0). SD was within the size of each symbol.

Poly(vinyl chloride)(PVC)/artificial amphiphiles composite membranes were prepared in which the weight fraction of amphiphile was 15wt%. The composite membrane was obtained by evaporating solvent from a tetrahydrofuran (THF) solution of PVC and artificial amphiphile at 313 K. The diffusive permeability coefficient, P was evaluated in a normal osmosis experiment using KCl 10wt% solution and deionized water partitioned by the composite membrane. 

Permeation in the vinyUdene chloride copolymer and the polyolefins is not affected by humidity the permeability and diffusion coefficient in the ethylene—vinyl alcohol copolymer can be as much as 1000 times greater with high humidity (14—17). 

The permeability tests for alkali metal ions in the aqueous solution were also conducted. When an aqueous salt solution moves to cell 2 through the membrane from cell 1, the apparent diffusion coefficient of the salt D can be deduced from a relationship among the cell volumes Vj and V2, the solution concentration cx and c2, the thickness of membrane, and time t6 . In Table 12, permeabilities of potassium chloride and sodium chloride through the 67 membrane prepared by the casting polymerization technique from the monomer solution in THF or DMSO are compared with each other and with that the permeability through Visking dialyzer tubing. The... 

Table 4 contains some selected permeability data, including diffusion and solubility coefficients foT flavors in polymers used in food packaging. Generally, vtuylidene chloride copolymers and glassy polymers such as polyamides and EVOH are good barriers to flavor and aroma permeation, whereas the polyolefins are poor barriers. Comparison to Table 2 shows lhat the large-molecule diffusion coefficients are 1000 or more times lower tli an the small-molecule coefficients. 

Furthermore, these characterizations will be completed in determining mass transfer parameters a and Ps, Cconv and Jdiff, respectively, the reflection coefficient and the solute permeability of the membranes, the part of solute mass transfer dedicated to convection and Jam the part of mass transfer dedicated to hydration-diffusion, for two synthetic chlorides and sulphates sodium salts solutions under different concentrations, 10-3 and 10-1 M. 

Humidity does not affect the permeability, diffusion coefficient, or solubility coefficient of flavor/aroma compounds in vinylidene chloride copolymer films. Studies based on /n /w-2-hexenal and D-limonene from 0 to 100% rh showed no difference in these transport properties (97,98). The permeabihties and diffusion coefficients of /n /w-2-hexenal in two barrier polymers are compared in Table 12. Humidity does not affect the vinylidene chloride copolymer. In contrast, transport in an EVOH film is strongly plasticized by humidity. 

Comparison of the dependence of dry oxygen permeability on temperature with some conventional barrier polymers (after Watanabe)(15) are presented In Figure 9 In normalized units of cc/mV24 hours for a one mil (25.4 micrometers) film thickness. The temperature coefficient of the grafted slloxane polymer appears to be comparable to that of BAREX 210 and ethylene vinyl alcohol. The EVAL shown (EVAL-E) Is 44% by weight ethylene. The silane Is considerably better than that of the polyvinylIdene chloride (Saran 468) sample shown In the figure. The data are plotted so that the temperature Increases to the right on the abscissa. 

Other properties of concrete. For example, for concrete made with a certain type of cement, correlations between the water permeability and the diffusion coefficient of chlorides, that is between K and D, can be established. Nevertheless, when variations are made in the type of cement used, for example, changing from Portland cement to blended cement, the relationships are no longer valid (D may vary even two orders of magnitude with no corresponding variation in K [3]). 

---