Permeability oxide membranes permeation

Direct fluorination of polymer or polymer membrane surfaces creates a thin layer of partially fluorinated material on the polymer surface. This procedure dramatically changes the permeation rate of gas molecules through polymers. Several publications in collaboration with Professor D. R. Paul62-66 have investigated the gas permeabilities of surface fluorination of low-density polyethylene, polysulfone, poly(4-methyl-1 -pentene), and poly(phenylene oxide) membranes. 

A simple method to measure the membrane permeability to specific molecules has been presented by G. Battaglia and coworkers [141], The authors encapsulated highly hydrophilic 3,3, 3//-phosphinidynetris-benzenesulfonic acid (PH) into polyethylene oxidc)-co-poly(butylene oxide) (EB) vesicles and monitored its reaction with 5,5/-dithiobis-2-nitrobenzoic acid (DTNB) penetrating the membrane from the exterior. The reaction rate (amount of the formed product as a function of time after DTNB addition) measured with IJV/Vis was directly correlated to the permeability of the permeating molecule. A comparison of these results with the permeability of egg yolk phosphatidylcholine (PC) vesicles showed that EB membranes have a more selective permeability toward polar molecules than the phospholipids membranes. Also in this case the permeability appeared to depend on the membrane thickness as predicted by Fick s first law. 

Yamamoto A, Okagawa T, Kotani A, Uchiyama T, Shimura T, Tabata S, Kondo S, Muranishi S (1997) Effects of different absorption enhancers on the permeation of ebira-tide, an ACTH analogue, across intestinal membranes. J Pharm Pharmacol 49 1057-1061 Yamamoto A, Tatsumi H, Maruyama M, Uchiyama T, Okada N, Fujita T (2001) Modulation of intestinal permeability by nitric oxide donors implications in intestinal delivery of poorly absorbable drugs. J Pharmacol Exp Ther 296 84-90... 

The feasibility of the palladium membrane system with an oxidation reaction on the permeation side and 1-butene dehydrogenation reaction on the reaction side in a membrane reactor has been successfully demonstrated. The palladium and its alloy membrane not only can withstand high temperature but also are selectively permeable to hydrogen... 

Even more important is the fact that most PEM materials (see below) are also quite permeable for water and methanol. Thus, thin membranes lead to substantial transport of these molecules from the anode side to the cathode (e. g., [25-29]). The permeation of methanol in the DMFC is undesirable for the obvious reason that it reduces the cell power ( mixed potential formation ), because no electrical work is generated in a cathodic oxidation reaction. Furthermore methanol on the cathode is unfavorable because it can block adsorption sites needed for the oxygen reduction reaction. The presence of methanol may even alter the rate constant of the oxygen reduction reaction. A typical solution to the problem of methanol transport is the use of dilute aqueous solutions of methanol, which assures almost complete oxidation when the anodic catalyst loading is high enough [30],... 

The permeabilities of oxygen through the Vycor were constant with the pressure difference and decreased with the square root of the temperature (figure not included). So the main mechanism for gas permeation is Knudsen diffusion. However, the permeabilities of oxygen through the V20s-coated catalytic membrane were deviated from Knudsen diffusion. As the partial oxidation proceeded, the... 

A novel principle for increasing the selectivity is the use of an ion gate membrane. Here, the ion permeability is controlled by electrochemical regulation of the redox state of the membrane material. For example, a polypyrrole film has to be in the reduced state to become permeable for anions. If the film is oxidized, no anion can permeate (Burgmayer and Murray, 1982). 

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