Pith. sign in

REVIEW 4 major objections 4 minor 34 references

Shear-mode Direct Piezoelectric Response of Ferroelectric Nematic Liquid Crystals

T0 review · 4 major / 4 minor · reviewed 2026-07-31 · deepseek-v4-flash

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗

Pith's one-line read Oscillatory shear of ferroelectric nematic liquid crystals produces a direct piezoelectric current, and the authors extract the first quantitative shear-mode constants, about 0.5 µC/N for RM734 and 0.8 µC/N for DIO.

desk verdict First quantitative direct shear piezoelectric constants for ferroelectric nematics, undermined by the paper's own domain-cancellation argument and an internal temperature inconsistency. read the letter →

arxiv 2607.23297 v1 pith:IVUZWW2V submitted 2026-07-25 cond-mat.soft

Péter Salamon , Marcell Tibor Máthé , Hiroya Nishikawa , Fumito Araoka , Antal Jákli This is my paper
classification cond-mat.soft PACS 77.65.-j61.30.-v
keywords ferroelectricnematicliquidcrystalsdirectpiezoelectriceffectshear-modeconstantRM734DIOoscillatoryrheometryflowalignmentviscoelasticity
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This paper reports the first quantitative measurements of shear-mode direct piezoelectricity in ferroelectric nematic liquid crystals — fluids that are both ferroelectric and freely flowing. By shearing films of RM734 and DIO between plates while measuring the induced electric current and the complex viscosity, the authors obtain direct piezoelectric constants γ1,13 ≈ 0.5 µC/N and ≈ 0.8 µC/N, values one to two orders of magnitude above earlier converse piezoelectric measurements. They propose that flow alignment rotates the polarization toward the electrodes, generating the current, and note that the measured currents are still three to four orders below the theoretical maximum because oppositely polarized domains cancel. If the interpretation holds, these are the first quantitative direct piezoelectric coefficients for a true liquid, with immediate implications for flexible sensors and mechanical energy harvesting.

What carries the argument

The central object is the shear-mode piezoelectric charge constant γ1,13, one of the three allowed tensor components in the C∞v ferroelectric nematic phase. The load-bearing identity is Eq. (1), γ1,13 = 3 I1f h / (2π³ f² D³ Δφ |η*|), which converts the measured first-harmonic current I1f, the complex viscosity |η*| from oscillatory rheometry, and the geometry (gap h, plate diameter D, strain amplitude Δφ) into a piezoelectric constant. The proposed mechanism is flow alignment: oscillatory shear rotates the director and the ferroelectric polarization toward the electrodes, producing a periodic bound charge that is read as an electric current.

What would settle it

Measure the first-harmonic shear current on a DC-poled, uniformly oriented sample of RM734 at 128 °C, 10 Hz, and 1 mrad: a jump toward the estimated 0.3 mA would confirm the cancellation explanation and the piezoelectric assignment, while a small change would show that Eq. (1) is not isolating a pure piezoelectric current.

Watch

Extended reading notes

Core claim

The paper claims that the first-harmonic current induced by low-frequency oscillatory shear in ferroelectric nematic phases is a direct piezoelectric response, and that its amplitude, combined with the complex shear viscosity, yields the shear-mode piezoelectric charge constant through Eq. (1). Applied to the two archetypal compounds, the numbers are γ1,13 ≈ 0.5 µC/N for RM734 at 128 °C and ≈ 0.8 µC/N for DIO at 68 °C. These values are one to two orders above earlier converse piezoelectric values at higher frequencies; the authors attribute the gap to strong frequency dependence. They further argue from the second-harmonic signal that the director rotates substantially at larger strains whil

Load-bearing premise

The claim rests on treating the entire measured first-harmonic current as a uniform piezoelectric response in Eq. (1), even though Section IV explains the small current by cancellation of oppositely polarized domains — so the extracted constants are lower bounds if domains cancel and upper bounds if ionic or contact artifacts contribute.

