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Abstract

A recently derived molecular structure function model based on
non-equilibrium statistical mechanics has been used to compute
proton friction and diffusion coefficients in 65% sulfonated
PEEKK membranes at various degrees of hydration. Morphological
parameters, taken from recent SAXS measurements, including pore
radius and average separation distance of the sulfonate fixed
sites within the pore, along with results from electronic
structure explicit water calculations for para-toluene sulfonic
acid, were used as input parameters in the model. For membranes
where the hydration levels (lambda) were 15, 23, and 30
H2O's/SO3(-), the model predicted proton diffusion coefficients
of 4.13 x 10(-10), 1.23 x 10(-9), and 1.54 x 10(-9) m(-2) s(-
1), respectively. These values were obtained without any
attempt at fitting to the results obtained from pulsed-field
gradient NMR experiments. These computed diffusion coefficients
are all within approximately 15% of the measured values;
demonstrating the substantial predictive capability of the
model. Furthermore, this investigation has shown that at the
lower water content (lambda = 15) the transport of the proton
may be adequately described as vehicular in nature, while at
the two higher water contents (lambda = 23, 30) there is a
contribution via structural diffusion.