Films permeation

Of particular interest in the usage of polymers is the permeability of a gas, vapour or liquid through a film. Permeation is a three-part process and involves solution of small molecules in polymer, migration or diffusion through the polymer according to the concentration gradient, and emergence of the small particle at the outer surface. Hence permeability is the product of solubility and diffusion and it is possible to write, where the solubility obeys Henry s law,... 

Thin-film permeation-barrier technology for flexible organic light-emitting devices J.S. Lewis, M.S. Weaver IEEE Journal of Selected Topics in Quantum Electronics, 10 45-57... 

Uneven distribution of the stationary phase liquid on the solid support particles causes band dispersion. This may be rationalized if one considers that molecules entering a thin part of the liquid film permeate faster than in a thick part of the liquid film. This effect causes some molecules to spend more time in the liquid phase than other molecules with their slow movement through the column and resulting widening of the band. 

Solid-gas Adsorption Solid aerosol, adsorption, catalysis, corrosion, diffusion, surface energy, thin films, permeation, osmosis, filtration, oxidation, charge transfer, condensation and nucleation... 

Balinov, B., Linse, R, and Soderman, O. Diffusion of the dispersed phase in a highly concentrated emulsion emulsion structure and film permeation, /. Colloid Interface Sci., 182, 539, 1996. 

Chloride corrosion of steel is controlled by the environment, the concentration of oxidizer, the structural characteristics of metal, the composition of the alloy, and the presence of dissolved oxygen. The chloride ions adsorb on the outer surface of the passive film, permeate through the passive oxide film, and interact with the underlying metal. 

Depending on the structure of the barrier film and the materials used, gas ingress can preferentially take place through the whole surface of the barrier film (permeation through the surface) or through the heat-sealed plastic VIP flanges (permeation at the edges), or both. 

Of high interest would seem to be improved flux and selectivity through a better polymer. Materials are reported every year with good permeability properties but many studies are carried out with relatively thick dense films on the order of 5 to 50pm. In addition, with CO2 any study with pure gas results has to be discounted until mixed gas results are reported because of CO2 plasticization. Also, thin film permeation properties have been demonstrated as different than those of thick films [37]. 

A physical model for film transport that accommodates the available experimental observations is a conventional film permeation model [10]. Candidate permeant molecules partition into a film from solution via an equilibrium process and then diffuse through the film to the electrode surface where they undergo oxidation or reduction. The redox product molecules then diffuse to the film/solution boundary and exit the film via a reverse partitioning step that, again, is sufficiently rapid to occur at equilibrium. Faradaic electrochemical techniques are especially powerful for interrogating such processes - in part because they require permeants to traverse films essentially completely in order for signals to be observed. (Recall that interfacial electron transfer can occur with reasonable efficiency only over distances of ca 10, or perhaps 20, A. Depending on the compound, these distances correspond to one or two film monolayers.)... 

While the voltammograms can be quantitatively analyzed to yield permeant transport parameters - for example, via numerical simulations - we have instead utilized rotating disk electrode (RDE) voltammetry for this purpose. Sequential solution and film transport problems are generally well described by a variant of the Koutecky-Levich analysis [11]. This analysis represents the series process Idnetically as a reciprocal sum of pure solution-phase convection/dilFusion (cd) and pure film permeation (p) rates or fluxes. Since detection is electrochemical, the fluxes can be written in terms of currents, where ilim is the observed overall, mass-transport limited, current [12] ... 

Marais, S., Bureau, E., Gouanve, E., Ben Salem, E., Hirata, Y., Andrio, A., Cabot, C., and Atmani, H. (2004) Transport of water and gases through EVA/PVC blend films-permeation and DSC investigations. 

A chitin gel can be prepared by methods other than those already described. While deacetylated chitin is chitosan, chitin can be obtained by acetylating chitosan. Chitosan is dissolved in an acetic acid solution and diluted to 50% concentration by methanol. If acetic anhydride is added to this solution at 3-1 Ox the number of moles of the amine groups present, the solution solidifies in several minutes and forms a transparent gel [23-26]. Time necessary to solidification depends on the concentration of chitosan, methanol, and acetic acid anhydride [27,28]. This gel can also be made into a thin film and the film permeates materials well [25, 26]. 

Agrell HG, Boschloo G, Hagfeldt A (2004) Conductivity studies of nanostructured TiOa films permeated with electrol)fte. J Phys Chem B 108 12388-12396... 

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