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Bridging length scales in organic mixed ionic–electronic conductors through internal strain and mesoscale dynamics


Understanding the structural and dynamic properties of disordered systems at the mesoscale is crucial. This is particularly important in organic mixed ionic–electronic conductors (OMIECs), which undergo significant and complex structural changes when operated in an electrolyte. In this study, we investigate the mesoscale strain, reversibility and dynamics of a model OMIEC material under external electrochemical potential using operando X-ray photon correlation spectroscopy. Our results reveal that strain and structural hysteresis depend on the sample’s cycling history, establishing a comprehensive kinetic sequence bridging the macroscopic and microscopic behaviours of OMIECs. Furthermore, we uncover the equilibrium and non-equilibrium dynamics of charge carriers and material-doping states, highlighting the unexpected coupling between charge carrier dynamics and mesoscale order. These findings advance our understanding of the structure–dynamics–function relationships in OMIECs, opening pathways for designing and engineering materials with improved performance and functionality in non-equilibrium states during device operation.

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Fig. 1: Operando GIXPCS to monitor chemical-potential-induced strain in adiabatic and non-adiabatic processes.
Fig. 2: Sequence of strain, phase contrast and charge kinetics.
Fig. 3: Mesoscale state reversibility in adiabatic and non-adiabatic processes.
Fig. 4: Mesoscale-domain self-dynamics.
Fig. 5: Domain coarsening of the Langevin Model B system and an associated schematic of the polymer morphology undergoing this process.

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Data availability

The original data underlying the figures in the main text are publicly available from the Northwestern University repository (Dryad) at The datasets generated and/or analysed during this current study are available from the corresponding authors upon request. Source data are provided with this paper.

Code availability

Both Python and MATLAB codes are publicly available via the Northwestern University repository (Dryad) at


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J.R. gratefully acknowledges funding support from the Alfred P. Sloan Foundation (award no. FG-2019-12046). R.W., B.D.P. and J.R. acknowledge support from the National Science Foundation (grant no. NSF DMR-1751308). This work is also funded by Northwestern’s MRSEC program (NSF DMR-2308691). This work utilized the SPID facility of Northwestern University’s NUANCE Center, which is partially supported by the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205), the Materials Research Science and Engineering Center (NSF DMR-2308691), the State of Illinois and Northwestern University. This research used resources of the Advanced Photon Source operated by the Argonne National Laboratory supported by the US Department of Energy (DOE), Office of Science (contract no. DE-AC02-06CH11357). Use of the Stanford Synchrotron Radiation Lightsource at SLAC National Accelerator Laboratory is supported by the US DOE, Office of Science, Office of Basic Energy Sciences (contract no. DE-AC02-76SF00515). We extend our special thanks to G. S. Shekhawat, H. Choi and L. J. Lauhon (Northwestern) for the attempt of in situ atomic force microscopy and related discussions. J.S. and Q.Z. acknowledge expert technical assistance of R. Ziegler (Argonne) and thank E. Dufrense (Argonne) and M. Sutton (Mcgill) for insightful and fruitful discussion.

Author information

Authors and Affiliations



R.W., D.M. and C.J.T. designed and tested the operando cell and conducted the experiments. J.S., S.N. and Q.Z. supported the operando GIXPCS measurements at the Advanced Photon Source. C.J.T., J.R. and B.D.P. conceived and directed the study. R.W. analysed the data and conducted the model simulation under the supervision of C.J.T. R.W., J.R. and C.J.T. wrote the manuscript with discussion and input from all authors.

Corresponding authors

Correspondence to Jonathan Rivnay or Christopher J. Takacs.

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Supplementary information

Supplementary Information

Supplementary Notes 1–5, Figs. 1–25 and Table 1.

Supplementary Video 1

Example XPCS patterns before strain alignment.

Supplementary Video 2

Example XPCS patterns after the first strain alignment.

Supplementary Video 3

Example XPCS patterns aligned after two iterations.

Supplementary Video 4

Example XPCS patterns aligned after 40 iterations.

Source data

Source Data Fig. 1

Operando GIXPCS to monitor chemical-potential-induced strain and scattering intensity in adiabatic and non-adiabatic processes.

Source Data Fig. 2

Sequence of strain, phase contrast and charge kinetics.

Source Data Fig. 4

Mesoscale-domain self-dynamics.

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Wu, R., Meli, D., Strzalka, J. et al. Bridging length scales in organic mixed ionic–electronic conductors through internal strain and mesoscale dynamics. Nat. Mater. 23, 648–655 (2024).

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