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Nanophase-Segregation and Transport in Nafion 117 from Molecular Dynamics Simulations: Effect of Monomeric Sequence

Jang, Seung Soon and Molinero, Valeria and Çağin, Tahir and Goddard, William A., III (2004) Nanophase-Segregation and Transport in Nafion 117 from Molecular Dynamics Simulations: Effect of Monomeric Sequence. Journal of Physical Chemistry B, 108 (10). pp. 3149-3157. ISSN 1520-6106. http://resolver.caltech.edu/CaltechAUTHORS:20170524-113944247

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Abstract

Nafion polyelectrolyte is widely used in polymer electrolyte membrane fuel cells (PEMFC) due to its high proton conductivity. The properties of hydrated Nafion are attributed to its nanophase-segregated structure in which hydrophilic clusters are embedded in a hydrophobic matrix. However, there has been little characterization of how the monomeric sequence of the Nafion chain affects the nanophase-segregation structure and transport in hydrated Nafion. To study such properties, we carried out molecular dynamics (MD) simulations of Nafion 117 using two extreme monomeric sequences:  one very blocky and other very dispersed. Both produce a nanophase-segregated structure with hydrophilic and hydrophobic domains. However, the blocky Nafion leads to a characteristic dimension of phase-segregation that is ∼60% larger than for the dispersed system. We find that the water−polymer interface is heterogeneous, consisting of hydrophilic patches (water contacting sulfonate groups of Nafion) and hydrophobic patches (water contacting fluorocarbon group). The distribution of the hydrophilic and the hydrophobic patches at the interface (i.e., the heterogeneity of interface) is much more segregated for blocky Nafion. This leads to a water diffusion coefficient for the dispersed case that is ∼25% smaller than for the blocky case (0.46 × 10^(-5) vs 0.59 × 10^(-5) cm^2/s at 300 K). The experimental value (0.50 × 10^(-5) cm^2/s) is within the calculated range. On the other hand, we find that the vehicular diffusion of hydronium is not affected significantly by the monomeric sequence. These results should be useful in optimizing the properties of Nafion and as targets for developing other membranes to replace Nafion in PEMFC and other applications.


Item Type:Article
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URLURL TypeDescription
http://dx.doi.org/10.1021/jp036842cDOIArticle
http://pubs.acs.org/doi/abs/10.1021/jp036842cPublisherArticle
ORCID:
AuthorORCID
Çağin, Tahir0000-0002-3665-0932
Goddard, William A., III0000-0003-0097-5716
Additional Information:© 2004 American Chemical Society. Received 23 September 2003. Published online 17 February 2004. Published in print 1 March 2004. This research was supported in part by General Motors (GAPC, Dr. G. Voecks). The facilities of the Materials and Process Simulation Center used for these studies are supported by DURIP-ARO, DURIP-ONR, IBM-SUR, and NSF (MRI) and other support for the MSC comes from MURI-ARO, MURI-ONR, DOE, ONR, NSF-CSEM, NIH, General Motors, ChevronTexaco, Seiko-Epson, Beckman Institute, and Asahi Kasei.
Funders:
Funding AgencyGrant Number
General MotorsUNSPECIFIED
Army Research Office (ARO)UNSPECIFIED
Office of Naval Research (ONR)UNSPECIFIED
IBMUNSPECIFIED
NSFUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
NIHUNSPECIFIED
ChevronTexacoUNSPECIFIED
Seiko-EpsonUNSPECIFIED
Caltech Beckman InstituteUNSPECIFIED
Asahi KaseiUNSPECIFIED
Record Number:CaltechAUTHORS:20170524-113944247
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20170524-113944247
Official Citation:Nanophase-Segregation and Transport in Nafion 117 from Molecular Dynamics Simulations:  Effect of Monomeric Sequence Seung Soon Jang,Valeria Molinero,Tahir Çaǧın, and William A. Goddard III The Journal of Physical Chemistry B 2004 108 (10), 3149-3157 DOI: 10.1021/jp036842c
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77713
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:24 May 2017 19:49
Last Modified:24 May 2017 19:49

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