CoChat
Sign Up
Cited by 30Lubricants and Their AdditivesForce Microscopy Techniques and ApplicationsElectrostatics and Colloid Interactions

Probing the hydration friction of ionic interfaces at the atomic scale

Open access
Li, Zibo, Liu, Qian, Zhang, Deliang, Wang, Yin, Zhang, Yuge, Li, Qiang, Dong, Mingdong·2022·Nanoscale Horizons
DOI 10.1039/d1nh00564b
Open this paper in CoChat — free accountOpen PDF

Abstract

, which contrasts with the Hofmeister series, indicating that the hydration friction depends not only on the hydration strength of the alkali cations but also on the arrangement of the alkali cations at the interface. The results of this study provide deep insights into the origins of hydration friction, with potential implications for the development of new boundary lubrication in aqueous media.

AI snapshot

Written from the paper’s full text.

TL;DR

This study combines 3D atomic force microscopy and friction force microscopy to map hydration layers and measure friction on mica in alkali chloride solutions. It reports that hydration friction depends on ion identity and concentration, with high salt concentrations producing lower friction coefficients than low concentrations.

Key findings

  • At 200 mM, LiCl, NaCl, and KCl form an atomic-scale corrugation with ~0.52 nm periodicity, a Stern layer of ~0.4 nm for Li⁺, Na⁺, and K⁺ and ~0.3 nm for Cs⁺, plus two thin hydration layers above; CsCl shows weaker hydration with a smaller second-layer separation and an almost invisible third layer.
  • At 4 M, all salts form an epitaxial crystal-like nanostructure with alternating cation and anion layers and ~0.52 nm lateral periodicity; force curves show three stronger repulsive peaks, and the peak separations become nearly equal across salts (e.g., LiCl d₀ = 0.281 ± 0.01 nm, d₁ = 0.361 ± 0.03 nm, d₂ = 0.343 ± 0.04 nm; CsCl d₀ = 0.260 ± 0.01 nm, d₁ = 0.358 ± 0.03 nm, d₂ = 0.345 ± 0.05 nm).
  • Friction coefficients followed K⁺ < Na⁺ < Li⁺ < Cs⁺, contrary to a Hofmeister-like expectation; high-concentration solutions had lower friction coefficients than low-concentration ones, and pure water gave the highest friction among the compared liquids.
  • Peak hydration forces were larger at 4 M than at 200 mM and differed less between ions at high concentration; energy dissipation and mean friction peak force both decreased at high concentration.

Methods

  • Muscovite mica was probed in LiCl, NaCl, KCl, and CsCl solutions at 200 mM and 4 M, plus pure water; salts were ≥99.9% and water was 18.0 MΩ ultrapure.
  • Hydration-layer imaging used a Cypher ES AFM with gold-coated silicon cantilevers, photothermal excitation, a 6 N m⁻¹ spring constant, and 450 kHz resonance; force curves were obtained in FM-AFM mode, with 50 Δf curves averaged and converted to force.
  • Friction measurements used a Cypher ES AFM with MSNL-10 cantilevers (normal spring constant ~0.02 N m⁻¹, lateral ~14 N m⁻¹), scanning 10 nm × 10 nm at 10 Hz, with a maximum normal force of 500 pN; friction coefficients came from linear fits of friction versus load, and Hertz contact theory estimated maximum pressures of ~80 MPa at 200 mM and ~35 MPa at 4 M.

Limitations

  • The paper states no explicit limitations.
  • Evident from the text: the study is restricted to muscovite mica, four alkali chloride salts, two concentrations (200 mM and 4 M), and pure water, so generalization to other surfaces, ions, mixed electrolytes, or intermediate concentrations is not established.
  • Evident from the text: the friction interpretation relies on peak hydration forces extracted from trace Δf curves and a proposed energy barrier for hydrated cations on the tip and mica; the contact pressures also differ between the low- and high-concentration measurements (~80 MPa versus ~35 MPa), which may complicate direct comparison.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1039/d1nh00564b

Cites

52 of 52 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 17 cited sources checked · 0 supported · 0 flagged

  • Findingreasoning

    The COFs of electrolyte solutions at high concentrations are obviously smaller than those in low concentrations.

