Homogeneous self-supported

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]. 

When siloxane chains becomes longer than tetrasiloxane, the polymers become waxy and eventually lose their self-supporting property. The polymers show only one Tg, and the absolute Tg value is lowered significantly by the intr uction of the siloxane linkage. This clearly indicates that oligosiloxanes do not phase-separate from the main-chain component and distribute homogeneously in the membrane. (Jxygen permeability of the polymers are also depicted in Table 1. 

Polymer liquid (PL) membranes The PL membrane is a relatively new type of self-supporting liquid membrane, which resembles the SL membrane. Similarly to the SL membrane, the PL membrane incorporates a liquid extractant in the membrane polymeric structure. In some cases the incorporation of additional organic compounds (plasticizers) is required to achieve homogeneity and sufficient flexibility of the membrane. 

The most common technique in practice, to obtain a good spectrum of the fundamental vibrations of a powdered insulating material with the transmission/absorption IR technique, is to prepare a layer appropriately diluted and sufficiently thin. To do this the most used technique is that of the KBr pressed discs. KBr in fact is an easily available powdered material which does not absorb in the medium IR region (down to near 400 cm i.e. it cuts out the far IR). It can be easily mixed homogeneously with the powder to be investigated, and pressed, thus obtaiiung diluted self-supporting discs very useful for IR transmission. Other materials (such as e.g. Csl or polyethylene for far IR studies) allow the production of similar pressed discs, with cut-off limits at even lower frequencies. Alternatively, the powders can be... 

Fang et al. [46] synthesized the self-supported supercapacitor electrodes by coating PPy homogeneously on MWCNT membranes. The advantage of self-supported electrodes over the use of metal backing foils and binders is that the extra mass of these supporters is not added to composite, and it does not alter charge storage capacity of the composite. They used the pulsed potentio-amperometric... 

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