Three-Dimensional Fine Structure of Nanometer-Scale Nafion Thin Films

Abstract

Nafion is a widely used polymer membrane in various applications ranging from advanced energy solutions to sensing of biomolecules. Despite the intensive research carried out over the years to reveal and understand the fine structure of Nafion, its structural features, especially as nanometer-scale films, are not unambiguously known. In this paper, we use room temperature scanning transmission electron microscopy (STEM) tomography complemented by glancing incidence small-angle X-ray scattering (GISAXS) and TEM at low temperatures to reveal the fine structure of thin (10−100 nm) unannealed Nafion films. The results from the detailed three-dimensional reconstructions obtained show that (i) the phase fractions of the hydrophobic and hydrophilic parts of the polymer are somewhat thickness-dependent, changing from 0.65/0.35 to about 0.7/0.3 when moving from 100 to 10 nm thick films; (ii) the channel diameters show a range of values from 3 to 6 nm in all the films independent of their thickness; (iii) the average distances between the hydrophilic channels inside the film have distributions centered around 12 nm (in 10 nm films), 15 nm (in 30 nm films), and 7 nm (in 100 nm films); (iv) in the thickest films, the hydrophilic channels exhibit higher interconnectivity and some of the channels appear to end within the Nafion film instead of going through the films; and (v) there are some confinement effects caused by the hydrophilic SiO 2 surface in the case of 10 and 30 nm thick films shown by the tendency of the hydrophilic channels to move horizontally near the substrate. Furthermore, a stable room temperature STEM tomography imaging method for Nafion films and a sample preparation method that preserves the characteristics of the hydrated morphology of Nafion in the dry state are demonstrated. These results provide a deeper understanding of the fine structure of Nafion thin films and provide a better means to characterize and understand their properties in different applications.

Electrochemical Detection of Morphine in Untreated Human Capillary Whole Blood

“…In a recent study on the detailed structure of Nafion thin films, the diameter of the nanoscale channels extending throughout the film were found to be between 3–6 nm . On the other hand, the dimensions of the most abundant protein in human blood, albumin, are about 3.8 nm in diameter and 15 nm in length .…”

“…41 In a recent study on the detailed structure of Nafion thin films, the diameter of the nanoscale channels extending throughout the film were found to be between 3−6 nm. 42 On the other hand, the dimensions of the most abundant protein in human blood, albumin, are about 3.8 nm in diameter and 15 nm in length. 43 Thus, it is conceivable that most proteinsas well as any opioid molecules bound to themare excluded from the Nafion-coated electrode surface, protecting the surface from biofouling.…”

Predicted Impacts of Pt and Ionomer Distributions on Low-Pt-Loaded PEMFC Performance

“…Previous thin-film Nafion experiments provide in situ measurements of total water uptake [21][22][23][24] and nano-structures. [23][24][25][26] However, dynamic in operando measurements that provide proton conductivity and/or oxygen diffusion are sparse or entirely lacking from literature. While the studies that do provide these transport parameters are helpful, 27,28 the thicknesses and substrates used are not always relevant to operating PEMFC CLs.…”

Dispersing Agents Impact Performance of Protonated Phosphonic Acid High-Temperature Polymer Electrolyte Membrane Fuel Cells

“…The average domain size of the hydrophilic regions is 4 nm, in good agreement with other reports. 20,21 No phase separation was observed for PWN from the high-magnification images.…”

“…High-magnification images (scale bar = 20 nm) show that the Nafion thin film has phase separation. The average domain size of the hydrophilic regions is 4 nm, in good agreement with other reports. , No phase separation was observed for PWN from the high-magnification images.…”