    “Therefore, the COFs of electrolyte solutions at high concentrations are obviously smaller than those in low concentrations, as shown in Fig. 4D.”
    Quote in the paperSubstantial claim
  • Findingown data

    Atomic-scale friction mappings of mica in different electrolyte solutions were obtained through FFM.

    “Atomic scale friction mappings of mica in different electrolyte solutions were obtained through FFM, and the hydration lubrication effects of different alkali cations were well explained by combining the hydration forces.”
    Quote in the paperSubstantial claim
  • Findingown data

    The less strongly hydrated Na+ and K+ exhibit lower peak hydration forces in sequence.

    “The less strongly hydrated Na + and K + exhibit lower peak hydration forces (Fig. 4E) in sequence.”
    Quote in the paperSubstantial claim
  • Findingown data

    The dot-like pattern in the friction mapping of KCl solution (200 mM) is arranged as a hexagonal structure with a periodicity of about 0.51 nm, corresponding to the atomic-scale corrugation at the bottom of the hydration layer map.

    “The dot-like pattern in Fig. 4A is arranged as a hexagonal structure with a B0.51 nm periodicity, which corresponds to the atomic scale corrugation at the bottom of the hydration layer map (Fig. 2A-D).”
    Quote in the paperSubstantial claim
  • Findingown data

    The frictional energy dissipation when the AFM tip slides across the mica surface with different hydrated cations differs considerably depending on the ion species and concentrations.

    “The most important finding in this study is that the frictional energy dissipation, when the AFM tip sliding across the mica surface with different hydrated cations, is considerably differed depending on the ion species and concentrations.”
    Quote in the paperSubstantial claim
  • May combine two claims. 17
  • The quote only partly states this claim. 2
  • Classified as probably not a substantial claim. 4

  • May combine two claims.

    Findingown data

    In a high concentration solution, the difference between the trace and retrace friction signals decreases compared with that of a low concentration solution, indicating less energy dissipation.

    “It can be seen that, in the case of a high concentration solution, the difference between the trace and the retrace friction signals decreases compared with the that of a low concentration solution, which indicates less energy dissipation.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The repulsive region in the force curves corresponds to the adsorbed cation layer and local hydration layer, and the repulsive peak force decreases as the order of the hydration layer increases.

    “The repulsive region corresponds to the adsorbed cation layer and local hydration layer, and the repulsive peak force decreases as the order of hydration layer increases.”
    Quote in the paperSubstantial claim

  • May combine two claims. The quote only partly states this claim.

    Findingown data

    At low concentration, the force curves for Li+ and Na+ have a clear tendency to bend to the left at the leftmost end, while those for K+ and Cs+ do not.

    “Moreover, at the leftmost end of the force curves of Li + and Na + , the force curves have a clear tendency to bend to the left (the part framed by a red dashed rectangle in Fig. 2I and J), which may be caused by the detachment of cations from the mica surface as the force increases.But that's not the case with the force curves for K + and Cs + .”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Li+, Na+, and K+ have a stronger hydration strength than Cs+.

    “This result proves that Li + , Na + , and K + have a stronger hydration strength.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingcitation

    The high-concentration nanostructure is an epitaxial growth from the mica lattice with a lateral periodicity of about 0.52 nm, consisting of alternated cation and anion layers parallel to the mica surface, with significant water to balance electrostatic interactions and stabilize the nanostructure.

    “This nanostructure is an epitaxial growth from the mica lattice with a lateral periodicity of B0.52 nm.It consists of alternated cation and anion layers parallel to the mica surface, and there is still a significant amount of water to balance the electrostatic interactions and stabilize the nanostructure.22”
    • Also stated in: § Conclusions · plain
      “At high concentrations (4 M), the cations and anions alternate epitaxial growth on the mica lattice.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [22] 22. D. Martin-Jimenez, E. Chacon, P. Tarazona and R. Garcia, Nat. Commun., 2016, 7, 12164.

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Findingown data

    The force curves for LiCl, NaCl, and KCl exhibit three obvious peak forces, while the force curves for CsCl and pure water exhibit two reduced peak forces.

    “The force curves belonging to LiCl, NaCl, and KCl exhibit three obvious peak forces, while the force curves of CsCl and pure water exhibit two reduced peak forces.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    At high concentrations, the peak hydration forces are much stronger than those at low concentrations, and the difference of hydration repulsion between different ions is reduced.

