Unraveling Depth-Specific Ionic Conduction and Stiffness Behavior across Ionomer Thin Films and Bulk Membranes

Seefat Farzin, Ehsan Zamani, Shudipto K. Dishari

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


Interfacial behavior of submicron thick polymer films critically controls the performance of electrochemical devices. We developed a robust, everyday-accessible, fluorescence confocal laser scanning microscopy (CLSM)-based strategy that can probe the distribution of mobility, ion conduction, and other properties across ionomer samples. When fluorescent photoacid probe 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) was incorporated into <1 μm thick Nafion films on substrates, the depth-profile images showed thickness- and interface-dependent proton conduction behavior. In these films, proton conduction was weak over a region next to substrate interface, then gradually increased until air interface at 88% RH. Conversely, consistently high proton conduction with no interface dependence was observed across 35-50 μm thick bulk, free-standing Nafion membranes. A hump-like mobility/stiffness distribution was observed across Nafion films containing mobility-sensitive probe (9-(2-carboxy-2-cyanovinyl)julolidine) (CCVJ). The proton conduction and mobility distribution were rationalized as a combinatorial effect of interfacial interaction, ionomer chain orientation, chain density, and ionic domain characteristics.

Original languageEnglish (US)
Pages (from-to)791-798
Number of pages8
JournalACS Macro Letters
Issue number7
StatePublished - Jul 20 2021

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry


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