Substrate‐Dependent Molecular and Nanostructural Orientation of Nafion Thin Films
Abstract
The effects of film thickness and substrate composition on the ionomer structure in porous electrodes are critical in understanding pathways toward developing higher performance electrochemical devices, including fuel cells and batteries. Insights are gained into the molecular and nanostructural orientation dependence for thin Nafion films (12–300 nm thick) on gold, platinum, and SiO2 model substrates. Molecular orientation is determined from the birefringence measured using spectroscopic ellipsometry, while the nanostructural orientation of the ionic domains is measured using grazing‐incidence small‐angle X‐ray scattering. Density functional theory calculations for the molecular polarizability of the Nafion backbone and side chain show complimentary contributions to the measured birefringence values for the material. Nafion films prepared on SiO2 substrates exhibit a nearly isotropic molecular and nanostructural orientation. Films on gold and platinum display parallel backbone orientations, relative to the substrate, with decreasing film thickness. However, a birefringence transition toward molecular isotropy is observed for 30 nm thick films on Au and Pt; while the ionic nanostructured domains continuously align parallel to the substrate. This apparent isotropic molecular orientation with increasing domain orientation highlights the difference between the backbone and side chain orientation, a key finding for elucidating transport in confined films at the interfaces.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Jul 11, 2019
- Source ID
- 10.1002/adfm.201902699
Entities
People
- Ahmet Kuşoğlu
- Douglas I Kushner
- Michael A. Hickner
- Nikolas J. Podraza
Organizations
- ALS Association
- Army Research Office
- Fuel Cell Technologies Office
- General Motors
- Institutes of Energy and the Environment, Pennsylvania State University
- Lawrence Berkeley National Laboratory
- Materials Research Institute, Pennsylvania State University
- Office of Energy Efficiency and Renewable Energy
- Office of Naval Research
- Office of Science
- Pennsylvania State University
- United States Department of Energy
- University of Toledo