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Hydration of Polymer Membranes

The behavior of water in polymer membranes and films is important for many applications. In hydrogen fuel cells, the polymer membranes that conduct protons from the anode to the cathode require that the polymer be well hydrated. In polymer films used for packaging the ability to prevent the transport of water is important to ensure that the contents inside the packaging remain dry.

On this page, we provide a visualization of two polymers that can be hydrated as membranes or films. Nafion is a perfluorosulfonic acid polymer that has a hydrophobic teflon backbone and a hydrophilic side chain terminated with a sulfonic acid group. Nafion is used in fuel cells. Chitosan is a naturally occurring polymer that has amine groups that can be hydrated. However, the backbone of Chitosan is hydrophilic relative to Nafion. Therefore the distribution of water in these systems is very different.

On this page, the visualizations show only a single isolated Nafion chain and Chitosan chain, which clearly shows their structures. There is also a page in which all atoms in the hydrated membrane system are shown, although in this case it is difficult to see the distribution of water within the polymer. Therefore, there is also a page in which only the aqueous phase in the system are shown, which makes it easier to visualize the distribution of water within the polymer.

Interactive Structures

A single chain of Nafion (degree of polymerization = 8, equivalent weight = 1144).

A single chain of Chitosan. This chain is composed of 5 units of chitin and 10 units of chitosan. (C100H59N15O66). This particular polymer is AABAA+BAABAABAA+B where A = chitosan, A+ = acidified chitosan & B = chitin. The amine groups on 2 of the 10 units of chitosan are hydroxylated. (Anions not shown.)

Color Legend:

  • Red = Oxygen
  • White = Hydrogen
  • Yellow = Sulfur
  • Gray = Carbon
  • Blue = Nitrogen
  • Green = Fluorine


Nafion References:
Cui, S.T., Liu, J., Esai Selvan, M., Keffer, D.J., Edwards, B.J., Steele, W.V., "A Molecular Dynamics Study of a Nafion Polyelectrolyte Membrane and the Aqueous Phase Structure for Proton Transport", J. Phys. Chem. B 111(9) 2007 p. 2208-2218. doi: 10.1021/jp066388n.

Cui, S., Liu, J., Esai Selvan, M., Paddison, S.J., Keffer, D.J., Edwards, B.J., "Comparison of the Hydration and Diffusion of Protons in Perfluorosulfonic Acid Membranes with Molecular Dynamics Simulations", J. Phys. Chem. B 112(42) 2008 pp. 13273-13284. doi: 10.1021/jp8039803.

Liu, J., Suraweera, N., Keffer, D.J., Cui, S., Paddison, S.J., "On the Relationship Between Polymer Electrolyte Structure and Hydrated Morphology of Perfluorosulfonic Acid Membranes", J. Phys. Chem. C 114(25) 2010 pp 11279-11292. doi: 10.1021/jp911972e.

Esai Selvan, M., Calvo-Muñoz, E.M., Keffer, D.J., "Toward a Predictive Understanding of Water and Charge Transport in Proton Exchange Membranes", J. Phys. Chem. B 115(12) 2011 pp 3052-3061. doi: 10.1021/jp1115004.

Esai Selvan, M., Keffer, D.J., Cui, S., "A Reactive Molecular Dynamics Study of Proton Transport in Polymer Electrolyte Membrane", J. Phys. Chem. C 115(38) 2011 pp. 18835-18846. doi: 10.1021/jp203443c.

Chitosan References:
McDonnell, M.T., Greeley, D., Kit, K., Keffer, D.J., "Modeling Oxygen Permeability in Biodegradable Polymer Films", in preparation, 2014.

Similar structures are available for other polymer membranes including, xs-PCHD and xs-PCHD/PEG membranes:
Wang, Q., Suraweera, N.S., Keffer, D.J., Deng, S., Mays, J.W., "Atomistic and Coarse-Grained Molecular Dynamics Simulation of a Cross-Linked Sulfonated Poly (1,3-cyclohexadiene)-based Proton Exchange Membrane", Macromolecules, 45(16) 2012 pp 6669-6685. doi: 10.1021/ma300383z

Wang, Q., Keffer, D.J., Deng, S., Mays, J.W., "Structure and Diffusion in Cross-linked and Sulfonated Poly (1, 3-cyclohexadiene)/Polyethylene Glycol-based Proton Exchange Membranes", J. Phys. Chem. C 117(10) 2013 pp. 4901-4912. doi: 10.1021/jp309793z.

posted: July 2014.
updated: July 2014.