Scaling Behavior of Nafion with Different Model Parameterizations in Dissipative Particle Dynamics Simulations

The scaling behavior of the conformation and dynamics of mesoscopic models of a polymer melt, Nafion, and hydrated Nafion are investigated with dissipative particle dynamics (DPD) simulations. The scaling behavior of all studied systems generally follows the Rouse theory. For the polymer melt and dry Nafion, increase in chain stiffness slightly shrinks the polymer and leads to slower dynamics with longer polymer relaxation time. The addition of a stiff constraint to five different DPD parameterizations of hydrated Nafion expands the chain conformation, while the repulsion parameter effect on size is secondary. In contrast, softer repulsion predominately dictates faster dynamics of both the polymer and water, and stiffer chains also lead to improved water diffusion to a much lesser extent. Sufficiently long Nafion chains are required to realistically represent the relatively immobile Nafion framework and mobile proton conducting water domain. Direct quantitative cluster size analysis is advocated to characterize the water channel connectivity.