Electrokinetic measurements of thin Nafion films.

We perform an electrokinetic characterization of ~300 nm Nafion films deposited on glass slides over a relatively unexplored region of ionic strength and pH. Owing to the small pore size of the Nafion, we probe the Nafion-fluid interface with the streaming potential measurement, and we probe ionic transport through the entire thickness of the Nafion film with the conductivity measurements. By applying a transport model for each of these measurements, we show that the inferred fixed charge density and characteristic fluid resistance length is different in each case. Analyzing our results with data from the literature, we suggest that our result is consistent with a thin Nafion film that is both nonuniform and weakly hydrated. Our regimen of experimentation and analysis may be generalized to characterize other porous and charged layers.