Homogeneous solid-state membrane

More recent investigations of C. Harzdorf [84] have shown that thick layers electrolytically deposited on silver (for example anodized for one hour at 1 mA/cm in 1 M KQ, KBr, 0.1 M K1 solution and finally clearly polished with a soft rag) are completely equivalent to the homogeneous solid-state membrane electrodes. 

Due to its large compressibility, silver sulfide serves, for many manufacturers, as a basis material for halide as well as metal electrodes. In this case only about 30% of the corresponding silver halide is used relative to silver sulfide, and the mixture is compressed at higher pressures and temperatures. It is, strictly speaking, no longer a homogeneous solid-state membrane. 

The operational characteristics of homogeneous solid-state membrane electrodes are generally quite similar. As long as the inner shunt system is not an easily polarizable solid-solid contact [4], these electrodes can handle relatively high measuring circuit currents without deviating from Nernstian response (after correcting for the i R potential drop). 

As a rule, the homogeneous solid-state membrane electrodes do not need to be conditioned. They can be stored dry and are immediately ready for use. Cleaning (sanding and polishing) is only necessary if the electrode has been poisoned by contacting a solution containing an ion which forms a less soluble precipitate with the measured ion than does the corresponding electrode counter ion. 

Table 2. Homogeneous solid-state membrane electrodes... 

Since they operate in the same fashion, the electric and electrochemical properties of the heterogeneous solid-state membrane electrodes on the market today resemble those of the homogeneous precipitate membrane electrodes in many ways. The most important data are summarized in Table 3. By the same principles outlined in the previous chapter, the heterogeneous iodide electrode can also detect cyanide. In contrast to the homogeneous membranes, those which include silicone rubber as a support ma-... 

Decatungstate, in the form of a lipophilic tetrabutilamonium salt ((n-C4H9N)4 W10O32), has been homogeneously dispersed in porous membranes made of PVDF (PVDF-W10). Solid-state characterization techniques confirmed that catalyst structure and spectroscopic properties of decatungstate have been preserved once immobilized within the membranes [42-44]. 

Casting the complex solution of a metalloporphyrin and a polymer ligand such as poly(vinylimidazole-co-alkylmethacrylate) (Olm in Fig. 9-8), for example, on a Teflon plate and drying, yielded both a homogenously dispersed metalloporphyrin in a solid state and a mechanically tough membrane [26]. The Tg of the membrane was increased, for example, from -1 °C for the Olm itself to 6 °C and the membrane became brittle after the incorporation of 40 wt.% cobalt porphyrin this was explained by the stiffening effect of the incorporated... 

Figure 2 Basic types of ISE (A) glass electrode (B) electrode with a solid homogeneous or heterogeneous membrane (C) classical liquid membrane electrode (D) electrode without internal solution (all-solid-state electrode) (E) coated-wire electrode. 1, Internal standard solution 2, internal reference electrode (Ag/AgCI) 3, membrane 4, glass or plastic body of the electrode 5, reservoir of the electroactive substance solution 6, solid-state contact and 7, metal wire.

The issue of what causes line broadening in solid-state NMR was thoroughly investigated by Su et al To understand the linewidth contributions to membrane protein NMR spectra, T2 relaxation times of uniformly labeled residues which show that the homogeneous line widths are determined by conformation-independent factors, including residual dipolar coupling, J-coupling, and intrinsic T2 relaxation. Examples of this were shown by TAT and other peptides. 

In this section, PVA was blended with polyepichlorohydrin (PECH) in DMSO solution to prepare the PVA/PECH blend polymer membrane. The blend membrane was immersed in 6 M KOH aqueous solution to form the alkaline PVA/PECH SPE. It was improved in chemical, mechanical, and electrochemical properties [37]. The optimal blend ratio of PVA PECH was foimd to be 1 0.2. This polymer blend formed a imiform and homogeneous film. High PECH content, such as PVA PECH (1 1), resulted in phase separation morphology. The solid-state Zn/air batteries with PVA/PECH blend polymer electrolytes have been assembled and the test results are listed in Table 2. 

Phase inversion is known to be an effective way to create porous structures in membranes, where a competitive mutual diffusion between solvent and nonsolvent occurs to yield the porous structure. Phase inversion can be described as a demixing process whereby the initially homogeneous polymer solution is transformed in a controlled manner from a liquid to a solid state [24]. Apart from immersion in a nonsolvent bath, or immersion precipitation (IP), a variety of related techniques, such as precipitation by solvent evaporation, precipitation by absorption of water Irom the vapor phase, and precipitation by air cooling, corresponding to thermally induced phase separation (TIPS), vapor-induced phase separation (VIPS), and air-casting phase separation... 

Inside living cells, enzymes exist in an extremely structured environment, which may have the form of a gel, a membrane or other solid state assemblies. Under these conditions, the behavior of immobilized enzymes towards their inhibitors is very different from that in the homogeneous phase. The mode of enzymatic inhibition is variable from one inhibitor to another, and may also be reversible or irreversible. Inhibition may be observed with enzyme sensors without having to resort to techniques that require long extractions, such as dialysis or gel filtration, which are normally used to separate an inhibitor from a soluble enzyme. The response of the enzyme sensor provides a continuous measure of the activity of the immobilized enzyme, whether or not its inhibitor is present. Enzyme sensors thus allow convenient and rapid study of the inhibition of enzymes and their subsequent reactivation. 

By far the most used technique for membrane preparation is the immersion precipitation method (nonsolvent-induced phase separation). A homogenous polymer solution is cast as thin him and subsequently immersed into a nonsolvent bath, typically water or mixtures of water and solvent. The dif-fusional exchange of solvent and nonsolvent brings the him solution into an instable state resulting in phase separation, either by liquid-liquid (l-l) and/or solid-liquid (s-l) demixing, depending on the type of polymer and the precipitation conditions employed [92,93]. 

The deoxy-oxy cycle was repeated at 1-min intervals and recorded 1.2 X 10 times (about 6 months) by changing the atmosphere of the cobalt-porphyrin polymer membrane from reduced pressure (about 2 cm Hg) to laboratory air pressure (76 cm Hg) at ambient temperature. Lifetime or half-life periods for the oxygen-binding ability were estimated to be 6 months for Structure (6) in the solid membrane state. The corresponding cobalt-porphyrin (6) in homogeneous toluene solution was able to repeat the oxy-deoxy cycle with a lifetime close to only 1 day. 

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