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Cited by 13Force Microscopy Techniques and ApplicationsLubricants and Their AdditivesTribology and Lubrication Engineering

Fabrication of AFM-Compatible Hydrogel Probe to Achieve Hydration Superlubrication in Salt Solutions

Open access
Wu, Zhuolin, Zhang, Rui, Li, Jinjin·2025·Small
DOI 10.1002/smll.202411253
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Abstract

Abstract Hydrogels demonstrate effective lubricating properties, but the underlying mechanisms at the nanoscale remain elucidated. In this study, a novel strategy is proposed by fabricating the hydrogel probes compatible with atomic force microscopy (AFM) to establish a superlubrication system based on the hydration interactions. The probe is made of polyethylene glycol diacrylate (PEGDA)‐based hydrogel microspheres, which can achieve an extremely low friction coefficient of 0.0014 when sliding on the mica surface in NaCl solution. The friction coefficients in salt solutions sequence μ(NaCl) < 0.01 < μ(KCl) < μ(LiCl), which contradicts the sequence based on the ion hydration capacity (K + < Na + < Li + ), suggesting that the hydrogel‐based lubrication systems are governed by the interplay between ion hydration lubrication and ions‐polymer interactions simultaneously. The observed superlubrication in NaCl solution is ascribed to the superior hydration capacity of Na + ions, which forms a stable and smooth hydration layer within the contact zone. This work provides new avenues for AFM‐based hydrogel studies, and also significantly advances the comprehension of hydrogel lubrication mechanisms at the nanoscale

AI snapshot

Written from the paper’s full text.

TL;DR

The authors built AFM-compatible hydrogel probes from PEGDA-based microspheres and used them to study nanoscale lubrication against mica in salt solutions. The PEGDA/AM probe reached an ultralow friction coefficient in NaCl solution, which the paper attributes to a combination of ion hydration and specific ion–polymer interactions rather than hydration capacity alone.

Key findings

  • A PEGDA/AM hydrogel probe sliding on mica in 0.5 M NaCl achieved an ultralow friction coefficient reported as 0.0014 in the abstract/conclusion and 0.0015 in the load-fitting results; this was lower than PEGDA 40% (μ = 0.0057) and PEGDA 80% (μ = 0.0042), and far below the SiO₂ probe (μ = 0.1623).
  • For the hydrogel probes, friction coefficients in alkali-metal chloride solutions followed μ(NaCl) < 0.01 < μ(KCl) < μ(LiCl), which the authors note contradicts the order expected from ion hydration capacity (K⁺ < Na⁺ < Li⁺). The SiO₂ probe instead followed μ(KCl) ≈ μ(NaCl) < μ(LiCl).
  • The paper links the NaCl result to Na⁺ forming a stable, smooth hydration layer in the contact zone, while Li⁺ was easily squeezed out and K⁺ bound more strongly to oxyethylene segments, increasing shear. Supporting observations include surface roughness in LiCl and KCl about twice that in NaCl, decay lengths of 2.05 nm (LiCl), 1.78 nm (NaCl), and 1.55 nm (KCl), and much higher friction (μ > 0.1) in MgCl₂ and AlCl₃ solutions.
  • Sodium salts with different anions (NaCl, Na₂SO₄, Na₃PO₄) all gave friction coefficients between 0.001 and 0.002, suggesting anion valence had little effect and Na⁺ was the key cation.

Methods

  • Hydrogel microspheres were produced in a microfluidic device from PEGDA 40%, PEGDA 80%, and PEGDA/AM precursor solutions, photocrosslinked at 365 nm, cleaned, and attached to tipless AFM cantilevers; a spherical SiO₂ probe served as a control.
  • Friction and normal-force measurements used AFM lateral force mode on freshly cleaved mica in various salt solutions, with normal loads from 0 to 140 nN, sliding speeds of 2, 4, and 8 μm s⁻¹, a 1000 nm scan length, and 25 ± 2 °C; each set was run in triplicate with measurements at five locations.
  • Characterization included FTIR, XPS, and SEM; normal-force curves were fitted with DLVO theory; surface morphology was imaged in tapping mode; and GROMACS molecular dynamics simulations used radial distribution functions to compare cation interactions with PEGDA and AM groups.

Limitations

  • The paper does not explicitly state limitations.
  • Evident from the text: friction tests used only freshly cleaved mica as the opposing surface, so the findings are not shown to generalize to other substrates or macroscopic hydrogel contacts.
  • Evident from the text: the proposed mechanism relies on AFM force/morphology data and GROMACS simulations, with simulation details placed in Supporting Information and no independent validation of the ion–polymer interaction model reported in the main text.