    “At high concentrations, the peak hydration forces are much stronger than those at low concentrations, and the difference of hydration repulsion between different ions is also reduced, as shown in Fig. 4F.”
    • Also stated in: § Conclusions · plain
      “In addition, the hydration force was found to be much higher at high concentrations than at low concentrations.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S1 (asserted), S4 (based).

    Findingnone given

    The COFs of different electrolyte solutions follow the sequence μ_K+ < μ_Na+ < μ_Li+ < μ_Cs+.

    “However, in this work, the COFs of different electrolyte solution suggest a disordered sequence: m K+ o m Na+ o m Li+ o m Cs+ , as shown in Fig. 4D.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    At 200 mM, the CsCl hydration layer mapping differs from those of LiCl, NaCl, and KCl: the separation between the second hydration layer and the Cs+ layer is much smaller, and the third hydration layer is barely visible.

    “The hydration layer mapping of the CsCl solution (Fig. 2D) shows a significant difference compared with those of the cations mentioned above.The separation between the second hydration layer and the Cs + layer is much smaller, and the third hydration layer is barely visible.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The slope of the friction-load force curve for a high concentration solution is smaller than that for a low concentration solution, indicating that COFs are lower at high electrolyte concentration.

    “As can be seen from the curves, the slope of a high concentration solution is smaller than that of a low concentration one, which indicates that the COFs are lower in a high electrolyte concentration.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingreasoning

    At high salt concentrations, the force curves exhibit three stronger peak forces compared with those at low salt concentrations, and the leftmost end of all the force curves has no tendency to bend to the left.

    “At high salt concentrations, the force curves exhibit three stronger peak forces compared with those at low salt concentrations, and the leftmost end of all the force curves has no tendency to bend to the left.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Study design and conductnone given

    A defect in Fig. 3B supports the reliability and accuracy of the experimental test.

    “It is worth noting that there is a defect (marked by the white dashed circle) in Fig. 3B, which proves the reliability and accuracy of our experimental test.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationcitation

    For cations with a larger hydration capacity (Li+, Na+, and K+), plenty of water molecules are hydrated with these cations and they have a great fluid response to the slipped tip; the hydrated cations can resist rigid contact between the sliding tip and mica, leading to a lower COF.

    “For the cations with a larger hydration capacity (Li + , Na + , and K + ), plenty of water molecules are hydrated with these cations and they have a great fluid response to the slipped tip.The hydrated cations can resist the rigid contact between the sliding tip and mica.7 Thus, these hydrated cations have some degree of hydration lubrication, which leading to a lower COF (Fig. 4D).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [7] 7. A. Gaisinskaya-Kipnis, L. Ma, N. Kampf and J. Klein, Lang- muir, 2016, 32, 4755-4764.

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Interpretationreasoning

    Cs+ has a smaller peak hydration force and shows a higher COF compared with Li+, Na+, and K+, because very few water molecules are hydrated with Cs+, giving little fluid response to the slipped tip.

    “While in the case of Cs + , the hydrated Cs + has a smaller peak hydration force, and shows a higher COF compared with those of Li + , Na + and K + .That is because there are very few water molecules hydrated with Cs + , which thus has little fluid response to the slipped tip.”
    • Also stated in: § Conclusions · plain
      “Cs + showed a higher COF due to the weak hydration capacity to prevent rigid coupling between the tip and mica.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    Friction tests were conducted in a random sequence to exclude the potential impact of systematic change.

    “It should be noted that in order to exclude the potential impact of systematic change, the friction tests were conducted in a random sequence.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning

    At low concentrations, Li+ has larger peak hydration forces, leading to greater frictional energy dissipation for the distortion of hydrated Li+ as the AFM tip slides past on the mica surface.

    “At low concentrations, Li + has the larger peak hydration forces, leading to a greater frictional energy dissipation for the distortion of hydrated Li + , as the AFM tip slides past on the mica surface.”
    • Also stated in: § Conclusions · boosted
      “At low concentrations, Li + caused the strongest resistance to tip slip due to the strongest hydration repulsion, followed by Na + and K + .”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    At high concentration, many more ions assemble on the mica surface and form a more stable hydration layer.

    “This phenomenon indicates that at a high concentration many more ions assemble on the mica surface and form a more stable hydration layer.”
    Quote in the paperSubstantial claim

  • May combine two claims. The quote only partly states this claim.