Editorial extensions

If this is right

  • The measured values, γ1,13 ≈ 0.5 µC/N (RM734) and ≈ 0.8 µC/N (DIO), make ferroelectric nematic fluids the first liquids with quantified direct shear piezoelectricity, with constants in the range of strong solid piezoelectrics.
  • Because the response is set by flow alignment rather than a crystalline lattice, it should persist in free-flowing films and scale with electrode area, pointing to flexible, large-area sensors and mechanical energy harvesters.
  • The paper's estimate that a uniformly poled film could produce about 0.3 mA at 10 Hz — three to four orders of magnitude above the observed tens of nanoamperes — implies large practical headroom if domain cancellation can be suppressed.
  • The 1/f² dependence in Eq. (1) reconciles the much larger direct constants at low frequency with the smaller converse constants measured at higher frequency, predicting convergence if both are measured at the same frequency.
  • The enhanced current near the N–NF and SmZA–NF transitions indicates that operating near these transitions could boost the direct piezoelectric response.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • If the cancellation interpretation is right, the reported constants are lower bounds on the single-domain piezoelectric coefficient; the true value could be far larger, closer to the macroscopic polarization per unit shear stress.
  • A test the paper leaves implicit: shear the same material before and after DC poling. A large jump in first-harmonic current would confirm both the flow-alignment mechanism and the domain-cancellation explanation; no jump would suggest Eq. (1) is an aggregate fit rather than a clean piezoelectric measurement.
  • The sharp peaks in I1f at the SmZA–NF and N–NF transitions suggest the phase transition itself could be used as a tunable amplifier of the direct response, a prediction testable by mapping γ1,13 across the transition under controlled ionic content.
  • Because the units of the piezoelectric coefficient and second-harmonic generation coefficients coincide, in situ optical SHG during shear could independently monitor the director tilt angle that the electrical measurement only infers.
Share X Bluesky LinkedIn Reddit HN

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

4 major / 4 minor

Summary. The manuscript reports oscillatory shear-induced electric current measurements on the ferroelectric nematic compounds RM734 and DIO, combined with oscillatory rheometry, and uses Eq. (1) to convert the first-harmonic current amplitude into the shear-mode direct piezoelectric constant γ1,13. The authors obtain ≈0.5 µC/N (RM734 at 128 °C) and ≈0.8 µC/N (DIO at 68 °C), claim these are the first quantitative direct piezoelectric constants for NF fluids, and find them one to two orders of magnitude larger than converse-derived values. They also report temperature, frequency, and strain dependences of first and second harmonic currents, rheological data, and optical observations, and propose a flow-alignment mechanism.

Significance. The claim is significant: if correct, it would provide the first quantitative direct shear-mode piezoelectric constants for ferroelectric nematic fluids, with values far above typical converse piezoelectric constants. The experimental concept is sound and the derivation of Eq. (1) is transparent; recomputing from the stated values reproduces the quoted numbers. The simultaneous measurement of I2f and the optical null result provide useful internal diagnostics. However, the headline quantitative claim is not supported as written because Eq. (1) treats the measured I1f as a uniform single-domain response, while Section IV itself attributes the small current to cancellation by oppositely oriented domains. Without a domain-imbalance correction or an explicit lower-bound interpretation, the quoted γ1,13 values are not established as material constants.

major comments (4)
  1. [Section IV, Eq. (1)] The derivation of γ1,13 assumes I1f = fD²π²⟨ΔP⟩, with ⟨ΔP⟩ being the uniform single-domain polarization change. However, in the same section the paper states that the current can be low because 'the oppositely oriented polarizations cancel each other' and that the crossover I2f > I1f at Δφ > 4 mrad indicates such cancellation. Under that interpretation, I1f is proportional to the net polarization imbalance, not to the intrinsic single-domain response, and Eq. (1) yields an apparent value scaled by the inverse imbalance. The quoted γ1,13 ≈ 0.5 µC/N and ≈0.8 µC/N are therefore lower bounds at best; if triboelectric or ionic artifacts contribute, they are upper bounds. The manuscript must either measure or bound the domain imbalance (e.g., using the simultaneously recorded I2f, poling, or domain-area analysis) and correct the values, or explicitly present them as apparent lower-bound estima
  2. [Section IV, RM734 calculation] The text reads 'for RM734 at 128 °C in the NF phase where I1f = 10 nA'. This conflicts with Section III and Fig. 2(a), which place the 10 nA peak approximately 1.5 °C below the N–NF transition (≈131.5 °C), while at 128 °C the current is about 6 nA (rising to ≈6 nA at ≈127 °C). Recomputing Eq. (1) with I1f = 6 nA gives γ1,13 ≈ 0.3 µC/N, a 40% difference. The authors should state the exact temperature and current used and reconcile this with the temperature scan.
  3. [Section II, electrical connection] The induced current is measured through a gold sliding spring contact on the moving upper plate. A sliding metallic contact can generate triboelectric or contact-resistance noise at the mechanical frequency, and the reported nA-level signals are comparable to such artifacts. No blank measurement (empty cell) or control with a nonpiezoelectric fluid of similar viscosity is presented. Such controls are needed to rule out or bound the contact contribution to I1f.
  4. [Throughout Results] No error bars, confidence intervals, or replicate statistics are provided for I1f, I2f, |η*|, or the derived γ1,13. For a claimed quantitative material constant, uncertainty estimates are necessary. This is especially important for the DIO value, which relies on a single peak value at a strongly temperature-dependent phase transition.
minor comments (4)
  1. [Section II, Eq. (1)] The notation I1f(t) = I1f·sin(2πft + ψ1f) uses the same symbol for the time-dependent signal and its amplitude; a distinct symbol, e.g., I1f^0, would avoid confusion.
  2. [Section IV, Fig. 7] The complex viscosity data are described as measured at f = 10 Hz, but the strain amplitude used is not stated. Please specify whether the rheology measurements were performed at the same Δφ = 1 mrad used for the current measurements, since |η*| may depend on strain.
  3. [Section IV, comparison] The comparison with converse piezoelectric values is made against a different material (KPA-02) and at different frequencies. This should be explicitly caveated, since material differences and frequency dispersion are conflated.
  4. [Section IV, optical estimate] The estimate ξΔθ − ξ0 ≈ 8·10⁻² % at Δθ = 3 mrad is compared to a measured ~0.1% modulation at Δφ ≥ 4 mrad. Clarify whether the measured modulation is at Δφ = 4 mrad or 20 mrad, as the text is ambiguous.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the direct piezoelectric constants are obtained by applying the constitutive definition to measured current and measured complex viscosity.