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

Integrity signals

Registry

Crossref · 10.1002/smll.202411253

Cites

53 of 53 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 20 cited sources checked · 0 supported · 0 flagged

  • Findingown data

    Superlubrication with ultralow friction coefficients ranging from 0.001 to 0.003 was achieved in NaCl solutions at all three concentrations (0.1 m, 0.5 m, and 1 m).

    “The superlubrication with ultralow friction coefficients ranging of 0.001-0.003was achieved in NaCl solutions at all three concentrations.”
    Quote in the paperSubstantial claim
  • Findingcitation

    The C═CH2 twisting peak at 1410 cm−1 was absent in the FTIR spectra of all three photopolymerized hydrogels, confirming that polymerization of monomers occurred under UV irradiation.

    “The C═CH 2 twisting peak at 1410 cm -1 was absent in the spectra of all three photopolymerized hydrogels, confirming that the polymerization of monomers occurred under UV irradiation.[31]”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [31] 31. M. T. Rahman, Z. Barikbin, A. Z. M. Badruddoza, P. S. Doyle, S. A. Khan, Langmuir 2013, 29, 9535.

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

  • Findingown data

    All three types of hydrogel probes sliding against mica achieved superlubrication in 0.5 m NaCl solution when the normal load was applied from 0 to 140 nN.

    “It was found that all three types of hydrogel probes sliding against the mica achieved superlubrication in 0.5 m NaCl solution when the normal load was applied from 0 to 140 nN.”
    Quote in the paperSubstantial claim
  • Findingown data

    The PEGDA-based hydrogel microsphere probe can achieve an extremely low friction coefficient of 0.0014 when sliding on the mica surface in NaCl solution.

    “The probe is made of polyethylene glycol diacrylate (PEGDA)-based hydrogel microspheres, which can achieve an extremely low friction coefficient of 0.0014 when sliding on the mica surface in NaCl solution.”
    Quote in the paperSubstantial claim
  • Findingown data

    The friction coefficients were ≈0.01 in KCl solutions at all three concentrations.

    “The friction coefficients were ≈0.01 in KCl solutions at all three concentrations (Figure 2e).”
    Quote in the paperSubstantial claim
  • May combine two claims. 34
  • The quote only partly states this claim. 1
  • Classified as probably not a substantial claim. 11

  • May combine two claims.

    Findingown data

    For the SiO2 probe sliding against mica, μ(KCl) ≈ μ(NaCl) < μ(LiCl).

    “The friction coefficient for the SiO 2 probe sliding against the mica satisfies 𝜇(KCl) ≈𝜇(NaCl) < 𝜇(LiCl)”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    MD simulations revealed that cations on AM are primarily distributed on its carbonyl groups, and the strength of the interaction follows the order Li+ < Na+ < K+, while the amino groups on AM exhibit negligible interactions with cations.

    “The computational results revealed that cations on AM are primarily distributed on its carbonyl groups (Figure 4a), and the strength of the interaction follows the order Li + < Na + < K + , while the amino groups on AM exhibit negligible interactions with cations.”
    Quote in the paperSubstantial claim

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

    Findingown data

    The PEGDA/AM hydrogel probe achieved the lowest friction coefficient (μ = 0.0015), representing a 64.3% and 99% reduction compared to the PEGDA 80% hydrogel probe and SiO2 probe, respectively, when sliding against mica in 0.5 M NaCl solution.

    “The PEGDA/AM hydrogel probe achieved the lowest friction coefficient (𝜇 = 0.0015), representing a 64.3% and 99% reduction compared to the PEGDA 80% hydrogel probe and SiO 2 probe, respectively.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Fitting the nonlinear force curve with DLVO theory yielded decay lengths of λd = 2.05 nm in LiCl solution, λd = 1.78 nm in NaCl solution, and λd = 1.55 nm in KCl solution.

    “The fitting of the decay length in different cationic aqueous solutions yields the following values, in LiCl solution the decay length 𝜆 d = 2.05 nm, in NaCl solution the 𝜆 d = 1.78 nm, and in KCl solution the 𝜆 d = 1.55 nm.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [35] 35. J. N. Israelachvili, Intermolecular and Surface Forces, Academic press, 2011. source

  • May combine two claims.

