Description Based on CGMD

Both CGMD and DPD simulations indicate a percolation threshold for hydrophilic domains at A 4, which corresponds to a 10% volume fraction of water. The low value of the conductivity percolation threshold in Nation PEMs has been concluded as well from proton conductivity studies (Cappadonia et al., 1994, 1995). The high interconnectivity of water channels and the peculiarities of swelling and reorganization of the polymer matrix upon water uptake promote percolation at low water content (Eikerling et al., 1997, 2008). 

Other MD simulations predicted markedly larger values of the percolation threshold (Devanathan et al., 2007b Elliott and Paddison, 2007). Discrepancies in calculated percolation thresholds could be artifacts of overly simplistic representations of ionomer chains in molecular-level simulations. Atomistic models fail in reproducing sizes and shapes of water clusters and polymer aggregates as well as in predicting percolation thresholds, swelling behavior, and related transport properties, if the monomeric sequences that they employ are too short. Notably, for the same reason, many simulations would be inept to reproduce the persistence length of the base ionomer. 

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