Polymeric membranes spacers

The typical spiral-wound membrane, as shown in Figure 4.20, consists of four layers wrapped around a central collection pipe membrane, spacer (providing a permeate channel), membrane, and a new spacer (providing a feed channel). The feed-side spacer acts as a turbulence promotor, whereas on the permeate side the flow is directed toward the central pipe. The spiral-wound membrane will typically be a polymeric composite material, and is much used also for liquid separation. The packing density of this type of module will depend on the channel height, but is usually within the range of 300-1000 m /m [1]. Several modules may be assembled in one pressure vessel. 

Swiss-roll cell This cell, shown in Figure 26.14, has been proposed for both electro-organic syntheses and wastewater treatment [29, 37, 38]. It is fabricated from a multilayer stack of the following sheet materials (a) a polymeric cathode spacer cloth or mesh, (b) a cathode mesh, (c) an ion-exchange membrane, (d) a polymeric anode spacer cloth or mesh, and (e) an anode mesh. These sheets are assembled in the sequence a-b-a-c-de-d-... 

Plate and frame Flat porous plates covered with polymeric membrane material are assembled together with alternate hollow spacers to produce a cross-flow system where feed moves through the annular spaces between adjacent membrane surfaces. Although now largely superseded by other designs, the plate and frame system is still available with membrane areas up to 80 m. ... 

LB Films of Polymeric Amphiphile. Since the first successful deposition of a polymeric LB film (61), there have been a large number of studies examining different stmctural parameters on the transferabiHty and stabiHty of the polymeric LB films (4). One interesting idea for polymers for LB films is the use of a spacer group (mosdy hydrophilic) to decouple the motion of the polymer from that of the Hpid membrane (62,63). Monolayers from a poljmier (10) having hydrophilic phosphate groups and a tetraethylene oxide spacer were used to link a glycerol diether to the polymer chain (63). 

Another kind of contact-active antimicrobial surface was achieved by tethering antimicrobial peptides to surfaces [62], If such peptides were exclusively membrane-active they could not work like in solution but would be immobilized via a polymeric spacer that could potentially cross the cell wall. The latter was demonstrated by the group of Dathe, who immobilized cationic antimicrobial peptides on PentaGels [63], Also, the well-known antimicrobial peptide magainin I... 

Polymerization of LB films, or deposition of LB films on polymers, offers the opportunity to impart to LB films a higher degree of mechanical integrity. However, preliminary work in this direction shows a conflict between the chainlike primary structure of the polymer and the well-organized supramo-lecular structure [15]. One possible solution may be the insertion of flexible spacers between the main chain polymer and the side chain amphiphile, a route also employed in liquid crystal polymers. These materials belong to an interesting class of two-dimensional polymers, of which there are few examples. These toughening techniques may eventually be applied to stabilize other self-assembled microstructures, such as vesicles, membranes, and microemulsions. 

Prepolymerized lipids form vesicles only if the disentanglement of the polymer main chain ( = hack hone) and the membrane forming side-chains is simplified hy a hydrophilic spacer between them . Efficient decouplings of the motions of the polymeric chain and the polymeric bilayer are thus achieved and stable liposomes with diameters of around 500 nm were formed upon ultrasonication (Figure 4.28a). Their bilayer showed a well-defined melting behaviour in DSC. The ionene polymer with C12, C16 and C20 intermediate chains also produced vesicles upon sonication (Figure 4.28b). Here, the amphiphilic main chain is obviously so simple that ordering to form membranes produces no problems whatsoever . ... 

Di(undecenyl)phosphoric acid, [CH2=CH(CH2)gO]2P(O)OH, (DUP) was found to have the necessary properties needed for a complexing agent to be polymerized within a membrane the ion exchange group is separated by a spacer... 

The hydrogel membrane is a copolymer of N-isopropylacrylamide (NIPA) doped with methacrylic acid (MAA) and cross-linked with small amounts of ethylene glycol dimethacrylate (EGDMA). The prepolymer solution containing the monomers at the desired concentrations is poured between two glass plates separated by a 250 pm spacer. Polymerization is initiated using a combination of ammonium persulfate as free radical generator and tetraethylene-methylenediamine as accelerator. 

Styrene monomers with phosphonic acid placed on side chains with different spacer length have been polymerized by a radical mechanism to obtain membranes with controlled water uptake at high ion exchange capacity (lEC) values. The proton conductivity of polymers containing ethyl and hc grl spacers between the polystyrene (PS) main chain and the phosphonic acid reached similar conductivity between 10 and 140 Although... 

---