    Findingown data

    The friction coefficients of all three hydrogel probes were <0.01 when sliding against mica in NaCl solution, significantly lower than in LiCl and KCl solutions.

    “Meanwhile, it was found that the friction coefficients of all three hydrogel probes were <0.01 when sliding against the mica in NaCl solution.This was significantly lower than the results measured in LiCl and KCl solutions.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The PEGDA 40% hydrogel probe exhibited a friction coefficient μ = 0.0057, reflecting a 96.5% reduction compared to the μ = 0.1623 of the SiO2 probe.

    “The PEGDA 40% hydrogel probe exhibited a friction coefficient of 𝜇 = 0.0057, reflecting a 96.5% reduction compared to the 𝜇 = 0.1623 of the SiO 2 probe.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    A superlubrication state was effectively achieved in all sodium salt solutions containing anions with different valences, with friction coefficients ranging from 0.001 to 0.002.

    “The results showed that a superlubrication state was effectively achieved in all these solutions, with friction coefficients ranging from 0.001 to 0.002.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The SiO2 probe could not achieve superlubrication and exhibited the highest friction coefficient, regardless of the solution environment.

    “The SiO 2 probe could not achieve superlubrication and exhibited the highest friction coefficient, regardless of the solution environment.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The friction force in MgCl2 and AlCl3 solutions both increased significantly throughout the whole loading process, and the friction coefficients all exceeded 0.1, much higher than in NaCl solution.

    “The friction force in MgCl 2 and AlCl 3 solutions both increased significantly throughout the whole loading process, and by fitting these data linearly, the friction coefficients all exceeded 0.1, which achieved much higher friction in contrast with that in NaCl solution (Figure 2g).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingreasoning

    When the PEGDA/AM probe slid against mica in KCl solution, the friction coefficient approached 0.01, which is 8 times higher than that measured in NaCl solution.

    “When the PEGDA/AM probe slid against the mica in KCl solution, the friction coefficient approached 0.01, which increased by 8 times in comparison to that measured in NaCl solution.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    A significant long-range repulsive force between the PEGDA/AM hydrogel probe and mica appeared when the separation was reduced to ≈10 nm, and the repulsive force increased exponentially as the separation was reduced.

    “A significant long-range repulsive force between the probe and mica appeared when the separation between the probe and mica was reduced to ≈10 nm, and the repulsive force increased exponentially as the separation was reduced.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Both the oxy-ethylene segments and carbonyl groups on the PEGDA/AM hydrogel have the ability to bind cations, but the RDF peak for the oxy-ethylene segments is more pronounced.

    “Both the oxy-ethylene segments and carbonyl groups on the PEGDA/AM hydrogel have the ability to bind cations, but the RDF peak for the oxy-ethylene segments is more pronounced.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    A grid-like structure is observed on the surface of the PEGDA/AM hydrogel probe in pure water, whereas this structure is absent in salt solutions.

    “Grid-like structure is observed on the surface in pure water (Figure S4, Supporting Information) whereas this structure is absent in salt solutions.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    In LiCl solutions, the PEGDA/AM hydrogel probe exhibited the highest friction coefficients (μ > 0.02) across all three concentrations, comparable to the friction coefficient measured in a water environment.

    “In LiCl solutions, it exhibited the highest friction coefficients (𝜇 > 0.02) across all three concentrations, which were comparable to the friction coefficient measured in a water environment.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    In 0.5 m NaCl solution, no significant difference was observed in friction behavior across the tested sliding speeds, with friction coefficients remaining ≈0.0015.

    “In the 0.5 m NaCl solution, no significant difference was observed in friction behavior across the tested sliding speeds, with friction coefficients remaining ≈0.0015.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    In 0.5 m LiCl and 0.5 m KCl solutions, the friction coefficients had a slight increase with increasing sliding speeds, but superlubrication cannot be achieved in KCl and LiCl solutions for all sliding speeds.

    “The results obtained in the 0.5 m LiCl and 0.5 m KCl solutions showed that the friction coefficients had a slight increase with sliding speeds increasing, but the superlubrication cannot be achieved in KCl and LiCl solutions for all sliding speeds.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingreasoning

    Under the combined influence of ionic hydration capability and ions-polymer interactions, the friction force and coefficient measured for hydrogel-mica friction pairs in Na+ ions solution were lower than those observed in Li+ and K+ solutions, achieving a superlubrication state with an ultralow friction coefficient of 0.0014.

