Time-resolved total reflection detects mass transfer along thickness direction of bulk Nafion® film

Abstract

To elucidate a bulk membrane (Nafion®) with respect to channel connectivity or mass transfer (water or ions) through the channels, we propose to utilize time-resolved neutron reflectivity and deuterium exchange method. We performed the experiment on time-of-flight spectrometer iMATERIA at pulsed neutron spallation source J-PARC in Tokai, Japan. To exchange water (D2O or H2O) in the film during RF measurements, we specially designed a sample environment with Si substrates. A bulk film (50 μm thickness) is sandwiched by Si substrate (5 mm thickness) and Al mesh plate. The incident neutron incomes from edge of Si substrate and reflects at a front surface of bulk film. When we exchange water (D2O or H2O), water flows through Al mesh and starts to diffuse in the film. When exchanged water reaches to a front surface of the film, critical angle for total reflection (or critical wave number) changes, according to the chemical composition and therefore the averaged coherent scattering length (bav) at the front surface. Consequently, diffusion coefficient is determined from time-dependence in bav.