full rationale

Walked the derivation chain. Eq. (1) is a direct rearrangement of the defining relation ΔP1 = γ1,13 T13 = γ1,13 S13 G, with measured I1f entering through I1f = f D^2 π^2 <ΔP> and measured |η*| entering through |G*| = 2π f |η*|. There is no fitted parameter being relabeled as a prediction, and no step in which an input is defined in terms of the output. The quoted γ1,13 values (RM734 and DIO) are simply the measured current divided by the measured rheological stress times geometric factors, so the conversion is definitional in the legitimate sense of a measurement. The theoretical-maximum current estimate uses only literature spontaneous polarization P and an assumed Δθ=6°, not the measured I1f. The paper's later statement that 'the oppositely oriented polarizations cancel each other' (Section IV) qualifies the physical interpretation: the extracted value would be a net/effective value if domains are unbalanced, but this is an accuracy limitation, not circularity. Self-citations [16,18,30] supply prior converse data, symmetry discussion, and rheological flow-alignment context; none is invoked as an unverified premise that forces the numerical result. The central claim is self-contained against directly measured input quantities.

Assumptions & free parameters 2 free parameters · 5 assumptions · 0 invented entities

The central extraction (Eq. 1) uses no fitted parameters: γ1,13 is computed from measured I1f, measured |η*|, and fixed geometry. The two listed free parameters enter only the speculative theoretical-maximum estimate. The axioms are standard constitutive/symmetry inputs from prior literature, except the implicit assumption that the measured current is purely piezoelectric, which is flagged.

free parameters (2)
  • Flow-alignment tilt angle Δθ = 6° (assumed)
    Typical nematic flow-alignment angle assumed for the maximum-current estimate (I_max ≈ 0.3 mA at 10 Hz); does not enter Eq. (1).
  • Spontaneous polarization magnitude P = 5×10⁻² C/m² (literature)
    Literature value for NF fluids used in the extreme-case current bound; not independently measured here and not used in the γ values.
assumptions (5)
  • domain assumption NF phase has C∞v symmetry, implying nonzero piezoelectric elements γ3,33, γ3,11(=γ3,22), γ1,13 and zero elements with odd counts of in-plane indices
    Invoked in Section IV to select γ1,13 as the measured component; from the review by the same group (ref [18]).
  • domain assumption Linear constitutive relation ΔP1 = γ1,13 T13 holds under the periodic strain; the rim strain at Δϕ = 1 mrad is 15.6% yet remains in the linear regime
    Used to derive Eq. (1) in Section IV; current-vs-Δϕ linearity is shown only up to Δϕ ≈ 2 mrad (Fig. 3b), so linearity at the full 15.6% rim strain is an extrapolation.
  • domain assumption Polarization is tangential to the local flow direction (axis 3 along flow)
    From ref [28] (same group); needed so the measured component is γ1,13 and not a mixture of tensor elements.
  • standard math Parallel-plate torsional kinematics: velocity field linear in gap, average strain <S> = (2/3)S_D/2
    Standard torsional-rheometry result (Mezger, ref [29]), used inside Eq. (1).
  • domain assumption Measured first-harmonic current is entirely due to piezoelectric polarization change, with no ionic streaming, electrokinetic, or sliding-contact contributions
    Implicit in Sections III–IV; no control experiment (empty cell or non-polar fluid) is reported.

how reviews work

0 comments
Cite this review

Pith. "Pith review of Shear-mode Direct Piezoelectric Response of Ferroelectric Nematic Liquid Crystals." pith.science (2026). https://pith.science/paper/IVUZWW2V

@misc{pith2026260723297,
  author       = {Pith},
  title        = {Pith review of: Shear-mode Direct Piezoelectric Response of Ferroelectric Nematic Liquid Crystals},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/IVUZWW2V}},
  note         = {Machine review of arXiv:2607.23297}
}
read the original abstract