    “Under the combined influence of ionic hydration capability and ions-polymer interactions, the friction force and coefficient measured for the hydrogel-mica friction pairs in Na + ions solution were lower than those observed in Li + ions and K + ions solutions, achieving a superlubrication state with an ultralow friction coefficient of 0.0014.”
    • Also stated in: § 3. Conclusion · plain
      “which achieved superlubrication with an ultralow friction coefficient of 0.0014 in NaCl solution.”
    Quote in the paperSubstantial claim

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

    Findingnone given

    The hydrogel surface possesses a porous structure rather than the smooth, flat characteristics of the mica surface.

    “Given that the hydrogel surface possesses a porous structure rather than the smooth, flat characteristics of the mica surface, some oxy-ethylene segments on the hydrogel surface inevitably come into contact with the cations that have accumulated on the mica surface in the lubricated contact zone.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Oxyethylene segments interact specifically with hydrated alkali metal cations, and this interaction is influenced by the physicochemical properties of the polymer and the ions in the solution.

    “The oxyethylene segments interact specifically with hydrated alkali metal cations, and this interaction is influenced by the physicochemical properties of the polymer and the ions in the solution.[43][44][45][46][47]”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [43][44][45][46][47]

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

  • May combine two claims.

    Interpretationreasoning

    The enhanced interaction between K+ ions and oxyethylene segments in the hydrogel probe results in increased shear strength, which explains why the lubrication state in K+ solutions resembles that in Na+ solutions but fails to achieve superlubrication.

    “This enhanced interaction would result in the increase of shear strength, which is the reason that the lubrication state of the contact zone observed in K + ions solutions resembles that in Na + ions solutions but fails to achieve superlubrication (Figure 4f).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    The valence of the cation affects the superlubrication performance, further demonstrating that Na+ ions are the crucial factor for achieving superlubrication between the hydrogel probe and mica.

    “This suggests that the valence of the cation affects the superlubrication performance, further demonstrating Na + ions are the crucial factor for achieving superlubrication between the hydrogel probe and mica.”
    Quote in the paperSubstantial claim

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

    Premisecitation

    Previous research on mica-mica friction pairs suggested that the friction coefficient followed the trend μ(KCl) ≤ μ(NaCl) < μ(LiCl) due to hydration lubrication.

    “Previous research on mica-mica friction pairs suggested that the friction coefficient followed the trend 𝜇(KCl) ≤ 𝜇(NaCl) < 𝜇(LiCl) due to hydration lubrication.[33]”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [33] 33. A. Gaisinskaya-Kipnis, L. Ma, N. Kampf, J. Klein, Langmuir 2016, 32, 4755.

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

  • May combine two claims.

    Interpretationreasoning

    The stronger interaction between the hydrogel probe and Na+ ions promotes the formation of a robust and smooth hydrated ionic layer on the surface of the PEGDA/AM hydrogel probe, which results in a decrease in the surface roughness on the hydrogel microsphere.

    “The stronger interaction between the hydrogel probe and Na + ions promotes the formation of a robust and smooth hydrated ionic layer on the surface of the PEGDA/AM hydrogel probe, which would result in a decrease in the surface roughness on the hydrogel microsphere.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    The shear process encountered a low energy barrier, which enabled the maintenance of extremely low shear strength to achieve a superlubrication state.

    “The shear process encountered a low energy barrier, which enabled the maintenance of extremely low shear strength to achieve a superlubrication state.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Interpretationreasoning

    The unique interactions between the polymer in the hydrogel and salt ions may influence the realization of hydration-based superlubrication, potentially promoting or inhibiting it.

    “Specifically, the unique interactions between the polymer in the hydrogel and salt ions may influence the realization of hydration-based superlubrication, with these interactions potentially promoting or inhibiting the hydration superlubrication.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationcitation

    K+ ions directly bind to the oxyethylene segments on the polymer chain, and this direct interaction allows K+ ions to compete with water molecules for binding sites on the polymer chain.

    “The K + ions directly bind to the oxyethylene segments on the polymer chain, and this direct interaction allows K + ions to compete with water molecules for binding sites on the polymer chain.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    Changes in anion valence have minimal impact on the frictional properties of the system, supporting that Na+ ions are a crucial factor for achieving superlubrication between the hydrogel probe and mica.

