Article,
Nanophase segregation and water dynamics in hydrated Nafion: Molecular modeling and experimental validation
JOURNAL OF CHEMICAL PHYSICS, (2008)
DOI: 10.1063/1.3000641
Abstract
Reported results of coarse-grained molecular dynamics simulations
rationalize the effect of water on the phase-segregated morphology of
Nafion ionomers. We analyzed density maps and radial distribution
functions and correlated them with domain structures, distributions of
protogenic side chains, and water transport properties. The mesoscopic
structures exhibit spongelike morphologies. Hydrophilic domains of
water, protons, and anionic side chains form a random three-dimensional
network, which is embedded in a matrix of hydrophobic backbone
aggregates. Sizes of hydrophilic domains increase from 1 to 3 nm upon
water uptake. At low water content, hydrophilic domains are roughly
spherical and poorly connected. At higher water content, they convert
into elongated cylindrical shapes with high connectivity. Further
structural analysis provides a reasonable estimate of the percolation
threshold. Radial distribution functions from coarse-grained and
atomistic molecular dynamics models exhibit a good agreement. Water
cluster size distributions from coarse-grained molecular dynamics and
dissipative particle dynamics are consistent with small angle x-ray
scattering data. Moreover, we calculated the water diffusivity by
molecular dynamics methods and corroborated the results by comparison
with pulsed field gradient NMR.
Tags
- dynamics
- magnetic
- method;
- molecular
- nuclear
- phase
- polymers;
- resonance;
- scattering}
- separation;
- water;
- x-ray
- {aggregation;
