Electrolytic permeation

Another point of importance about the film structure is the degree to which it can be permeated by various ions and molecules. It is of course essential that supporting electrolyte ions be able to penetrate the film, else the electrical double layer at the electrode/polymer interface could not be charged to potentials that drive electron transfers between the polymer and the electrode. The electroneutrality requirements of porphyrin sites as their electrical charges are changed by oxidation or reduction also could not be satisfied without electrolyte permeation. With the possible exception of the phenolic structure in Fig. 1, this level of permeability seems to be met by the ECP porphyrins. 

Diamond JM and Wright EM (1969) Molecular Forces Governing Non-Electrolyte Permeation Through Cell Membranes. I1 roc. R. Soc. London Ser. B-Biol. Sci. 172 pp 273-316. 

Diamond, J.M. and Wright, E.M. (1969) Molecular forces governing non-electrolyte permeation through cell membranes. Proc. Roy. Soc. B., 172 273-316. 

Sawada, T. Ogawa, T. Tomita, M. Hayashi, M. Awazu, S. Role of paracellular pathway in non-electrolyte permeations across rat colon epithelium enhanced by sodium caprate and sodium caprylate. Pharm. Res. 1991, 8, 1365-1371. 

One important conclusion here is that electrolytic permeation is usually governed by the transport of the slowest component(s). More complicated cases of the ambipolar diffusion are considered in the following sections. 

Figure 4.6 Surface pH hypothesis for weak acids and bases. A model for the influence of the microclimate pH in rat proximal jejunum on weak electrolyte permeation. The weak acid A is converted to neutral by the presence of H+ in the microclimate. The undissociated form can easily be absorbed through the mucosa. In contrast, the weak base B is protonated by the H+ to BH+ which is less absorbed through the membrane.

Non-electrolytes permeate membranes by dissolution and diffusion permeation depends on both molecular size and solubility within the membrane phase. 

Any moisture contamination of the cell has a deleterious effect on its operation. Therefore, all cell assembly operations are usually carried out in a dry room or dry box. Alternatively, the cell then may be put in a heated vacuum oven for 16-24 h in order to extract residual water from the cell core before electrolyte filling. In the next process, the cell is filled with the electrolyte using a vacuum injection apparatus. Electrolyte is added to the cell by a precision pump and then vacuum filled to ensure that the electrolyte permeates and completely fills the porosity in the separator and electrode structures. Precision pumps meter the exact amount of electrolyte needed for good cell operation. The electrolyte salt usually is LiPF dissolved in a... 

Increasing the length of the alkyl chain beyond 7-9 carbon atoms produces an increase in both the mean conjugation length of the polymer chain and the electrochemical reversibility as illustrated by the symmetry of the cyclic voltammograms [64,128]. The absence of hysteresis, i.e. of a high separation between forward and backward peak potentials, may be due to a better solvation, with electrolyte permeation, of the polymers. 

Based on the results in the previous section, a new design of hybrid structure is required to improve the cross-linking and density of the coatings to prevent rapid electrolyte permeation. The new design is supported by two modifications [30] ... 

Electrolyte is metered into the cell by a precision pump and vacuum filled to ensure that the electrolyte permeates and completely fills the available porosity in the separator and electrode stmctures. Precision pumps meter the exact amount of electrolyte needed for good ceU operation. The amount of electrolyte is generally arrived at by trial and error, based on the performance of the cells. The electrolyte is invariant (same number of Li" ions enter as leave the electrolyte during charge and discharge). The electrolyte salt is usually LiPFe dissolved in organic carbonate solvents (see the ch ter on Liquid Electrolytes by J. Yamaki). Each manufacturer has a different combination of solvents with ethylene carbonate (EC) being a common denominator for most... 

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