Development of polymer membrane

Development of Polymer Membrane Anion-Selective Electrodes Based on Molecular Recognition Principles... 

In this paper, we report the development of ISEs that have been designed by using molecular recognition principles. Specific examples include the development of polymer membrane anion-selective electrodes based on hydrophobic vitamin B12 derivatives and a cobalt porphyrin. The selectivity patterns observed with these electrodes can be related to differences in the structure of the various ionophores, and to properties of the polymer film. 

In summary, it has been demonstrated that ISEs can be designed by employing molecular recognition principles. In particular, the feasibility of using hydrophobic vitamin B12 derivatives and electropolymerized porphyrin films in the development of polymer membrane anion-selective electrodes has been demonstrated. The studies indicated that the changes in the selectivity of these ISEs can be explained by the difference in structure of the ionophores. In addition, it was shown that by electropolymerization of a cobalt porphyrin, anion-selective electrodes can be prepared that have extended lifetimes compared with PVC-based ISEs, which use a similar compound as the ionophore. 

This introductory chapter provides a brief outline and history of the PEFC technology, and important requirements and aspects in the development of polymer membranes for fuel cells. To obtain materials that meet specific requirements, the relationship of composition/structure and the properties has to be estabUshed. For the preparation of the membrane electrode assembly, it is important to understand the interfacial properties between membrane and electrodes. 

Clearly, a better understanding of the gas transport mechanisms in polymers would greatly facilitate the development of polymer membranes that exhibit both a higher selectivity and a higher (or lower) permeability to specified gases. It is beyond the scope of the present chapter to review this area of research, particularly since a number of extensive reviews are available [1,3-9,11-15,17,18]. 

Sollner, K., The early developments of the electrochemistry of polymer membranes, in Charged Gells and Membranes (Ed. E. Selegny), Vol. 1, Reidel, Dordrecht, 1976. 

The development of anisotropic membranes based on a hydrophobic polymer matrix (e.g., polysulfone derivatives or phosphonylated-PPO) which does not collapse upon drying, made possible a more thorough investigation into the origin and role of the nodular layer. It is now clear that if the nodular layer extends to the interface without fusion, the membrane is open to solute permeation. Solute separation would then be dependent upon the serriedness of the nodules... 

Recent research in the field of polymer membrane ion-selective electrodes [389-391], has revealed that their se-lectivities [392-396] and limits of detections [394-397] could be improved by several orders of magnitude. The review of Bakker and Pretsch [398] summarized recent progress in the development and application of potentiometric sensors with low detection limit in the range 10-8-10-11 M. 

Using proton exchange membranes as electrolytes that are quasi-solid may cause a problem with respect to the perfect wetting of the catalyst particles. In spite of this (initial) difficulty of developing solid polymer membrane fuel cells, water-swollen perfluorinated sulfonic acid polymers such as the commercial Nation have been used for fuel cells very early since they offer the following advantages ... 

The need for operation at high temperatures has already been mentioned. A higher operating temperature would reduce the size of the heat rejection equipment. In addition, operation at >100°C would greatly simplify water management inside the fuel cell because all water inside the fuel cell would be in vapor phase. The challenge is to develop a polymer membrane that can operate at high temperature. 

The values of permeability coefficients for He, O2, N2, CO2, and CH4 in a variety of dense (isotropic) polymer membranes and the overall selectivities (ideal separation factors) of these membranes to the gas pairs He/N2,02/N2, and CO2/CH4 at 35°C have been tabulated in numerous reviews (Koros and Heliums, 1989 Koros, Fleming, and Jordan et al., 1988 Koros, Coleman, and Walker, 1992). Moreover, several useful predictive methods exist to allow estimation of gas permeation through polymers, based on their structural repeat units. The values of the permeability coefficients for a given gas in different polymers can vary by several orders of magnitude, depending on the nature of the gas. Thevalues oftheoverall selectivities vary by much less. Particularly noteworthy is the fact that the selectivity decreases with increasing permeability. This is the well-known inverse selectivity/permeability relationship of polymer membranes, which complicates the development of effective membranes for gas separations. 