    “This indicates that the changes in anion valence have minimal impact on the frictional properties of the system, supporting Na + ions are a crucial factor for achieving superlubrication between the hydrogel probe and the mica.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Although the salt ions undergo hydration, a specific interaction between Na+ ions and the hydrogel promotes the achievement of superlubrication, whereas the interaction between Li+ and K+ ions and hydrogel appears to inhibit the occurrence of superlubrication.

    “According to the results of surface morphology and normal force interaction, it can be inferred that, although the salt ions undergo hydration, a specific interaction between Na + ions and the hydrogel promotes the achievement of superlubrication.In contrast, the interaction between Li + and K + ions and hydrogel appears to inhibit the occurrence of superlubrication.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationcitation

    The observed decay lengths significantly deviate from the theoretical Debye length κ−1, primarily attributed to strong ionic correlations present in highly concentrated salt solutions.

    “These observed decay length 𝜆 d significantly deviate from the theoretical Debye length 𝜅 -1 , which is primarily attributed to the strong ionic correlations present in highly concentrated salt solutions.[36][37][38]”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [36][37][38]

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

  • May combine two claims.

    Interpretationown data

    The hydrated Li+ ions cannot stably remain within the contact zone and are easily squeezed out of the contact zone.

    “This indicates that the hydrated Li + ions cannot stably remain within the contact zone, which are easily squeezed out of the contact zone.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    The normal force curve results indicate that a large number of hydrated Li+ ions were squeezed from the contact zone, further suggesting that the binding strength between hydrated Li+ ions and the hydrogel surface is insufficient to maintain their stable presence in the contact zone.

    “Additionally, the normal force curve results indicate that a large number of hydrated Li + ions were squeezed from the contact zone, further suggesting that the binding strength between hydrated Li + ions and the hydrogel surface is insufficient to maintain their stable presence in the contact zone.”
    Quote in the paperSubstantial claim

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

    Study design and conductnone given

    In friction force and normal force measurements, each experimental set was conducted in triplicate, utilizing freshly prepared mica substrates and probes for each repetition.

    “In the friction force and normal force measurements, each experimental set was conducted in triplicate, utilizing freshly prepared mica substrates and probes for each repetition.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning

    The effect of hydration on lubrication performance in hydrogel-involved systems within salt solutions is influenced not only by the strength of ion hydration but also by the presence of hydrophilic groups on the hydrogel surface.

    “It is worth noting that the effect of hydration on lubrication performance in hydrogel-involved systems within salt solutions is influenced not only by the strength of ion hydration but also by the presence of hydrophilic groups on the hydrogel surface.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S2 (checkable). May combine two claims.

    Interpretationreasoning

    This work enhances the understanding of hydrogel lubrication mechanisms at the nanoscale, which holds potential applications for the design of efficient hydrogel-based lubrication systems.

    “This work enhances the understanding of hydrogel lubrication mechanisms at the nanoscale, which holds potential applications for the design of efficient hydrogel-based lubrication systems.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Study design and conductcitation

    The frictional force for each applied load was determined by the half width of a full force loop and the lateral sensitivity, with eight friction loops of the same load averaged.

    “The frictional force for each applied load was determined by the half width of a full force loop and the lateral sensitivity, with eight friction loops of the same load averaged.[54]”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [54] 54. J. Li, W. Cao, J. Li, M. Ma, J. Colloid Interface Sci. 2021, 596, 44.

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

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

    Interpretationnone given

    The interaction strength between Na+ ions and oxy-ethylene segments is intermediate, lying between that of K+ ions and Li+ ions.

    “Second, the interaction strength between Na + ions and oxy-ethylene segments is intermediate, lying between that of K + ions and Li + ions.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning

    The developed AFM-compatible hydrogel probes are versatile, allowing for the adjustment of properties such as type, mechanical characteristics, and surface functional groups according to the specific requirements of experiment, which offers a new method into the study of the microstructural characteristics and lubrication mechanisms of flexible lubricating materials like hydrogels at the nanoscale

    “Moreover, the developed AFM-compatible hydrogel probes are versatile, allowing for the adjustment of properties such as type, mechanical characteristics, and surface functional groups according to the specific requirements of experiment, which offers a new method into the study of the microstructural characteristics and lubrication mechanisms of flexible lubricating materials like hydrogels at the”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    Using hydrogel probes, a hydration lubrication system could be established at the nanoscale, which provides a positive method to reveal the lubrication mechanisms of hydrogels in salt solution.

