Membrane cross-section

Fig. 2. A series of progressively closer (scanning electron microscope) SEM photographs of the same membrane cross section, clearly showing skin and...

Fig. 5. Scanning electron micrographs of hoUow fiber dialysis membranes. Membranes in left panels are prepared from regenerated cellulose (Cuprophan) and those on the right from a copolymer of polyacrylonitrile. The ceUulosic materials are hydrogels and the synthetic thermoplastic forms a microreticulated open cell foam with a tight skin on the inner wall. Pictures at top are membrane cross sections those below are of the wall region. Dimensions as indicated.

The membrane area was chosen to give the optimum combination of economies of scale, ease of handling, and use of available raw material and membrane sizes. This led us to a membrane cross sectional area of approximately 3 m2. 

Figure 3b. SEM photomicrograph of composite membranes cross-section of a NS-100 composite membrane showing the porous polysulfone substructure.

Sosinsky GE, Jesior JC, Caspar DLD, Goodenough DA Gap junction structures. VIII. Membrane cross-sections. Biophys J 1988 53 709-722. 

Figure 1. Cross-section of a membrane functionalized with MPE functional groups imaged by x-ray dot mapping of phosphorous. The sparse black dots represent the background level of the epoxy used to mount the sample, while the concentrated band represents the membrane cross-section.

Fig. 4. Schematic phospholipid membrane cross-section composed of double aggregates of hydrocarbons and oxygen polyhedra. Glycerol is presented schematically the PC -residues have been omitted. The molecular dimensions are based on the Na+0 octahedron (after Matheja and Degens48))...

Cross-section structure. An anisotropic membrane (also called asymmetric ) has a thin porous or nonporous selective barrier, supported mechanically by a much thicker porous substructure. This type of morphology reduces the effective thickness of the selective barrier, and the permeate flux can be enhanced without changes in selectivity. Isotropic ( symmetric ) membrane cross-sections can be found for self-supported nonporous membranes (mainly ion-exchange) and macroporous microfiltration (MF) membranes (also often used in membrane contactors [1]). The only example for an established isotropic porous membrane for molecular separations is the case of track-etched polymer films with pore diameters down to about 10 run. All the above-mentioned membranes can in principle be made from one material. In contrast to such an integrally anisotropic membrane (homogeneous with respect to composition), a thin-film composite (TFC) membrane consists of different materials for the thin selective barrier layer and the support structure. In composite membranes in general, a combination of two (or more) materials with different characteristics is used with the aim to achieve synergetic properties. Other examples besides thin-film are pore-filled or pore surface-coated composite membranes or mixed-matrix membranes [3]. 

Figure 6.2. Schematic illustration of a cell membrane (cross-section)...

FIGURE 25.6 (a) Schematic representation of the YBCO membrane (i) top layer of sol-gel derived YBCO (ii) YBCO-MgO composite intermediate layer (iii) YBCO macroporons snpport. (b) SEM image of the YBCO membrane (cross-section). 

FIGURE 25.19 SEM observation of a sodalite/aAl203 membrane obtained by secondary growth of a seeded membrane (cross-section). (From Julbe, A., Motuzas, J., Cazevielle, R, Voile, G., and Guizard, C., Separ. Purif. TechnoL, 32, 139, 2003.)... 

The simplest catalyst-membrane system is shown in Fig. 1. The membrane cross section is shaded, and the catalyst is marked by black spots. The reaction A + B > C... 

Stationary fuel cell operation requires a steady flow of protons through all membrane cross sections, perpendicular to the transport direction. Proton flow induces water transport from anode to cathode by electroosmotic drag [78], Taken alone, this effect would lead immediately to membrane dehydration and to a drastic increase of its ohmic resistance. However, accumulation of water on one side of the membrane inevitably causes a backflow of water. The balance between this backflow and the electroosmotic flow leads to a stationary profile of water across the membrane. 

The thermodynamic description of the formation of mlcroporous systems by means of the phase diagrams, eis illustrated in Figures 1 to 3, is based on the assumption of thermodynamic equilibrium. It predicts under what conditions of temperature and composition a system will separate into two phases and the ratio of the two phases in the heterogeneous mixture. As related to the membrane formation procedure, the thermodynamic description predicts the overall porosity that will be obtained at specified states. However, no information is provided about the pore sizes, which are determined by the spatial distribution of the two phases. Equilibrium thermodynamics is not able to offer any explanation about structural variations within the membrane cross-section that is, whether the membrane has a symmetric or asymmetric structure or a dense skin at the surface. These... 

Figure f. Scanning electron micrographs of membrane cross-sections with typical structures ... 

Figure 10. Scanning electron micrographs of membrane cross-sections prepared from a solution of 15 % polyamide in a) DMAc b) 75 % DMAc and 25 % benzene and c) 60 % DMAc and 40 % benzene by precipitation in water at room temperature.

Figure 1. SEM image and X-ray maps of failed 60wt%Pd membrane cross-section. Sulfur has accumulated preferentially in the Au braze at the membrane-braze interface and appears to have migrated a substantial distance into the Ni-Cu support ring. (Sup = support ring, Mem = membrane foil, Brz = braze area)...

When the Pd membrane was exposed to 1000 ppm H2S, an immediate flux decrease of about 25% was observed. Figure 7(a). Then over the rest of the 120 hours of exposure, the flux continued to decrease until at 120 hours it had dropped by about 70%. Preliminary examination of the exposed membrane indicated that a highly modified, very porous surface had developed as shown in Figure 8(a). EDS of the membrane cross-section indicated about an 18 pm thick layer of sulfide had grown on the membrane surface during testing. Figure 8(b). 

Figure 7. Membrane cross-section for cyclohexanone content of 32 wt % of additive solution...

Figure 9.1 Schematic representation of membrane cross-sections [2]. Reproduced with kind permission of Kluwer Academic Publishers.

Figure 35-3. Schematic representation of membrane cross sections.

The neutral, microporous films represent a very simple form of a membrane which closely resembles the conventional fiber filter as far as the mode of separation and the mass transport are concerned. These membranes consist of a solid matrix with defined holes or pores which have diameters ranging from less than 2 nm to more than 20 //m. Separation of the various chemical components is achieved strictly by a sieving mechanism with the pore diameters and the particle sizes being the determining parameters. Microporous membranes can be made from various materials, such as ceramics, graphite, metal or metal oxides, and various polymers. Their structure may be symmetric, i.e., the pore diameters do not vary over the membrane cross section, or they can be asymmetrically structured, i.e., the pore diameters increase from one side of the membrane to the other by a factor of 10 to 1,000. The properties and areas of application of various microporous filters are summarized in Table 1.1. 

Figure 1.14 Scanning electron micrograph of membrane cross sections with typical structures (a) symmetric microporous membrane without a "skin" (b) asymmetric membrane with a "finger"-type structure and a dense skin at the surface (c) asymmetric membrane with a "sponge"-type structure, a dense skin, and pore sizes increasing from the surface to the bottom side (d) symmetric membrane with a sponge structure, a dense skin and a uniform pore size distribution in the substructure.

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