Clustering of Ions in Organic Polymers. A Theoretical Approach
TL;DR: In this article, the maximum size of a non-crystalline and approximately spherical multiplet is determined by the surface areas and volumes of the participating chemical species and is of the order of 8 ion pairs or less.
Abstract: : Clustering of ions in organic polymers is treated from a theoretical point of view. It is shown that ions in organic media of low dielectric constant exist most probably as pairs or higher multiplets, even at relatively high temperatures. The maximum size of a non-crystalline and approximately spherical multiplet is shown to be determined by the surface areas and volumes of the participating chemical species and is of the order of 8 ion pairs or less. At relatively low temperatures, the ionic multiplets can aggregate to form a cluster, the factors involved in cluster formation being the elasticity of the chains and the electrical work of cluster collapse. Several simple geometries are assumed for ethylene-sodium methacrylate clusters, and the average inter-cluster distance for 4.5 mol % of the ionic component ranges from 44A to 95A. The experimentally determined repeat distance is of the order of 83A. (Author)
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TL;DR: In this comprehensive review, recent progress and developments on perfluorinated sulfonic-acid (PFSA) membranes have been summarized on many key topics, including structure/transport correlations and modeling, composite PFSA membranes, degradation phenomena, and PFSA thin films.
Abstract: In this comprehensive review, recent progress and developments on perfluorinated sulfonic-acid (PFSA) membranes have been summarized on many key topics. Although quite well investigated for decades, PFSA ionomers’ complex behavior, along with their key role in many emerging technologies, have presented significant scientific challenges but also helped create a unique cross-disciplinary research field to overcome such challenges. Research and progress on PFSAs, especially when considered with their applications, are at the forefront of bridging electrochemistry and polymer (physics), which have also opened up development of state-of-the-art in situ characterization techniques as well as multiphysics computation models. Topics reviewed stem from correlating the various physical (e.g., mechanical) and transport properties with morphology and structure across time and length scales. In addition, topics of recent interest such as structure/transport correlations and modeling, composite PFSA membranes, degradat...
1,217 citations
TL;DR: In this paper, the authors summarized the nature of the global water problem and reviewed the state of the art of membrane technology and identified existing deficiencies of current membranes and the opportunities to resolve them with innovative polymer chemistry and physics.
Abstract: Two of the greatest challenges facing the 21st century involve providing sustainable supplies of clean water and energy, two highly interrelated resources, at affordable costs. Membrane technology is expected to continue to dominate the water purifica- tion technologies owing to its energy efficiency. However, there is a need for improved membranes that have higher flux, are more selective, are less prone to various types of fouling, and are more resistant to the chemical environment, especially chlorine, of these processes. This article summarizes the nature of the global water problem and reviews the state of the art of membrane technology. Existing deficiencies of current membranes and the opportunities to resolve them with innovative polymer chemistry and physics are identified. Extensive background is provided to help the reader understand the fundamental issues involved. V C 2010 Wiley Periodi- cals, Inc. J Polym Sci Part B: Polym Phys 48: 1685-1718, 2010
821 citations
TL;DR: This review has highlighted the important effects that should be modeled and shown the vast complexities of transport within polymer-electrolyte fuel cells and the various ways they have been and can be modeled.
Abstract: In this review, we have examined the different models for polymer-electrolyte fuel cells operating with hydrogen. The major focus has been on transport of the various species within the fuel cell. The different regions of the fuel cell were examined, and their modeling methodologies and equations were elucidated. In particular, the 1-D fuel-cell sandwich was discussed thoroughly because it is the most important part of the fuel-cell assembly. Models that included other effects such as temperature gradients and transport in other directions besides through the fuel-cell sandwich were also discussed. Models were not directly compared to each other; instead they were broken down into their constitutive parts. The reason for this is that validation of the models is usually accomplished by comparison of simulation to experimental polarization data (e.g., Figure 3). However, other data can also be used such as the net flux of water through the membrane. In fitting these data, the models vary not only in their complexity and treatments but also in their number and kind of fitting parameters. This is one reason it is hard to justify one approach over another by just looking at the modeling results. In general, it seems reasonable that the more complex models, which are based on physical arguments and do not contain many fitting parameters, are perhaps closest to reality. Of course, this assumes that they fit the experimental data and observations. This last point has been overlooked in the validation of many models. For example, a model may fit the data very well for certain operating conditions, but if it does not at least predict the correct trend when one of those conditions is changed, then the model is shown to be valid only within a certain operating range. This review has highlighted the important effects that should be modeled. These include two-phase flow of liquid water and gas in the fuel-cell sandwich, a robust membrane model that accounts for the different membrane transport modes, nonisothermal effects, especially in the directions perpendicular to the sandwich, and multidimensional effects such as changing gas composition along the channel, among others. For any model, a balance must be struck between the complexity required to describe the physical reality and the additional costs of such complexity. In other words, while more complex models more accurately describe the physics of the transport processes, they are more computationally costly and may have so many unknown parameters that their results are not as meaningful. Hopefully, this review has shown and broken down for the reader the vast complexities of transport within polymer-electrolyte fuel cells and the various ways they have been and can be modeled.
