Membranes conductive polymers

Gas separation membranes, conducting polymer applications, 7 539 Gas-solid chromatography, adsorption,... 

In some cases, conducting polymer-based ion-selective membranes can substitute the commonly used plasticized PVC-based ion-selective (liquid) membranes. However, there are fundamental differences between the two types of membranes. Conducting polymer membranes are most often non-plasticized and the charge is transported by both... 

Practical appHcations have been reported for PVP/ceUulosics (108,119,120) and PVP/polysulfones (121,122) in membrane separation technology, eg, in the manufacture of dialysis membranes. Electrically conductive polymers of polyaruline are rendered more soluble and hence easier to process by complexation with PVP (123). Addition of small amounts of PVP to nylon 66 and 610 causes significant morphological changes, resulting in fewer but more regular spherulites (124). 

A completely separate family of conducting polymers is based on ionic conduction polymers of this kind (Section 11.3.1.2) are used to make solid electrolyte membranes for advanced batteries and some kinds of fuel cell. 

The presence of polymer, solvent, and ionic components in conducting polymers reminds one of the composition of the materials chosen by nature to produce muscles, neurons, and skin in living creatures. We will describe here some devices ready for commercial applications, such as artificial muscles, smart windows, or smart membranes other industrial products such as polymeric batteries or smart mirrors and processes and devices under development, such as biocompatible nervous system interfaces, smart membranes, and electron-ion transducers, all of them based on the electrochemical behavior of electrodes that are three dimensional at the molecular level. During the discussion we will emphasize the analogies between these electrochemical systems and analogous biological systems. Our aim is to introduce an electrochemistry for conducting polymers, and by extension, for any electrodic process where the structure of the electrode is taken into account. 

Figure 13. Schematic diagram of the measurement of the ionic conductivity of a conducting polymer membrane as a function of oxidation state (potential), (a) Pt electrodes (b) potentiostat (c) gold minigrid (d) polymer film (e) electrolyte solution (0 dc or ac resistance measurement.133 (Reprinted with permission from J. Am Chem Soc. 104, 6139-6140, 1982. Copyright 1982, American Chemical Society.)...

Another method to synthesize hollow nanocapsules involves the use of nanoparticle templates as the core, growing a shell around them, then subsequently removing the core by dissolution [30-32]. Although this approach is reminiscent of the sacrificial core method, the nanoparticles are first trapped and aligned in membrane pores by vacuum filtration rather than coated while in aqueous solution. The nanoparticles are employed as templates for polymer nucleation and growth Polymerization of a conducting polymer around the nanoparticles results in polymer-coated particles and, following dissolution of the core particles, hollow polymer nanocapsules are obtained. 

The new edition of Principles of Electrochemistry has been considerably extended by a number of new sections, particularly dealing with electrochemical material science (ion and electron conducting polymers, chemically modified electrodes), photoelectrochemistry, stochastic processes, new aspects of ion transfer across biological membranes, biosensors, etc. In view of this extension of the book we asked Dr Ladislav Kavan (the author of the section on non-electrochemical methods in the first edition) to contribute as a co-author discussing many of these topics. On the other hand it has been necessary to become less concerned with some of the classical topics the details of which are of limited importance for the reader. 

Ion-exchanger membranes with fixed ion-exchanger sites contain ion conductive polymers (ionomers) the properties of which have already been described on p. 128. These membranes are either homogeneous, consisting only of a polyelectrolyte that may be chemically bonded to an un-ionized polymer matrix, and heterogeneous, where the grains of polyelectrolyte are incorporated into an un-ionized polymer membrane. The electrochemical behaviour of these two groups does not differ substantially. 

Yoon el al. [112] reported an all-solid-state sensor for blood analysis. The sensor consists of a set of ion-selective membranes for the measurement of H+, K+, Na+, Ca2+, and Cl. The metal electrodes were patterned on a ceramic substrate and covered with a layer of solvent-processible polyurethane (PU) membrane. However, the pH measurement was reported to suffer severe unstable drift due to the permeation of water vapor and carbon dioxide through the membrane to the membrane-electrode interface. For conducting polymer-modified electrodes, the adhesion of conducting polymer to the membrane has been improved by introducing an adhesion layer. For example, polypyrrole (PPy) to membrane adhesion is improved by using an adhesion layer, such as Nafion [60] or a composite of PPy and Nafion [117],... 

Another problem that is common for all membrane-based solid-state sensors is the ill-defined membrane-metal interface. A large exchange current density is required to produce a reversible interface for a stable potentiometric sensor response. One approach to improving this interface is to use conducting polymers. Conducting polymers are electroactive n-conjugated polymers with mixed ionic and electronic conductivity. They... 

J.E. Zachara, R. Toczylowska, R. Pokrop, M. Zagorska, A. Dybko, and W. Wroblewski, Miniaturised all-solid-state potentiometric ion sensors based on PVC-membranes containing conducting polymers. Sens. Actuators B. 101, 207-212 (2004). 

Cyclic voltammetry was performed with the ADH-NAD-MB/polypyrrole electrode in 0.1 M phosphate buffer (pH 8.5) at a scan rate of 5 mV s l. The corresponding substrate of ADH caused the anodic current at +0.35 V vs. Ag/AgCl to increase. These results suggest a possible electron transfer from membrane-bound ADH to the electrode through membrane-bound NAD and MB with the help of the conductive polymer of polypyrrole. 

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