Membrane macroporous polymer

Tennikov, M. B., Gazdina, N., Tennikova, T. B., and Svec, F., Effect of porous structure of macroporous polymer supports on resolution in high-performance membrane chromatography of proteins, J. Chromatogr. A, 798, 55, 1998. 

Macroporous Polymer Membranes, Inorganic Salts, and Ice Crystals... 

Recently, the LbL technique has been extended from conventional nonporous substrates to macroporous substrates, such as 3DOM materials [58,59], macroporous membranes [60-63], and porous calcium carbonate microparticles [64,65], to prepare porous PE-based materials. LbL-assembly of polyelectrolytes can also be performed on the surface of MS particles preloaded with enzymes [66,67] or small molecule drugs [68], and, under appropriate solution conditions, within the pores of MS particles to generate polymer-based nanoporous spheres following removal of the silica template [69]. 

The porous membrane templates described above do exhibit three-dimensionality, but with limited interconnectedness between the discrete tubelike structures. Porous structures with more integrated pore—solid architectures can be designed using templates assembled from discrete solid objects or su-pramolecular structures. One class of such structures are three-dimensionally ordered macroporous (or 3-DOM) solids, which are a class of inverse opal structures. The design of 3-DOM structures is based on the initial formation of a colloidal crystal composed of monodisperse polymer or silica spheres assembled in a close-packed arrangement. The interconnected void spaces of the template, 26 vol % for a face-centered-cubic array, are subsequently infiltrated with the desired material. 

Various theories have been proposed to describe the transport in all of these types of polymer membranes. Theories for macroporous and microporous membranes have been based on hydrodynamic and frictional considerations while those for nonporous gels have been based on Eyring s theory and use a free volume approach to describe the movement of solute through the mesh of the polymer. 

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]. 

Because the mechanisms are based on pore flow and size exclusion (cf. Section 2.2), the polymer material itself does not have direct influence on flux and selectivity in U F. The U F membranes usually have an integrally asymmetric structure, obtained via the NIPS technique, and the porous selective barrier (pore size and thickness ranges are 2-50 nm and 0.1-1 (im, respectively) is located at the top (skin) surface supported by a macroporous sublayer (cf. Section 2.4.2). However, the pore-size distribution in that porous barrier is typically rather broad (Figure 2.6), resulting in limited size selectivity. 

Abstract. The constructive and technological features of silicon electrodes of polymer electrolyte membrane fuel cell (PEMFC) are discussed. Electrodes are made with application of modem technologies of integrated circuits, and technologies of macroporous silicon. Also ways of realization of additional functionalities of electrodes to offered constructive - technological performance are considered. 

A polymer membrane employed in water aeration device is a typical example of macroporous membranes, i.e., membranes with sub-millimeter holes. A rubber film with numbers of slits functions as a thin layer that separates the gas phase and the liquid phase, which allows the transfer of the gas into the liquid phase in a controlled manner. Such a film is appropriately termed as aeration membrane. 

Chen X, Liu JH, Feng ZC, and Shao ZZ. Macroporous chitosan/carboxymethylclellulose blend membranes and their application for lysozyme adsorption. J. Appl. Polym. Sci. 2005 96 1267-1274. 

Digestion can also be achieved using a trypsin IMER, where trypsin is immobilized to a solid support, e.g, macroporous silica [38], on POROS material (Porozyme IMER) [39-40], a PVDF membrane in a microreactor [41], or silica-based [42] or porous polymer monoliths [43-45]. 

Synthesis routes are reviewed for preparation of polymers from styrene, divinylbenzene (and possibly functionalized monomers) to give membranes, gel-form beads, and macroporous beads. Methods are summarized for functionalization of these polymers to give pendent groups such as -Br and -CH2CI, which can be converted into ligands such as -PPI12, -NR2>... 

Rao and Sircar [80] developed a new technique. A macroporous graphite sheet was coated with a suitable polymer (latex) which was pyrolysed subsequently. This process was repeated 4-5 times and resulted in a carbon layer thickness of 2.5 pm with an average pore diameter between 0.5 and 0.6 nm. The membrane has interesting properties (see Chapter 9). 

An overview of microporous membrane types is given in Table 9.4. The oldest microporous membranes are based on carbon and are reported by Koresh and Softer in a series of papers from 1980 to 1987 (see overviews in Refs. [6,42]). They are made by pyrolysis of a suitable polymer (hollow fibre) as reviewed by Burggraaf and Keizer [9]. More recently Rao and Sircar [42] developed a new technique. A macroporous graphite sheet was coated with a suitable polymer (latex) which was pyrolysed subsequently. This process was repeated 4—5 times and resulted in a total carbon layer thickness of 2.5 pm with an average pore diameter between 0.5 and 0.6 nm. The membrane has interesting properties (see Section 9.4.3). 

This is a combined organic-inorganic membrane that comprises a macropor-ous a-alumina substrate (tubular or multichannel), an intermediate mesopor-ous inorganic titanium oxide layer (thickness 1 pm) and a microporous Nafion polymer top-layer (thickness less than 0.1 pm). The overall performance and... 

Several investigators have demonstrated the feasibility of immobilized liquid membrane gas separations in applications where large pressure differences are encountered such as acid gas removal from synthetic natural gas. The immobilized liquid membranes prepared by Kimura et al. (16) using 100 pm cellulose acetate supports withstood CO2 partial pressure differences of up to 6.89 10 N/m. Matson et al. (15) used mlcroporous cellulose acetate and polyethersulfone films of 25-75 pm thickness to successfully immobilize potassium carbonate solutions for H2S transport at pressure differences of up to 2.07 10 N/m. The ILMs were supported by macroporous non-wetting polymer films such as polypropylene and polytetrafluoro-ethylene to increase the resistance to high transmembrane pressures. 

The membrane shown in Fig. 4.10 was prepared using this three-dimensionally ordered macroporous polyimide obtained according to the above process with AMPS polymer. The proton conductivity and methanol permeability of the composite membrane are summarized in Table 4.2. The proton conductivity of the composite membrane was higher than that of Nafion and the methanol permeability of the composite membrane was slightly lower than that of Nafion . Both tendencies are good for membrane for direct methanol fuel cell. In this way, three-dimensionally ordered macroporous materials are suitable for matrix of soft proton conductive polymer with higher proton conductivity. 

Fig. 4.10 Photograph and scanning electron micrograph of three-dimensionaUy ordered macro-porous polyimide and composite membrane consisting of macroporous polyimide and proton conductive polymer...

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