    Interpretationown data

    All electrolyte solutions at high concentration can form an epitaxial growth nanostructure, which guarantees a great fluid response to the slipped tip and resists rigid contact between the tip and mica.

    “As shown in Fig. 3A-D, all the electrolyte solutions can form an epitaxial growth nanostructure, which guarantees a great fluid response to the slipped tip and resist rigid contact between the tip and mica.”
    • Also stated in: § Conclusions · plain
      “At high concentrations, the electrolyte solution showed a much better lubrication effect relative to those in low concentrations, because the alkali cations in the epitaxial growth nanostructure provide a great fluid response to the slipped tip.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Study design and conductcitation

    The peak hydration force values are comparable with previous literature, which supports the reliability of the experiment.

    “These values of the peak hydration force are comparable with the results reported in previous literature, 21 which proves the reliability of our experiment.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [21] 21. T. Fukuma, B. Reischl, N. Kobayashi, P. Spijker, F. F. Canova, K. Miyazawa and A. S. Foster, Phys. Rev. B: Condens. Matter Mater. Phys., 2015, 92, 155412.

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Classified as probably not a substantial claim. May combine two claims.

    Study design and conductnone given

    Friction force mappings were obtained with an increased load force to calculate COFs, and extrinsic factors such as experimental environment, AFM tip, and scan speed were kept constant.

    “Friction force mappings are obtained with an increased load force to calculate the COFs, and extrinsic factors, such as experimental environment, AFM tip, and scan speed are kept constant.”
    Quote in the paperSubstantial claim
20 of 20

  • The paper relies on this without support.

    Some hydrated cations are adsorbed on the negatively charged AFM tip.

    “The hydrated cations are strongly located on the mica lattice sites, and simultaneously some hydrated cations are also absorbed on the negatively charged AFM tip.”

  • The paper relies on this without support.

    The mica surface is atomically flat and net negatively charged.

    “The hydrophilic mica surface is the most commonly used substrate to establish a solid-liquid interface model owing to its atomically flat and net negatively charged surface.”

  • The paper relies on this without support.

    Electrostatic interactions between alkali cations and the interface charge of mica favor the attachment of the cations to mica.

    “The electrostatic interactions between the alkali cations and interface charge of mica favors their attachment.”
3 of 3

Cites

Flagged first, then by citations

Cited by

Sorted by citations

Related

Authors
Li, Z., Liu, Q., Zhang, D., Wang, Y., Zhang, Y., Li, Q., & Dong, M.
Affiliations
  • Shandong University (CN)
  • Aarhus University (DK)
Corresponding author
  • Li, Qiang
  • Dong, Mingdong
ORCID
Venue
Nanoscale Horizons
Publisher
Royal Society of Chemistry (RSC)
Published
2022
Volume
7
Issue
4
Pages
368-375
ISSN
  • 2055-6756 (ISSN-L)
  • 2055-6764
DOI
10.1039/d1nh00564b
OpenAlex
W4211196440
Cited by
30
References
52
Citations by year
2026: 6 · 2025: 2 · 2024: 9 · 2023: 7 · 2022: 6
FWCI
2.26
Type
journal article
Language
en
Open access
Licence
rsc.li/journals-terms-of-use (am, 405 d)
Locations
  • Nanoscale Horizons (publishedVersion)
  • PubMed (publishedVersion)
Funders
  • Det Frie Forskningsråd (9040-00219B)
  • Taishan Scholar Foundation of Shandong Province
  • Shandong University
  • Natural Science Foundation of Shandong Province (ZR2021QB045)
  • China Postdoctoral Science Foundation (2019M662325)
Topics
  • Physical Sciences › Engineering › Mechanical Engineering › Lubricants and Their Additives
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Force Microscopy Techniques and Applications
  • Physical Sciences › Chemistry › Physical and Theoretical Chemistry › Electrostatics and Colloid Interactions
Keywords
Hofmeister series, alkali metal cations, cation ordering, boundary lubrication, aqueous lubrication, atomic-scale interface structure
MeSH terms
Cations, Electrolytes, Lubrication, Friction, Microscopy, Atomic Force

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-11.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-11.

Statistics and arithmetic are recomputed, not judged.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

What counts as a claim ›How we measure confidence ›How we check this ›

Are you an author, or do you see a problem with this page? Request a review