Characteristics of Self-Assembled Ultrathin Nafion Films

Self-assembled Nafion films of varying thickness were generated on SiO2 terminated silicon wafer by immersion in Nafion dispersions of different concentrations. The impact of solvent/dispersion media was probed by preparing films from two different types of Nafion dispersions—IPA-diluted dispersion and Nafion-in-water dispersion. The thickness of films was ascertained by three different techniques: variable angle spectroscopic ellipsometry (VASE), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The three techniques yielded consistent nominal thicknesses of 4, 10, 30, 55, 75, 110, 160, and 300 nm for films self-assembled from IPA-diluted Nafion dispersions of concentrations 0.1, 0.25, 0.5, 1.0, 1.5, 2.0, 3.0, and 5.0 wt %, respectively. Films generated from 0.25–5.0 wt % Nafion-in-water dispersions generated comparable thicknesses. An interesting finding of our work is the observation of bimodal surface wettability, investigated by water contact angle. The sub-55 nm films were fo...