Membranes sandwich components

Electrodialysis — In electrodialysis electrically charged - membranes and an electrical potential difference are used to separate ionic species from an aqueous solution and uncharged components. It refers to an industrial-scale process of electrolyte concentration/depletion due to separation on anion- and cation-exchange membranes under the influence of an electric field. The electrodialysis cell is constructed like a bipolar filter-press electrolyzer, with anion-exchange membranes sandwiched alternately with cation-exchange membranes, see following Figure. 

AGM — membrane sandwich. The combination of a membrane with an AGM separator has been investigated with a view towards controlling the oxygen transport as well as improving the compressive properties of the separator. With reference to the latter aspect, a AGM-membrane sandwich has been evaluated [19]. The AGM consisted of 100% fine fibres, and the incompressible polymer membrane was a mixture of polyvinyl chloride and 5-10 wt.% silica, which was partly extracted to increase the pore size and porosity. The properties of the two separator components are summarized in Table 7.9 [22]. 

FIGURE 24.10 Schematic cross section of the polypyrrole/polycarhonate/polypyrrole sandwich membrane with the epoenzyme entrapped in the pores. The membrane is drawn as coming out of the plane of the paper. The various components are not drawn to scale. (From Lakshmi, B.B. and Martin, C.R., Nature, 388, 758, 1997. With permission.)... 

An important component of the cuticle structure is the cell membrane complex, or CMC, which consists of a (8) proteinaceous layer, sandwiched by two (fJ>) lipid layers. The CMC is the only continuous structure in hair. It acts as a cement between different layers or components of the hair fiber and is responsible for the physical integrity of the hair structure. 

The work done by Adam Langmuir on monolayers has had many repercussions. Not least was that it was from these two great men that I drew the concepts which enabled me to develop the basic principles of cell membrane structure in the 1930 s. These defined cell membranes has having a lipid bilayer as their continuous phase, sandwiched between two protein layers, and penetrated by hydrophobic proteins. There are now some thousands of biologists studying these membranes, and the source of concepts remains in the work of Adam and Langmuir. I wish we knew as much about the protein components as we do about the lipids. 

In the sandwich assay format, two biorecognition elements directed to either the same epitope present multiple times on the analyte surface or the different epitopes on the target analyte are utilized. For immunoassays, this format is useful for large analytes with multiple antigenic sites. Here, one antibody is immobilized onto a porous membrane and serves as the capture antibody, while the other is conjugated to a detectable species. The response is directly proportional to the concentration of analyte in the sample. A band consisting of a secondary antibody may also be present to serve as a control that the assay components worked and the assay was run correctly. This assay format is depicted in Fig. 4. 

Non-porous membranes can be used for extraction of polar and non-polar compounds from liquid samples using only minimal amount of organic solvent. A non-porous membrane is a liquid or a solid (e.g. polymeric) phase sandwiched between two other phases, usually aqueous but can also be gaseous (8). One of these two phases contains the components to be extracted, i.e. the donor phase. On the other side of the membrane is the acceptor phase, i.e. where the extracted components are collected. Usually, the membrane unit is made of two blocks of inert material with a machined groove in each. The membrane is placed in-between these blocks and clamped together, so that a channel (typically 10-1000... 

An example of a sensor utilizing these three components is illustrated in figure 1.2, which shows a schematic of a typical enzyme electrode for the detection of glucose (also see chapter 17 of this text). The bioactive surface consists of immobilized glucose oxidase (GOD) sandwiched between a polycarbonate and cellulose acetate membrane. The transducer is a platinum electrode and the electronics are those typically found in any polarograph, i.e. an electronic system to measure low currents (on the order of microamperes) at a fixed voltage bias on the platinum electrode. The action of glucose... 

A component of a fuel cell that consists of a polymer membrane electrolyte coated with (or sandwiched between) positive and negative electrodes and then placed between bipolar plates. 

The main component of a solid oxide fuel cell is a three-layered sandwich consisting of anode, electrolyte, and cathode, each being made from a different oxide ceramic material. Such ceramic structures can be fabricated by various methods including slip or tape casting, injection molding, ceramic coverings, etc. [1]. Whatever the method applied is, it should provide the best able microstructure and specified performance of materials besides the desired shape of a SOFC membrane. However, layers of the membrane have different properties that requires combination of two or more different methods of ceramic engineering in the component fabrication. 

Audunsson [29] reported on a sandwich-type extraction module equipped with liquid membranes, prepared by immersing hydrophobic microporous membranes (e.g. PTFE membranes) in organic solvents for about 15 min. The inert men ranes then act as supports for the immobilized solvent. When an aqueous sample passes by the membrane, non-ionic components in the sample are extracted into the hydrophobic liquid film and transferred into an appropriate acceptor solution on the other side of the membrane. When the acceptor remains stagnant while the sample flows continuous ) for a defined period, a preconcentration is effected in the acceptor solution, which is subsequently transferred to the detector. The procedure is equivalent to extraction and back-extraction in a single step. More details on such a system used for sample cleanup in gas-liquid chromatography is presented in Sec. 3.7. 

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