Characterization of nafion® membranes by transmission electron microscopy

Xue, Tingting; Trent, John S.; Osseo‐Asare, K.

doi:10.1016/s0376-7388(00)80518-9

Cited by 97 publications

(74 citation statements)

References 17 publications

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“…The validity of such a structure has been supported by both theoretical (Eisenberg, 1970;Hsu and Gierke, 1982) and experimental (Gierke et al, 1981;Xue et al, 1989;Lee et al, 1992) observations. Readers are referred to review articles by Mauritz (1988) and Heitner-Wirguin (1996) for more information.…”

Section: Introductionmentioning

confidence: 82%

Micromechanical analysis of ionic clustering in Nafion perfluorinated membrane

Nemat‐Nasser

2000

Mechanics of Materials

105

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The cluster morphology in a water-swollen Na®on per¯uorinated membrane is studied using a micromechanics approach. The cluster size is determined from the minimization of the free energy as a function of the equivalent weight of Na®on, the volume fraction of water, and the temperature, taking into account the electrostatic dipole interaction energy, the elastic polymer chain reorganization energy, and the cluster surface energy, leading to results which are in accord with experimental observations. By minimizing the sum of: (1) the electro-elastic interaction energy between an ionic cluster and the¯uorocarbon matrix, and (2) the cluster surface energy, it is concluded that the eective cluster shape is spherical in the absence of an electric ®eld, and becoming an oblate spheroid when an electric ®eld is applied. The eect of cluster morphology on the eective electro-elastic moduli and the eective ionic conductivity is then studied by a micromechanical multi-inclusion model. The result seems to describe the available empirical relation when a spherical cluster shape is assumed. It correctly predicts the insulator-to-conductor transition which occurs in Na®on, as the water volume fraction is increased. Ó

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Section: Introductionmentioning

confidence: 82%

Micromechanical analysis of ionic clustering in Nafion perfluorinated membrane

Nemat‐Nasser

2000

Mechanics of Materials

105

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“…There are several approaches in order to explain the actuation mechanism of IPMC membrane [9][10][11][12][13][14][15]. Both the structure of the material and the transport mechanism of ion exchange membranes enable the actuation of IPMCs.…”

Section: Introductionmentioning

confidence: 99%

“Equivalent” Electromechanical Coefficient for IPMC Actuator Design Based on Equivalent Bimorph Beam Theory

Çilingir

Papila

2010

Exp Mech

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This paper addresses an "equivalent" electromechanical coupling coefficient that may be used in designing Ionic Polymer Metal Composite (IPMC) actuators. The coefficient is not a material constant and derived from equivalent bimorph beam model. The collective effect of the membrane thickness and operating voltage on the coefficient is demonstrated by using a design of experiment (DOE) of three and five levels of the two factors, respectively. Experiments and linear finite element analyses with MD.NASTRAN at DOE points are performed. The tip displacement and the coupling coefficient are reported and their response surface (RS) approximations as function of the thickness and voltage are constructed. Experiments and RS predictions indicate that actuator thickness and applied voltage are two interacting major factors for maximum tip displacement. The equivalent coupling coefficient is primarily driven by the thickness of actuator moreover voltage appears to contribute as the thickness increases. The initial curvature of the strips before electrical excitation is also shown to be a factor for "equivalent" coupling coefficient, it is not, however sufficient to explain the variation in the experimental data. A correction factor approach is proposed and applied to the straight beam tip displacement RS that filters out experimental variation. A corrected RS enables including the pre-imposed initial curvature as design parameter along with the actuator thickness and the operating peak voltage when predicting the tip displacement and the equivalent coupling coefficient.

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“…To investigate the structure and swelling behavior of the hydrated Nafion membranes, numerous experimental efforts have been concentrated on neutron, wide and small angle X-ray scattering, infrared (IR) and Raman spectroscopy, and transmission electron microscopy (TEM) techniques. [1][2][3][4][5][6][7][8][9][10][11][12][13] It has been well established that hydrated Nafion membranes have two phases on a nanometer scale, a hydrophobic phase containing the backbone and a hydrophilic phase containing sulfonic acid groups and water. Several models for these structures such as the interconnected spherical water clusters (the cluster-network model) have been proposed for the interpretation of the scattering patterns.…”

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confidence: 99%

A Computer Simulation Study of the Mesoscopic Structure of the Polyelectrolyte Membrane Nafion

Yamamoto

Hyodo

2003

Polym J

164

214

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ABSTRACT:We studied the mesoscopic structure of the perfluorinated sulfonic acid membrane Nafion containing water using a dissipative particle dynamics (DPD) simulation. A Nafion polymer is modeled by connecting coarsegrained particles, which correspond to the hydrophobic backbone of polytetrafluoroethylene and perfluorinated side chains terminated by hydrophilic end particles of sulfonic acid groups. Water is also modeled by the same size particle as adopted in the Nafion model, corresponding to a group of four H 2 O molecules. The Flory-Huggins χ-parameters between DPD particles are estimated from the mixing energy calculation using an atomistic simulation. In the DPD simulation, water particles and hydrophilic particles of Nafion side chains spontaneously form aggregates and are embedded in the hydrophobic phase of the Nafion backbone. This structure is a bicontinuous phase of Nafion and water regions and has a continuous path in the cavity of water in any direction. Although this sponge-like structure is essentially identical to the cluster-network model proposed from the experimental studies, the shape of the water clusters is not spherical but irregular, and the water regions are indistinguishable structures of water clusters and their channels. The cluster size and its dependence on the water content are in good agreement with experimental reports; therefore, the simulated mesoscopic structure is confirmed to be a highly possible one.KEY WORDS Computer Simulation / Dissipative Particle Dynamics / Polyelectrolyte Membrane / Mesoscopic Structure / Morphology / Nafion Membrane / Water Cluster / The well-known perfluorinated sulfonic acid membranes Nafion are the most common membrane materials used in the polymer electrolyte fuel cell because of their exceptional chemical, thermal and mechanical stability in addition to their reasonable proton conductivity. A Nafion polymer consists of a polytetrafluoroethylene backbone and perfluorinated pendant side chains terminated by sulfonic acid groups. The general molecular structure of Nafion polymer is 1where n is approximately 5-14, and m is 200-1000. To investigate the structure and swelling behavior of the hydrated Nafion membranes, numerous experimental efforts have been concentrated on neutron, wide and small angle X-ray scattering, infrared (IR) and Raman spectroscopy, and transmission electron microscopy (TEM) techniques. 1-13 It has been well established that hydrated Nafion membranes have two phases on a nanometer scale, a hydrophobic phase containing the backbone and a hydrophilic phase containing sulfonic acid groups and water. Several models for these structures such as the interconnected spherical water clusters (the cluster-network model) have been proposed for the interpretation of the scattering patterns. 1-7 However, these models are still under discussion concerning the size and shape of the water clusters. It is meaningful to clarify the structure of the membranes for analytical study and to improve the mechanical and transport properties of the m...

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Characterization of nafion® membranes by transmission electron microscopy

Cited by 97 publications

References 17 publications

Micromechanical analysis of ionic clustering in Nafion perfluorinated membrane

Micromechanical analysis of ionic clustering in Nafion perfluorinated membrane

“Equivalent” Electromechanical Coefficient for IPMC Actuator Design Based on Equivalent Bimorph Beam Theory

A Computer Simulation Study of the Mesoscopic Structure of the Polyelectrolyte Membrane Nafion

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