Evaluation of the Single Pore Model

The reference set of parameters was provided in Eikerling and Berg (2011). In the case of material-specific parameters, Nafion is the benchmark system. The pore walls should be considered as hydrophilic. Hence, 0 = 0 is a reasonable choice. For the mean value of the wall charge density, a value ao = —0.08 C m was taken at the fixed reference radius of 7 o = 1 nm. This value depends on the lEC and the structure of ionomer bundles. 

Elastic properties of Nafion-type PEMs have been discussed in Silberstein (2008) and Jalani and Datta (2005). Data are available only for macroscopic effective elastic moduli. These properties vary significantly with T and RH, ionomer chemistry, and membrane preconditioning. In the model, information is required for the elastic modulus of microscopic polymer fibrils or walls. These values should be significantly larger than macroscopic values, persumably lying in the range of G = 200 to 400 MPa. 

In the following study of pore filling and swelling, it is assumed that each pore is characterized by one value of ao. The value of ao is used in Equations 2.43 and 2.44 under VE or Equations 2.45 and 2.46 under LE conditions to find the swelling 

porosimetry, and water sorption studies provide ample evidence for the dispersion in pore size and the evolution of the pore size distribution in the PEM upon water uptake. The changes in the pore space morphology upon water uptake translate into variations in transport properties of the PEM, as is well known (Eikerling et al., 1997, 2007a, 2008 Kreuer et al., 2004). There is, however, uncertainty regarding the mechanism of these macroscopic swelling phenomena. 

This section will focus on ensemble effects and pore network reorganization upon water uptake. It will be demonstrated how these structural changes are related to 

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