Polymers and Polymeric Membranes

Creative interplay between colloid and polymer chemistries has increasingly contributed to the development of membrane-mimetic systems and advanced materials. On the one hand, the employment of polymer methodologies and/or the addition of polymers have favorably altered the properties of colloidal systems. On the other hand, the introduction of surfactants and surfactant assemblies prior, during, or subsequent to polymerization has resulted in distinctly different polymers. 

Incorporation of polymerizable moieties into surfactants or into their counterions has permitted the formation of polymerized or polymer-coated 

The removal of surfactants from polymer-coated vesicles and from composite cast bilayers to yield ghost vesicles and molecularly thick, two-dimensional polymer networks (detailed previously) illustrates a colloid-chemical approach to the construction of specific polymers. 

The inter-relationship between colloid and polymer chemistries is completed by colloidal polymer particles. The formation of 50-nm-diameter, 100- to 200-nm-long polyaniline fibrils in a poly(acrylic acid)-template-guided polymerization, similar in many ways to those produced from polymerized SUVs (see above), provides a recent example of polymer colloids [449], The use of poly(styenesulfonic acid) as a template yielded globular polyaniline particles which were found to be quite different morphologically from those observed in the regular chemical synthesis of polyaniline [449]. 

Many aspects of the chemical behavior of colloids are also exhibited by polymer gels [450,451]. Certain polymers which possess the appropriate three-dimensional networks may increase their size several fold, as do colloids, by 

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Polyions, polymers, and polymeric membranes also provide suitable compartments for semiconductor particles and particulate films [668-682]. With improved chemical and physical methodologies, polymer chemists will soon be able to construct supramolecular, dimensionally controlled assemblies which will rival the sophistication of LB and SA films. 

To develop such a method, a physical model for the "active" portion of the meiri>rane of interest is necessary. Membrane models that have been developed previously for various purposes have been reviewed elsewhere (see for example References and. A slightly different model is being proposed in this paper this model is based on a number of experimental observations on polymers and polymeric membranes, some of which are summarized below ... 

Estimation of free-volume parameters for solvent and polymeric membranes Six parameters (three for each solvent and three for the polymer) were estimated using the following theories (a) PDMS (K22 - Tg2> and K22/Y were obtained in literature (Hong, 1995) using polymer viscosity and temperature data. This procedure is expressed in terms of the Williams-Landel-Ferry equation (Williams et al., 1955). The polymer s free volume parameter was related to the Williams-Landel-Ferry constants as presented in equation (2). (b) The same approach was used to obtain (K22 - Tg2) and K22/Y for POMS (equation (2)), but zero shear viscosity data prediction was required prior to this step, (c) EB and Water (K21 - Tgj) and K21/Y parameters were calculated for both components using pure component data of viscosity and temperature (Djojoputro and Ismadji, 2005). Hong (1995) presented equation (3) where free volume... 

Enzymes are covalently immobilized primarily onto the surface of the membrane exposed to the feed solution, known as the "active side" of the asymmetric membrane. In general, it is not clear whether reaction between enzymes and polymeric membranes via coupling agents simply results in enzyme attachment to the membrane, or if it leads to an enzyme-carrier network inside the polymer matrix. For the sake of simplicity let us assume that asymmetric membranes are used, that suitable active groups are available on the polymeric surface and that the membrane molecular weight cut-off is such that the active layer is enzyme-impermeable. In this way, even though their activity is often drastically reduced, surface bound enzymes are in close proximity to the substrate solution-thus reducing the mass transfer resistance to that associated with the boundary layer. When enzymes are covalently immobilized in the... 

Sikdar et al. (2000) developed adsorbent-filled PV membranes for removing VOCs from waste water. These membranes were prepared by dispersing at least one hydrophobic adsorbent uniformly into a polymer matrix. Polymeric membrane was made of rubbery polymer selected from the group consisting of PDMSs, PTMSP, PUs, polycarbonates (PCs), PE-block-polyamides, silicon PCs, styrene butadiene rubber, nitrile butadiene rubber, and ethane-propene terpolymer. The hydrophobic adsorbent was selected from the group consisting of hydrophobic zeolites, hydrophobic molecular sieves, activated carbon, hydrophobic polymer resin adsorbents, and mixtures thereof. 

The application tests of hyperbranched polymers have namely focused on their employment as non-linear optical polymers, polymer electrolytes, biomaterials, supramolecular components (nanomaterials), photolithographic materials, coatings, modifiers and additives and polymeric membranes so far [3]. 

Sustainable and controlled syntheses of polymers and polyelectrolyte membranes have been carried out in IL/O microemulsions, where the corresponding monomeric organic compounds constitute the oil phase. For example, Yan and coworkers used MMA/[Cj2mim][Cl]/[bmim][BFJ microemulsion to carry out atom transfer radical polymerization (ATRP) reaction to generate polymethyl methacrylate (PMMA) [133]. When this reaction was carried out in conventional microemulsions, large quantity of surfactants was needed to stabilize these systems, which rendered the... 

AF-FFF is a powerful technique, especially for size determination in aqueous solution. " It was introduced in 1987 by Wahlund et al. and since then has become increasingly popular, for example, for the characterization of polymers and polymeric partides. " In addition, several examples have been reported demonstrating the ability of AF-FFF to be employed also in organic solution. The major challenge here is the stability of the membranes used, which usually consist of commonly used membranes known from ultrafiltration... 

Interfacial polymerization membranes are less appHcable to gas separation because of the water swollen hydrogel that fills the pores of the support membrane. In reverse osmosis, this layer is highly water swollen and offers Httle resistance to water flow, but when the membrane is dried and used in gas separations the gel becomes a rigid glass with very low gas permeabiUty. This glassy polymer fills the membrane pores and, as a result, defect-free interfacial composite membranes usually have low gas fluxes, although their selectivities can be good. 

Polymeric Ma.teria.Is, The single-ply membranes are made from a wide variety of polymers. The following is a brief description of those polymers and their characteristics. There are three thermosetting-type elastomeric membranes as of this writing (1996) neoprene, CSPE, and EPDM. Neoprene is stiU used where oil resistance is needed. Eor instance. Hydrotech uses neoprene flashings, the base of which is hot-set in mbberized asphalt (see ElASTOL RS, SYNTHETIC-POLYCm.OROPRENE). 

By the time the next overview of electrical properties of polymers was published (Blythe 1979), besides a detailed treatment of dielectric properties it included a chapter on conduction, both ionic and electronic. To take ionic conduction first, ion-exchange membranes as separation tools for electrolytes go back a long way historically, to the beginning of the twentieth century a polymeric membrane semipermeable to ions was first used in 1950 for the desalination of water (Jusa and McRae 1950). This kind of membrane is surveyed in detail by Strathmann (1994). Much more recently, highly developed polymeric membranes began to be used as electrolytes for experimental rechargeable batteries and, with particular success, for fuel cells. This important use is further discussed in Chapter 11. 

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