New catalysts of hydrogen oxidation for low-temperature fuel cells are molybdenum and tungsten carbides [2, 3], For solid polymeric fuel cells the novel catalysts by plasma treatment of polymer membrane have been developed. The radicals at surface are generated. These radicals are catalysts of anodic reactions [4]... 

The development of asymmetric membrane technology in the 1960 s was a critical point in the history of gas separations. These asymmetric structures consist of a thin (0.1 utol n) dense skin supported on a coarse open-cell foam stmcture. A mmetric membranes composed of the polyimides discussed above can provide extremely high fluxes throuj the thin dense skin, and still possess the inherently hij separation factors of the basic glassy polymers from which they are made. In the early 1960 s, Loeb and Sourirajan described techniques for producing asymmetric cellulose acetate membranes suitable for separation operations. The processes involved in membrane formation are complex. It is believed that the thin dense skin forms at the... 

A significant number of works are concerned with the development of new membranes for the separation of mixtures of aromatic/alicyclic hydrocarbons [10,11,77-109]. For example, the following works can be mentioned. A mixture of cellulose ester and polyphosphonate ester (50 wt%) was used for benzene/cyclohexane separation [113]. High values of the separation factor and flux were achieved (up to 2 kg/m h). In order to achieve better fluxes and separation factors the attention was shifted to the modification of polymers by grafting technique. Grafted membranes were made of polyvinylidene fluoride with 4-vinyl pyridine or acrylic acid by irradiation [83]. 2-Hydroxy-3-(diethyl-amino) propyl methacrylate-styrene copolymer membranes with cyanuric chloride were prepared, which exhibited a superior separation factor /3p= 190 for a feed aromatic component concentration of 20 wt%. Graft copolymer membranes based on 2-hydroxyethyl methylacrylate-methylacrylate with thickness 10 pm were prepared [85]. The membranes yielded a flux of 0.7 kg/m h (for feed with 50 wt% of benzene) and excellent selectivity. Benzene concentration in permeate was about 100 wt%. A membrane based on polyvinyl alcohol and polyallyl amine was prepared [87]. For a feed containing 10 wt% of benzene the blend membrane yielded a flux of 1-3 kg/m h and a separation factor of 62. 

Kusumocahyo, S.P., Kanamori, T., Sumaru, K., Aomatsu, S., Matsuyama, H., Teramoto, M., and Shinbo, T., Development of polymer inclusion membranes based on cellulose triacetate Carrier-mediated transport of cerium(III). J. Membr. Sci., 2004, 244 251-257. 

Li, Q. He, R. Jensen, J.O. Bjerrum, N.J. Approaches and recent development of polymer electrolyte membranes for fuel cells operating above 100°C. Chem. Mater. 2003, 15, 4896. 

Following a brief review of the development of dynamic membranes and an overview of the current state of the art, Spencer (10) discusses dynamic polyblend membranes. In particular, he looks at the Influence that polymer selection and membrane preparation procedures have on membrane performance. Dynamic membranes composed of a poly(acrylic acid)/basic polyamine blend deposited on a ZOSS (hydrous zirconium oxide on stainless steel) ultrafiltration membrane are discussed. Their hyperfiltration or reverse osmosis properties are compared to the more traditional ZOPA (zirconium oxide plus poly(acrylic acid)) membrane. 

While the majority of enzyme electrodes fabricated have been rather large devices, there have been some recent reports concerning the development of miniaturized and even microsensors. For example, MeyerhoflF (M5) prepared an essentially disposable urea sensor (tip diameter 3 mm) by immobilizing urease at the surface of a new type of polymer-membrane electrode-based ammonia sensor (see Fig. 4). Alexander and Joseph (Al) have also prepared a new miniature urea sensor by immobilizing urease at the surface of pH-sensitive antimony wire. Similarly, lannello and Ycynych (II) immobilized urease on a pH-sensitive iridium dioxide electrode. In these latter investigations, ammonia liberated from the enzyme-catalyzed reaction alters the pH in the thin film of enzyme adjacent to the pH-sensitive wire. 

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