    “Using the hydrogel probes, a hydration lubrication system could be established at the nanoscale, which provides a positive method to reveal the lubrication mechanisms of hydrogels in salt solution.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    The hydrophilic groups (-NH2) in the PEGDA/AM hydrogel probe enhance its hydrophilicity, promote the formation of a stable hydration layer, and improve the lubrication state, leading to a friction coefficient lower than that of PEGDA 40% and PEGDA 80% hydrogel probes.

    “which could enhance its hydrophilicity, promote the formation of a stable hydration layer, and improve the lubrication state, leading to the friction coefficient being lower than the PEGDA 40% and PEGDA 80% hydrogel probes (Figure 2c).”
    Quote in the paperSubstantial claim

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

    Interpretationnone given

    Na+ ions can form a stable hydrated ions layer due to their relatively high hydration capacity.

    “First, Na + ions can form a stable hydrated ions layer due to their relatively high hydration capacity.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: Na+ ions have relatively high or superior hydration capacity.

  • Classified as probably not a substantial claim.

    Study design and conductcitation

    The normal spring constant and lateral sensitivity of the probe were determined using the thermal noise method and the diamagnetic lateral force calibrator method prior to each test.

    “The normal spring constant and lateral sensitivity of the probe were determined using the thermal noise method and the diamagnetic lateral force calibrator method prior to each test.[52]”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [52] 52. Q. Li, K.-S. Kim, A. Rydberg, Rev. Sci. Instrum. 2006, 77, 065105.

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

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

    Study design and conductnone given

    Molecular dynamics simulations employed the time-averaged sampling statistical method.

    “Molecular dynamics simulations employed the time-averaged sampling statistical method.”
    Quote in the paperNot a substantial claim

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

    Study design and conductreasoning

    To ensure reliability and minimize random errors, measurements were performed at five distinct locations on the mica substrate during each experiment.

    “To ensure the reliability of the results and minimize random errors, measurements were performed at five distinct locations on the mica substrate during each experiment.”
    Quote in the paperNot a substantial claim
43 of 43

  • The paper relies on this without support.

    The mica surface is negatively charged.

    “leaving only one layer of hydrated Li + ions adsorbed on the negatively charged mica surface.”

  • The paper relies on this without support.

    The ion hydration capacity sequence is K+ < Na+ < Li+.

    “which contradicts the sequence based on the ion hydration capacity (K + < Na + < Li + ).”

  • The paper relies on this without support.

    Na+ ions have relatively high or superior hydration capacity.

    “The superior hydration capacity of Na + ions, coupled with their stronger interaction with oxy-ethylene segments in hydrogel, enables the formation of stable hydration layer on the surface of hydrogel microsphere.”
3 of 3

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • PEGDA is identified as two different compounds

    Minor

    The paper expands PEGDA as polyethylene glycol diacrylate, but the Materials section identifies the purchased PEGDA as poly(ethylene glycol) dimethacrylate. Diacrylate and dimethacrylate are different compounds, so the material used is internally unclear.

1 of 1

Cites

Flagged first, then by citations

Research works printed but not linked: 2

  1. Li W., 2022, Innovation, 3
  2. Von Hippel P., 1969, Struct. Stability Biol. Macromolecules, 2, 417

Cited by

Sorted by citations

Related

Authors
Wu, Z., Zhang, R., & Li, J.
Affiliations
State Key Laboratory of Tribology (CN)
Corresponding author
Li, Jinjin
ORCID
Venue
Small
Publisher
Wiley
Published
2025-01-28
Volume
21
Issue
31
Pages
e2411253-e2411253
ISSN
  • 1613-6810 (ISSN-L)
  • 1613-6829
DOI
10.1002/smll.202411253
OpenAlex
W4406918501
Cited by
13
References
53
Citations by year
2026: 10 · 2025: 3
FWCI
4.74
Type
journal article
Language
en
Open access
Licence
onlinelibrary.wiley.com/termsAndConditions#vor (vor)
Locations
  • Small (publishedVersion)
  • PubMed (publishedVersion)
Funders
  • National Key Research and Development Program of China (2020YFA0711003)
  • National Natural Science Foundation of China (52175174, U2268212)
Topics
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Force Microscopy Techniques and Applications
  • Physical Sciences › Engineering › Mechanical Engineering › Lubricants and Their Additives
  • Physical Sciences › Engineering › Mechanical Engineering › Tribology and Lubrication Engineering
Keywords
superlubricity, salt solutions, ion hydration, friction coefficient, sodium chloride, KCl, lithium chloride, ion-polymer interactions, hydration shell, mica surface

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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 ›

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