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Abstract Organic mixed conductors are increasingly employed in electrochemical devices operating in aqueous solutions that leverage simultaneous transport of ions and electrons. Indeed, their mode of operation relies on changing their doping (oxidation) state by the migration of ions to compensate for electronic charges. Nevertheless, the structural and morphological changes that organic mixed conductors experience when ions and water penetrate the material are not fully understood. Through a combination of electrochemical, gravimetric, and structural characterization, the effects of water and anions with a hydrophilic conjugated polymer are elucidated. Using a series of sodium‐ion aqueous salts of varying anion size, hydration shells, and acidity, the links between the nature of the anion and the transport and structural properties of the polymer are systematically studied. Upon doping, ions intercalate in the crystallites, permanently modifying the lattice spacings, and residual water swells the film. The polymer, however, maintains electrochemical reversibility. The performance of electrochemical transistors reveals that doping with larger, less hydrated, anions increases their transconductance but decreases switching speed. This study highlights the complexity of electrolyte‐mixed conductor interactions and advances materials design, emphasizing the coupled role of polymer and electrolyte (solvent and ion) in device performance.
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Ion effects on minimally hydrated polymers: hydrogen bond populations and dynamics
Compared to bulk water, the effect of ions in confined environments or heterogeneous aqueous solutions is less understood. In this study, we characterize the influence of ions on hydrogen bond populations and dynamics within minimally hydrated polyethylene glycol diacrylate (PEGDA) solutions using Fourier-transform infrared (FTIR) and two-dimensional infrared (2D IR) spectroscopies. We demonstrate that hydrogen bond populations and lifetimes are directly related to ion size and hydration levels within the polymer matrix. Specifically, larger monovalent cation sizes (Li+, Na+, K+) as well as anion sizes (F−, Cl−, Br−) increase hydrogen bond populations and accelerate hydrogen bond dynamics, with anions having more pronounced effects compared to cations. These effects can be attributed to the complex interplay between ion hydration shells and the polymer matrix, where larger ions with diffuse charge distributions are less efficiently solvated, leading to a more pronounced disruption of the local hydrogen bonding network. Additionally, increased overall water content results in a significant slowdown of dynamics. Increased water content enhances the hydrogen bonding network, yet simultaneously provides greater ionic mobility, resulting in a delicate balance between stabilization and dynamic restructuring of hydrogen bonds. These results contribute to the understanding of ion-specific effects in complex partially-hydrated polymer systems, highlighting the complex interplay between ion concentration, water structuring, and polymer hydration state. The study provides a framework for designing polymer membrane compositions with ion-specific properties.
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- Award ID(s):
- 1847199
- PAR ID:
- 10612341
- Publisher / Repository:
- Royal Society of Chemistry
- Date Published:
- Journal Name:
- Soft Matter
- Volume:
- 20
- Issue:
- 41
- ISSN:
- 1744-683X
- Page Range / eLocation ID:
- 8291 to 8302
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D4SM00830H