649 citations
TL;DR: Nemat-Nasser and Hori as mentioned in this paper developed a micromechanical model which accounts for the coupled ion transport, electric field, and elastic deformation to predict the response of the IPMC, qualitatively and quantitatively.
Abstract: An ionic polymer-metal composite (IPMC) consisting of a thin Nafion sheet, platinum plated on both faces, undergoes large bending motion when an electric field is applied across its thickness. Conversely, a voltage is produced across its faces when it is suddenly bent. A micromechanical model is developed which accounts for the coupled ion transport, electric field, and elastic deformation to predict the response of the IPMC, qualitatively and quantitatively. First, the basic three-dimensional coupled field equations are presented, and then the results are applied to predict the response of a thin sheet of an IPMC. Central to the theory is the recognition that the interaction between an imbalanced charge density and the backbone polymer can be presented by an eigenstress field (Nemat-Nasser and Hori, Micromechanics, Overall Properties of Heterogeneous Materials, 2nd Ed., Elsevier, Amsterdam, 1999). The constitutive parameter connecting the eigenstress to the charge density is calculated directly using a s...
597 citations
TL;DR: In this article, a comparison of metal-plated and bare Nafion and Flemion in various ion forms and various water saturation levels has been performed in the author's laboratories at the University of California, San Diego.
Abstract: Ionic polymer-metal composites (IPMCs) consist of a polyelectrolyte membrane (usually, Nafion or Flemion) plated on both faces by a noble metal, and is neutralized with certain counter ions that balance the electrical charge of the anions covalently fixed to the backbone membrane. In the hydrated state (or in the presence of other suitable solvents), the composite is a soft actuator and sensor. Its coupled electrical-chemical-mechanical response depends on: (1) the chemical composition and structure of the backbone ionic polymer; (2) the morphology of the metal electrodes; (3) the nature of the cations; and (4) the level of hydration (solvent saturation). A systematic experimental evaluation of the mechanical response of both metal-plated and bare Nafion and Flemion in various cation forms and various water saturation levels has been performed in the author’s laboratories at the University of California, San Diego. By examining the measured stiffness of the Nafion-based composites and the corresponding bare Nafion, under a variety of conditions, I have sought to develop relations between internal forces and the resulting stiffness and deformation of this class of IPMCs. Based on these and through a comparative study of the effects of various cations on the material’s stiffness and response, I have attempted to identify potential micromechanisms responsible for the observed electromechanical behavior of these materials, model them, and compare the model results with experimental data. A summary of these developments is given in the present work. First, a micromechanical model for the calculation of the Young modulus of the bare Nafion or Flemion in various ion forms and water saturation levels is given. Second, the bare-polymer model is modified to include the effect of the metal plating, and the results are applied to calculate the stiffness of the corresponding IPMCs, as a function of the solvent uptake. Finally, guided by the stiffness modeling and data, the actuation of the Nafion-based IPMCs is micromechanically modeled. Examples of the model results are presented and compared with the measured data.
507 citations
Cites background from "Clustering of Ions in Organic Polym..."
...The anions (sulfonates or carboxylates) within the clusters are covalently attached to the fluorocarbon matrix, while in a hydrated state the associated unbound cations can move within the water that permeates the interconnected clusters [Eisenberg, 1970; Gierke et al., 1981; Hsu and Gierke, 1982; Mauritz, 1988; Xue et al., 1989; Lee et al., 1992; Heitner-Wirguin, 1996; Li and Nemat-Nasser, 2000; and Nemat-Nasser and Li, 2000]....
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...…fluorocarbon matrix, while in a hydrated state the associated unbound cations can move within the water that permeates the interconnected clusters [Eisenberg, 1970; Gierke et al., 1981; Hsu and Gierke, 1982; Mauritz, 1988; Xue et al., 1989; Lee et al., 1992; Heitner-Wirguin, 1996; Li and…...
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