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Proceedings Paper

A new force field for molecular dynamics studies of Li+ and Na+-nafion
Author(s): Endel Soolo; Anti Liivat; Heiki Kasemägi; Tarmo Tamm; Daniel Brandell; Alvo Aabloo
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Paper Abstract

Nafion is widely known as one of the most popular membrane materials for low temperature fuel cell applications. However, the particular exchange membrane material properties make it also valuable for other applications. One of the electroactive polymer (EAP) subclasses, ionic polymer metal composites (IPMC) commonly exploits Nafion as the ion exchange polymer membrane. The ion conducting properties of Nafion are extremely important for IPMCs. Although, ion conductivity depends strongly on the structural properties of the polymer matrix, there has been very little insight at the atomistic level. Molecular dynamics simulations are one of the possibilities to study the ion conduction mechanism at atomistic level. So far, the simulation results have been rather contradictory and very much dependent from the force fields and polymer matrix setup used. In the present work, new force field parameters for Li+ and Na+ - nafion based on DFT calculations are presented. The developed potentials and the force field were tested by molecular dynamics simulations. It can be concluded that Li+ and Na+ ions are coordinated to different Nafion side-chain terminal group (SO3-) oxygens and to very few water molecules. One cation is coordinated to three different side-chains. Oxygens of SO3 groups and cations form complicated multi-header systems. In the equilibrium state, no cations dissociated from side chains were found.

Paper Details

Date Published: 10 April 2008
PDF: 9 pages
Proc. SPIE 6927, Electroactive Polymer Actuators and Devices (EAPAD) 2008, 69270E (10 April 2008); doi: 10.1117/12.775963
Show Author Affiliations
Endel Soolo, Univ. of Tartu (Estonia)
Anti Liivat, Univ. of Tartu (Estonia)
Heiki Kasemägi, Univ. of Tartu (Estonia)
Tarmo Tamm, Univ. of Tartu (Estonia)
Daniel Brandell, Virginia Polytechnic Institute and State Univ. (United States)
Alvo Aabloo, Univ. of Tartu (Estonia)

Published in SPIE Proceedings Vol. 6927:
Electroactive Polymer Actuators and Devices (EAPAD) 2008
Yoseph Bar-Cohen, Editor(s)

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