A new force field for molecular dynamics studies of Li+ and Na+-nafion

Endel Soolo; Anti Liivat; Heiki Kasemägi; Tarmo Tamm; Daniel Brandell; Alvo Aabloo

doi:10.1117/12.775963

10 April 2008 A new force field for molecular dynamics studies of Li⁺ and Na⁺-nafion

Endel Soolo, Anti Liivat, Heiki Kasemägi, Tarmo Tamm, Daniel Brandell, Alvo Aabloo

Proceedings Volume 6927, Electroactive Polymer Actuators and Devices (EAPAD) 2008; 69270E (2008) https://doi.org/10.1117/12.775963
Event: SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring, 2008, San Diego, California, United States

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.

Citation Download Citation

Endel Soolo, Anti Liivat, Heiki Kasemägi, Tarmo Tamm, Daniel Brandell, and Alvo Aabloo "A new force field for molecular dynamics studies of Li⁺ and Na⁺-nafion", Proc. SPIE 6927, Electroactive Polymer Actuators and Devices (EAPAD) 2008, 69270E (10 April 2008); https://doi.org/10.1117/12.775963

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