A microscopic origin for the breakdown of the Stokes Einstein relation in ion transport
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arXiv
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| Main Authors: | , , , , , , , , , , , |
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| Format: | Preprint |
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2026
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| _version_ | 1866912820152500224 |
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| author | Wei, Zhenyu Chen, Mu Ren, Jun He, Pinyao Xu, Wei Liu, Wei Zheng, Fei Zhang, Yin Si, Wei Sha, Jinjie Ni, Zhonghua Chen, Yunfei |
| author_facet | Wei, Zhenyu Chen, Mu Ren, Jun He, Pinyao Xu, Wei Liu, Wei Zheng, Fei Zhang, Yin Si, Wei Sha, Jinjie Ni, Zhonghua Chen, Yunfei |
| contents | Ion transport underlies the operation of biological ion channels and governs the performance of electrochemical energy-storage devices. A long-standing anomaly is that smaller alkali metal ions, such as Li$^+$, migrate more slowly in water than larger ions, in apparent violation of the Stokes-Einstein relation. This breakdown is conventionally attributed to dielectric friction, a collective drag force arising from electrostatic interactions between a drifting ion and its surrounding solvent. Here, combining nanopore transport measurements over electric fields spanning several orders of magnitude with molecular dynamics simulations, we show that the time-averaged electrostatic force on a migrating ion is not a drag force but a net driving force. By contrasting charged ions with neutral particles, we reveal that ionic charge introduces additional Lorentzian peaks in the frequency-dependent friction coefficient. These peaks originate predominantly from short-range Lennard-Jones (LJ) interactions within the first hydration layer and represent additional channels for energy dissipation, strongest for Li$^+$ and progressively weaker for Na$^+$ and K$^+$. Our results demonstrate that electrostatic interactions primarily act to tighten the local hydration structure, thereby amplifying short-range LJ interactions rather than directly opposing ion motion. This microscopic mechanism provides a unified physical explanation for the breakdown of the Stokes-Einstein relation in aqueous ion transport. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2601_08309 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | A microscopic origin for the breakdown of the Stokes Einstein relation in ion transport Wei, Zhenyu Chen, Mu Ren, Jun He, Pinyao Xu, Wei Liu, Wei Zheng, Fei Zhang, Yin Si, Wei Sha, Jinjie Ni, Zhonghua Chen, Yunfei Soft Condensed Matter Chemical Physics Ion transport underlies the operation of biological ion channels and governs the performance of electrochemical energy-storage devices. A long-standing anomaly is that smaller alkali metal ions, such as Li$^+$, migrate more slowly in water than larger ions, in apparent violation of the Stokes-Einstein relation. This breakdown is conventionally attributed to dielectric friction, a collective drag force arising from electrostatic interactions between a drifting ion and its surrounding solvent. Here, combining nanopore transport measurements over electric fields spanning several orders of magnitude with molecular dynamics simulations, we show that the time-averaged electrostatic force on a migrating ion is not a drag force but a net driving force. By contrasting charged ions with neutral particles, we reveal that ionic charge introduces additional Lorentzian peaks in the frequency-dependent friction coefficient. These peaks originate predominantly from short-range Lennard-Jones (LJ) interactions within the first hydration layer and represent additional channels for energy dissipation, strongest for Li$^+$ and progressively weaker for Na$^+$ and K$^+$. Our results demonstrate that electrostatic interactions primarily act to tighten the local hydration structure, thereby amplifying short-range LJ interactions rather than directly opposing ion motion. This microscopic mechanism provides a unified physical explanation for the breakdown of the Stokes-Einstein relation in aqueous ion transport. |
| title | A microscopic origin for the breakdown of the Stokes Einstein relation in ion transport |
| topic | Soft Condensed Matter Chemical Physics |
| url | https://arxiv.org/abs/2601.08309 |