Porous membranes membrane functions

J. Lee, A. Hirao, and S. Nakahama, "Polymerization of Monomers Containing Functional Silyl Groups. 5. Synthesis of New Porous Membranes with Functional Groups," Macromolecules. 21, 274-276 [1988]. 

Lee, J.S., Hirao, A., and Nakahama, S. (1988) Polymerization of monomers containing functional silyl groups. 5. Synthesis of new porous membranes with functional groups. Macromolecules, 21,274-XJ6. 

As the cell is discharged, Zn2+ ions are produced at the anode while Cu2+ ions are used up at the cathode. To maintain electrical neutrality, SO4- ions must migrate through the porous membrane,dd which serves to keep the two solutions from mixing. The result of this migration is a potential difference across the membrane. This junction potential works in opposition to the cell voltage E and affects the value obtained. Junction potentials are usually small, and in some cases, corrections can be made to E if the transference numbers of the ions are known as a function of concentration.ee It is difficult to accurately make these corrections, and, if possible, cells with transference should be avoided when using cell measurements to obtain thermodynamic data. 

The main emphasis in this chapter is on the use of membranes for separations in liquid systems. As discussed by Koros and Chern(30) and Kesting and Fritzsche(31), gas mixtures may also be separated by membranes and both porous and non-porous membranes may be used. In the former case, Knudsen flow can result in separation, though the effect is relatively small. Much better separation is achieved with non-porous polymer membranes where the transport mechanism is based on sorption and diffusion. As for reverse osmosis and pervaporation, the transport equations for gas permeation through dense polymer membranes are based on Fick s Law, material transport being a function of the partial pressure difference across the membrane. 

A separator is a porous membrane placed between electrodes of opposite polarity, permeable to ionic flow but preventing electric contact of the electrodes. A variety of separators have been used in batteries over the years. Starting with cedar shingles and sausage casing, separators have been manufactured from cellulosic papers and cellophane to nonwoven fabrics, foams, ion exchange membranes, and microporous flat sheet membranes made from polymeric materials. As batteries have become more sophisticated, separator function has also become more demanding and complex. 

Piletsky SA, Matuschewski H, Schedler U, Wilpert A, Piletska EV, Thiele TA, Ulbricht M. Surface functionalization of porous polypropylene membranes with molecularly imprinted polymers by photograft copolymerization in water. Macromolecules 2000 33 3092-3098. 

However, the variety of composite materials to be elaborated by the method is still barely explored. For example, bi- and multimetallic nanoparticles, included in different matrices (polymeric membranes, porous supports,. ..) or functionalized, have promising applications. New methods of cluster characterization at this extremely low size scale are developed and will improve their study. 

Kinoshita et alJ107,l0x used poly(L-glutamic acid) containing 12-14 mol% azobenzene units in the side chains (Scheme 3, Structure III) to prepare membranes obtained by coating a porous Millipore filter with a 0.2 % chloroform solution of III. Irradiation at 350 nm was found to increase the membrane potential and crossmembrane permeability. The photoinduced alterations of the membrane functions were completely reversible and could be controlled by irradiation and dark-adaptation, in correlation with the trans-cis photoisomerization of the azobenzene units. 

In order to predict correctly the fluxes of multicomponent mixtures in porous membranes, simplified models based solely on Fields law should be used with care [28]. Often, combinations of several mechanisms control the fluxes, and more sophisticated models are required. A well-known example is the Dusty Gas Model which takes into account contributions of molecular diffusion, Knudsen diffusion, and permeation [29]. This model describes the coupled fluxes of N gaseous components, Ji, as a function of the pressure and total pressure gradients with the following equation ... 

Fig. 8. Activity of immobilized antibody by the radiation polymerization method as a function of antigen concentration. Antigen a-fetoprotein. Antibody anti-a-fetoprotein. Immobilization method polymerization of HEMA in a thin porous membrane O polymerization of HEMA in particle form...

For solution diffusion, a drag reservoir is bound by a polymeric membrane which has a compact, non-porous structure and functions as a rate-controlling barrier (Figure 4.1). 

Other electrodes functioning in a similar way have been developed for other dissolved gases, with important clinical applications (Table 14.1). Since the porous membrane does not let past species that can poison the electrode, these electrodes are ideal for measurements in biological fluids. 

Fig. 7.7. Transient current response, 1 - exp(-kEi), as a function of time, and the biological layer thickness, Itq. The data indicate that the response is relatively insensitive to the thickness of the porous membrane (mtq = 0, top ntlq = 60, bottom), but sensitive to the diffusion barrier presented by the biological layer (DIDf= 1, left DIDf= 10, right). D =...

Figure 34.18 Water flux and salt rejection as functions of deposition time, in minutes, for composite membranes of acetylene/C0/H20 (CNCA porous membrane used as substrate).

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