Ion–polymer affinities of PEDOT:PSS from open-circuit titrations in a multi-cation background
6 affiliations
- 1Department of Biomedical, Metabolic and Neural Sciences
- 2University of Modena and Reggio Emilia
- 3Department of Materials Science and Engineering
- 4Stanford University
- 5Bio-inspired MEMS and Biomedical Devices, Engineering and Technology Institute Groningen (ENTEG)
- 6University of Groningen
Abstract
Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a widely used solid contact in solid-state ion-selective electrodes. In an electrolyte, the fixed charge of the PSS − backbone can exchange cations in a manner that depends on the electrolyte composition. Whether the sulfonate group has an intrinsic affinity for particular cations remains open. We estimate the fixed PSS charge density (c f = 1.18 M) from an open-circuit potential (OCP) calibration in pure NaCl, then independently dose NaCl, KCl, CaCl2 and MgCl2 into a 0.1× HEPES-buffered saline baseline containing the four cations at extracellular proportions and record the OCP of a PEDOT:PSS film after each addition. By inverting the titrations through a Donnan partition model, we numerically calculate the ion–polymer affinities k i . Taking Na + as reference, we find k K = 1.05, k Ca = 0.65 and k Mg = 0.44: the polyelectrolyte phase shows no measurable preference between monovalent cations Na + and K + , while showing less affinity with the divalent cations Ca 2+ and Mg 2+ . However, the divalent uptake remains substantial, since the affinity enters the partition linearly while the valence of the ion sits in the exponential of the Donnan potential. Therefore, the ionic composition of the film depends strongly on the ionic strength: at the used baseline Ca 2+ and Mg 2+ together compensate about half of the fixed charge while carrying under 5% of the cation charge in the electrolyte, a phenomenon known as electroselectivity. At 10× our baseline (physiological ionic strength) Na + dominates the PSS compensation and the divalent compensating fraction amounts to 10%.
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BibTeX
@misc{mele2026ionpolymer,
title = {{Ion–polymer affinities of PEDOT:PSS from open-circuit titrations in a multi-cation background}},
author = {Leandro Julian Mele and Gerwin Dijk and Alberto Salleo},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15008186/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008186/v1},
note = {CC BY-NC-ND},
}
RIS
TY - UNPB
TI - Ion–polymer affinities of PEDOT:PSS from open-circuit titrations in a multi-cation background
AU - Leandro Julian Mele
AU - Gerwin Dijk
AU - Alberto Salleo
PY - 2026
DA - 2026/09/01
PB - ChemRxiv
DO - 10.26434/chemrxiv.15008186/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008186/v1
AB - Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a widely used solid contact in solid-state ion-selective electrodes. In an electrolyte, the fixed charge of the PSS − backbone can exchange cations in a manner that depends on the electrolyte composition. Whether the sulfonate group has an intrinsic affinity for particular cations remains open. We estimate the fixed PSS charge density (c f = 1.18 M) from an open-circuit potential (OCP) calibration in pure NaCl, then independently dose NaCl, KCl, CaCl2 and MgCl2 into a 0.1× HEPES-buffered saline baseline containing the four cations at extracellular proportions and record the OCP of a PEDOT:PSS film after each addition. By inverting the titrations through a Donnan partition model, we numerically calculate the ion–polymer affinities k i . Taking Na + as reference, we find k K = 1.05, k Ca = 0.65 and k Mg = 0.44: the polyelectrolyte phase shows no measurable preference between monovalent cations Na + and K + , while showing less affinity with the divalent cations Ca 2+ and Mg 2+ . However, the divalent uptake remains substantial, since the affinity enters the partition linearly while the valence of the ion sits in the exponential of the Donnan potential. Therefore, the ionic composition of the film depends strongly on the ionic strength: at the used baseline Ca 2+ and Mg 2+ together compensate about half of the fixed charge while carrying under 5% of the cation charge in the electrolyte, a phenomenon known as electroselectivity. At 10× our baseline (physiological ionic strength) Na + dominates the PSS compensation and the divalent compensating fraction amounts to 10%.
ER -