Semipermeable polymeric membrane

A straightforward way to collect solutes from the interstitial fluid (ISF) space would be to have a semipermeable, hollow fiber, membrane-based device as originally described by Bito et al.1 Two semipermeable membrane-based devices that have been used to collect different types of analytes from various mammalian tissues include microdialysis sampling probes (catheters) and ultrafiltration probes. The heart of each of these devices is the semipermeable polymeric membrane shown in Figure 6.1. The membranes allow for collection of analytes from the ISF that are below the membrane molecular weight cutoff (MWCO). Each of these devices provides a sample that has a significantly reduced amount of protein when compared to either blood or tissue... 

Ultrafiltration membrane process. In this process, pressure is used to obtain a separation of molecules by a semipermeable polymeric membrane (M2). The membrane discriminates on the basis of molecular size, shape, or chemical structure and separates relatively high molecular weight solutes such as proteins, polymers, colloidal materials such as minerals, and so on. The osmotic pressure is usually negligible because of the high molecular weights. This is covered in Section 13.11. 

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. 

Figure 8.34 Examples of drug-delivery systems employing polymeric membranes, (o) Ocusert system for the eye with two rote-controlling membranes, (b) Tronsiderm system for transdermal medication with one rote-controlling layer, (c) The Progestasert device for intrauterine insertion in which the body of the device serves as the rote-controlling barrier, (d) The oral Oros device in which the membrane is o semipermeable membrane which forbids drug transport, allowing water ingress only.

There are essentially four different types of membranes, or semipermeable barriers, which have either been commercialized for hydrogen separations or are being proposed for development and commercialization. They are polymeric membranes, porous (ceramic, carbon, metal) membranes, dense metal membranes, and ion-conductive membranes (see Table 8.1). Of these, only the polymeric membranes have seen significant commercialization, although dense metal membranes have been used for commercial applications in selected niche markets. Commercial polymeric membranes may be further classified as either asymmetric (a single polymer composition in which the thin, dense permselective layer covers a porous, but thick, layer) or composite (a thick, porous layer covered by a thin, dense permselective layer composed of a different polymer composition).2... 

Besides the synthesis of bulk polymers, microreactor technology is also used for more specialized polymerization applications such as the formation of polymer membranes or particles [119, 141-146] Bouqey et al. [142] synthesized monodisperse and size-controlled polymer particles from emulsions polymerization under UV irradiation in a microfluidic system. By incorporating a functional comonomer, polymer microparticles bearing reactive groups on their surface were obtained, which could be linked together to form polymer beads necklaces. The ability to confine and position the boundary between immiscible liquids inside microchannels was utilized by Beebe and coworkers [145] and Kitamori and coworkers [146] for the fabrication of semipermeable polyamide membranes in a microfluidic chip via interfacial polycondensation. 

The research of Wolter et al. (2004) was related to the development of semiperme-able membranes comprising organically modihed silicic acid polycondensates and a process for preparing them for their use in gas exchange and in separation techniques, especially in gas separation, dialysis, and PV. The membranes of their invention can be flat or tubular. The membranes are cured by addition polymerization or polyaddition of the C=C double bonds. 

SLMs containing selective carriers (ionophores) give higher fluxes and selec-tivities than conventional semipermeable porous polymeric membranes, because diffusion is faster in liquids than in solids. The carrier dissolved in the liquid membrane favours the distribution of one species out of a mixture by specific complexation and extraction, if properly chosen [9]. 

A potentiometric sensor was developed by Martinez-Manez and co-workers in thick film technology. Ru02 was used as sensitive material whereas this active electrode surface was covered with a semipermeable polymeric (poly-isophthalamide diphenylsulfone, PIDS) or ceramic-based (Ti02) membrane. The measurement of DO could only be carried out effectively if other redox processes were excluded except the desired reaction which was produced by oxygen. This was achieved by covering the active electrode with a semipermeable polymeric or ceramic membrane which allowed to pass DO and excluded any other redox-active species present in solution. A schematic view of the DO potentiometric sensor is displayed in Fig. 3.2. 

Adsorption systems employing molecular sieves are available for feed gases having low acid gas concentrations. Another option is based on the use of polymeric, semipermeable membranes which rely on the higher solubiHties and diffusion rates of carbon dioxide and hydrogen sulfide in the polymeric material relative to methane for membrane selectivity and separation of the various constituents. Membrane units have been designed that are effective at small and medium flow rates for the bulk removal of carbon dioxide. 

Osmosis is the passage of a pure solvent into a solution separated from it by a semipermeable membrane, which is permeable to the solvent but not to the polymeric solute. The osmotic pressure n is the pressure that must be applied to the solution in order to stop the flow. Equilibrium is reached when the chemical potential of the solvent is identical on either side of the membrane. The principle of a membrane osmometer is sketched in Figure 2. 

This concentration method uses a polymeric semipermeable membrane and principles of RO to effect separation of water from the organics in drinking water samples. In this process, a water sample is recirculated past the semipermeable membrane while hydraulic pressures exceeding the osmotic pressure are maintained. Water is transported through the membrane under these conditions (permeation). The concentration of solutes continues to build as water is removed from the system. 

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