Wet membranes

Proton mobility (D J and water self-diffusion coefficient (D q) as a function of the water volume fraction (X ) in Nafion and SPEEKK, where X, = volume of water in membrane divided by volume of wet membrane. (From Kreuer, K. D. 2001. Journal of Membrane Science 185 29-39.)... 

Later, Hinatsu et al. studied the uptake of water, from the liquid and vapor states at various temperatures, in acid form Nafion 117 and 125, and Aciplex and Flemion membranes, although the latter two similar products will not be discussed here. These studies were motivated by a concern over the deleterious effects, involving either overly dry or overly wet membranes, on electrical conductivity within the context of polymer electrolyte fuel cells and polymer electrolyte water electrolyzers. 

After electrotransfer the wet membrane is rocked in about 1 ml of Soln. A per square centimeter of membrane at RT three times for 10 min each. ... 

Wipe off remaining antibody dilution after incubation with filter paper and incubate the wet membrane in Soln. B for 30 min. Rinse with Soln. C and stop the fixation by incubation with Soln. D for 2 min. Block with Soln. E for 30 min, wash three times with Soln. C, and dry in vacuo. 

Place a glass plate somewhat larger than the gel over a tray filled with Soln. D. Wet thick filter paper, e.g., Whatman 3MM, with Soln. D and spread it over the glass plate, the ends dipping into Soln. D. Now place the gel on the filter paper and remove air bubbles. Cover the sides of the gel by strips of plastic wrap and put the wetted membrane onto the gel. 

Place three soaked sheets of filter paper on the anode, one on top of the other The sheets should be saturated, but not dripping with excess buffer. Place the sheet of wet membrane on top of the filter paper stack and cover with the gel. Roll a glass rod (or similar) over the surface of the gel to push out any air bubbles, and to ensure good contact between the gel and the membrane. Finally, place the three remaining sheets of soaked filter paper on top of the gel... 

With large-surface-area membrane filter media, the interpretation of the true bubble point can be further complicated because of the diffusion of the test gas through the media. Because the filter media are more than 70% void space, a liquid-wetted membrane is virtually a thin film of liquid across which a test gas will diffuse, governed by Fick s law. 

Contrary to the diffusion test, where the air diffused through the wet membrane causes a pressure drop at the inlet side, in the WIT, the pressure drop is caused through the lowering of the water level at the upstream side of the housing. 

A. Place a wet membrane sheet on a white absorbent paper sheet. 

Membrane material/wetting Membrane Pore geometry/porosity Pore diameter Membrane... 

Place two wetted pieces of Whatman (Clifton, NJ) 3MM paper and the wetted membrane into the manifold. Load each well with 10 X SSC and adjust the vacuum so that the wells take at least 30 sec to empty. If the vacuum is strong enough to draw the solution through in 1 — 10 sec, the result can be asymmetrical signals on the autoradiograph, which cannot be scanned accurately. 

Membrane modules should always be stored in a cool, dark place out of direct sunlight and kept from freezing. Wet-tested membranes should be stored at no lower than about 5°C to prevent freezing of the sodium metabisulfite preservative solution (FilmTec membranes can go to -4°C).6 Dry membranes will not be affected by freezing temperatures. (Note that once wetted, membranes should not be allowed to dry out, as irreversible loss of flux may occur.)... 

Brackish water membranes can be shipped from the manufacturer wet or dry. Wet membranes have been performance tested at the factory. However, testing is usually conducted for shorter (hours) versus longer (days) periods. As noted in Figure 14.2 (Chapter 14.3.2), there is a period of time after start up during which membrane performance is not stable due to compaction. Flux and rejection both decrease during this period. Unless a membrane is wet tested until stable performance is achieved, the performance specifications for that membranes based on the wet test are not accurate.7... 

Ammonia is absorbed rapidly by the wet membranes of body surfaces as ammonium hydroxide, converted to urea, and excreted by the kidneys [1389], The capacity of detoxification via urea is sufficient to eliminate the ammonium ion when ammonia is inhaled in nonirritating concentrations. The inhaled ammonia is partly neutralized by carbon dioxide present in the alveoli [1390], Only a small fraction of the ammonia is exhaled unchanged by the lungs (12.3 % at an inhalation concentration of 230 ppm) [1391]. Repeated inhalation can cause a higher tolerance because the mucous membranes become increasingly resistant [1392], Additional information on the toxicology of ammonia can be found in [1393]-[1409]. 

A numerical integration technique is applied to calculate the aluminum ion concentration at intermediate times. The input parameters are (1) initial concentration of the ions in the feed and the sweep solutions, CAi,feed> Cai,sweep Cn.feed CH,sweep (2) volume of the two solutions, Vfeed and Vsweep (3) area of exchange A, (4) self-diffusion coefficient Dai and Dai/Dh determined from Step 4, and (5) wet membrane thickness, L. Two sets of equations are generated from the isotherm plot for... 

The decrease in pressure can come from two sources 1) the diffusive loss across the wetted filter. Because the upstream side pressure in the holder is constant, it decreases progressively as all the while diffusion takes place through the wetted membrane and 2) the source of pressure decay could be a leak of the filter system set-up. 

Cut squares from wet membrane with a scalpel and ruler and place squares, face upward, into wells of a 96-well tray. 

Apply gel and cover carefully with wetted membrane. 

Expose wetted membrane to X-ray film (e.g., Kodak XAR) immediately (or incubate at 37°C for 30 min to obtain steady-state light emission). Light emission remains constant for about 24 h. Multiple exposures from a single blot may thus be made to obtain an optimal signal/noise ratio. Background in substrate should be less than 25 TLU (Turner light units) over 1 h from 100 jxl of substrate, whereas 10 mol of APase should yield >10 TLU. 

Cut a nitrocellulose membrane to a size slightly smaller (a few mm) than the gel and float on deionized water (Table 8.5). If the membrane does not wet evenly from underneath within a few minutes, another membrane should be taken (unsatisfactory membranes can be autoclaved between 3MM filter papers soaked in 5 x SSC and stored wet in sealed bag). The wetted membrane is then immersed in the transfer buffer (e.g., 10 min 20 X SSC or 1 M NH4OAC). 

Summary. We have shown that ion transport in "Nafion" per-fluorinated membrane is controlled by percolation, which means that the connectivity of ion clusters is critical. This basically reflects the heterogeneous nature of a wet membrane. Although transport across a membrane is usually perceived as a one-dimensional process, our analysis suggests that it is distinctly three-dimensional in "Nafion". (Compare the experimental values of c and n with those listed in Table 7.) This is not totally unexpected since ion clusters are typically 5.0 nm, whereas a membrane is normally several mils thick. We have also uncovered an ionic insulator-to-conductor transition at 10 volume % of electrolyte uptake. Similar transitions are expected in other ion-containing polymers, and the Cluster-Network model may find useful application to ion transport in other ion containing polymers. Finally, our transport and current efficiency data are consistent with the Cluster-Network model, but not the conventional Donnan equilibrium. 

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