mz400322q_si_001.pdf (332.17 kB)
Multistep Thickening of Nafion Thin Films in Water
journal contribution
posted on 2016-02-18, 15:57 authored by Yudai Ogata, Daisuke Kawaguchi, Norifumi
L. Yamada, Keiji TanakaWater sorption kinetics in thin Nafion
films prepared on silver
and silicon oxide substrates was examined by surface plasmon resonance
and neutron reflectivity measurements. It was found that the films
thickened in three regimes. The asymptotic swelling ratios in regimes
I, II, and III were 1.05, 1.26, and 1.41, respectively. These values
were independent of the substrate species and were coincident with
the transition points of different hydration states in the bulk Nafion;
water binding to sulfonic acid groups, the formation of sphere-like
ionic clusters, and bridge formation between clusters. The swelling
was much slower in thin films than in the bulk due to the mobility
restriction of Nafion near the substrate.