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A molecular dynamics study of the effect of side-chains on mobility in a polymer host
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Materials Chemistry. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Materials Chemistry, Structural Chemistry. strukturkemi.
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Materials Chemistry. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Materials Chemistry, Structural Chemistry. strukturkemi.
2005 (English)In: Solid State Ionics, Vol. 176, no 39-40, 3041-3044 p.Article in journal (Refereed) Published
Abstract [en]

The effect on polymer dynamics of adding methoxy-terminated poly(ethylene oxide) (PEO) side-chains with different lengths and separations to an amorphous long-chain PEO backbone has been studied by Molecular Dynamics (MD) simulation at 293 K and 330 K. The study is seen as having a direct general relevance to the optimal design of ion-conducting polymer hosts for both Li-ion battery and polymer fuel-cell applications. The MD box used contains a long-chain PEO backbone to which side-chains comprising 3, 6, 7, 8, 9 and 15 EO units are added. The chosen separations between the side-chains are 5, 10, 15, 20 and 50 EO units. All potentials used to describe these systems are taken from earlier work (J. Mater. Chem., 13 (2003) 214). The overall mobility of the polymer host system is found to have both minima and maxima at both temperatures for side-chain lengths in the range 6–9 EO units. This is almost totally independent of side-chain separation at 293 K, while the situation is more complex at 330 K.

Place, publisher, year, edition, pages
2005. Vol. 176, no 39-40, 3041-3044 p.
Keyword [en]
Molecular dynamics, Polymer side-chains, Chain separation, Ion conduction, Mobility, Polymer fuel cells
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-75441DOI: doi:10.1016/j.ssi.2005.10.003OAI: oai:DiVA.org:uu-75441DiVA: diva2:103352
Available from: 2006-02-07 Created: 2006-02-07 Last updated: 2011-01-11
In thesis
1. The Rôle of Side-Chains in Polymer Electrolytes for Batteries and Fuel Cells
Open this publication in new window or tab >>The Rôle of Side-Chains in Polymer Electrolytes for Batteries and Fuel Cells
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The subject of this thesis relates to the design of new polymer electrolytes for battery and fuel cell applications. Classical Molecular Dynamics (MD) modelling studies are reported of the nano-structure and the local structure and dynamics for two types of polymer electrolyte host: poly(ethylene oxide) (PEO) for lithium batteries and perfluorosulfonic acid (PFSA) for polymer-based fuel cells. Both polymers have been modified by side-chain substitution, and the effect of this on charge-carrier transport has been investigated. The PEO system contains a 89-343 EO-unit backbone with 3-15 EO-unit side-chains, separated by 5-50 EO backbone units, for LiPF6 salt concentrations corresponding to Li:EO ratios of 1:10 and 1:30; the PFSA systems correspond to commercial Nafion®, Hyflon® (Dow®) and Aciplex® fuel-cell membranes, where the major differences again lie in the side-chain lengths.

The PEO mobility is clearly enhanced by the introduction of side-chains, but is decreased on insertion of Li salts; mobilities differ by a factor of 2-3. At the higher Li concentration, many short side-chains (3-5 EO-units) give the highest ion mobility, while the mobility was greatest for side-chain lengths of 7-9 EO units at the lower concentration. A picture emerges of optimal Li+-ion mobility correlating with an optimal number of Li+ ions in the vicinity of mobile polymer segments, yet not involved in significant cross-linkages within the polymer host.

Mobility in the PFSA-systems is promoted by higher water content. The influence of different side-chain lengths on local structure was minor, with Hyflon® displaying a somewhat lower degree of phase separation than Nafion®. Furthermore, the velocities of the water molecules and hydronium ions increase steadily from the polymer backbone/water interface towards the centre of the proton-conducting water channels. Because of its shorter side-chain length, the number of hydronium ions in the water channels is ~50% higher in Hyflon® than in Nafion® beyond the sulphonate end-groups; their hydronium-ion velocities are also ~10% higher.

MD simulation has thus been shown to be a valuable tool to achieve better understanding of how to promote charge-carrier transport in polymer electrolyte hosts. Side-chains are shown to play a fundamental rôle in promoting local dynamics and influencing the nano-structure of these materials.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 52 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 635
Keyword
molecular dynamics, polymer electrolytes, side-chains, Li-ion batteries, proton exchange membrane fuel cell (PEMFC), PFSA membrane
National Category
Other Chemistry Topics Atom and Molecular Physics and Optics
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-100738 (URN)978-91-554-7499-7 (ISBN)
Public defence
2009-05-11, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2009-04-20 Created: 2009-04-06 Last updated: 2012-10-09

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Karo, JaanusThomas, John Oswald

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