Piezoelectricity (linear coupling between mechanical deformation and electric signal) was originally observed only in solid crystals. Recently, it was discovered that liquid ferroelectric nematic liquid crystals are also piezoelectric. However, so far only their converse piezoelectric signals (applied voltage-induced mechanical deformation) were measured quantitatively. In this work, we have carried out periodic shear-induced electric current and oscillatory rheology measurements on the two archetypic ferroelectric nematic compounds, RM734 and DIO. From temperature, frequency and strain dependent results of the first and second harmonic current signals together with the results from oscillatory rheometry, we were able to quantitatively determine the shear-mode direct piezoelectric coupling constants. These values are similar for both materials and are compared to results of previous converse piezoelectric measurements. We propose a physical mechanism in which the flow alignment of ferroelectric polarization leads to the direct piezoelectric response.

Discussion (0). Sign in to comment.

Reference graph

Works this paper leans on

34 extracted references · 2 canonical work pages

  1. [1]

    S. T. Lagerwall, Ferroelectric and Antiferroelectric Liquid Crystals, Wiley, 1999

    1999

  2. [2]

    R. J. Mandle, S. J. Cowling, J. W. Goodby, Physical Chemistry Chemical Physics 2017, 19, 11429

    2017

  3. [3]

    Nishikawa, K

    H. Nishikawa, K. Shiroshita, H. Higuchi, Y . Okumura, Y . Haseba, S. Yamamoto, K. Sago, H. Kikuchi, Advanced Materials 2017, 29, 1702354

    2017

  4. [4]

    Sebastián, M

    N. Sebastián, M. Čopič, A. Mertelj, Phys. Rev. E 2022, 106, 21001. 18

    2022

  5. [5]

    R. J. Mandle, N. Sebastián, J. Martinez -Perdiguero, A. Mertelj, Nat. Commun. 2021, 12, 4962

    2021

  6. [6]

    Sebastián, L

    N. Sebastián, L. Cmok, R. J. Mandle, M. R. De La Fuente, I. Drevenšek Olenik, M. Čopič, A. Mertelj, Phys. Rev. Lett. 2020, 124, 037801

    2020

  7. [7]

    Mertelj, L

    A. Mertelj, L. Cmok, N. Sebastián, R. J. Mandle, R. R. Parker, A. C. Whitwood, J. W. Goodby, M. Čopič, Phys. Rev. X 2018, 8, 041025

    2018

  8. [8]

    X. Chen, E. Korblova, D. Dong, X. Wei, R. Shao, L. Radzihovsky, M. A. Glaser, J. E. Maclennan, D. Bedrov, D. M. Walba, N. A. Clark, Proceedings of the National Academy of Sciences 2020, 117, 14021

    2020

Show all 34 references
  1. [9]

    M. T. Máthé, H. Nishikawa, F. Araoka, A. Jákli, P. Salamon, Nat. Commun. 2024, 15, 6928

    2024

  2. [10]

    Jarosik, H

    A. Jarosik, H. Nádasi, M. Schwidder, A. Manabe, M. Bremer, M. Klasen -Memmer, A. Eremin, Proceedings of the National Academy of Sciences 2024, 121, e2313629121

    2024

  3. [11]

    M. T. Máthé, K. Perera, Á. Buka, P. Salamon, A. Jákli, Advanced Science 2024, 11, 2305950

    2024

  4. [12]

    R. B. Meyer, Molecular Crystals and Liquid Crystals 1977, 40, 33

    1977

  5. [13]

    R. B. Meyer, L. Liebert, L. Strzelecki, P. Keller, Journal de Physique Lettres 1975, 36, 69

    1975

  6. [14]

    Niori, T

    T. Niori, T. Sekine, J. Watanabe, T. Furukawa, H. Takezoe, J. Mater. Chem. 1996, 6, 1231

    1996

  7. [15]

    H. Bock, W. Helfrich, Liq. Cryst. 1992, 12, 697

    1992

  8. [16]

    M. T. Máthé, M. S. H. Himel, A. Adaka, J. T. Gleeson, S. Sprunt, P. Salamon, A. Jákli, Adv. Funct. Mater. 2024, 34, 2314158

    2024

  9. [17]

    Medle Rupnik, L

    P. Medle Rupnik, L. Cmok, N. Sebastián, A. Mertelj, Adv. Funct. Mater. 2024, 34, DOI 10.1002/adfm.202402554

    2024 doi

  10. [18]

    M. Gill, M. T. Máthé, P. Salamon, J. T. Gleeson, A. Jákli, Mater. Horiz. 2025, 12, 8920

    2025

  11. [19]

    Paajanen, J

    M. Paajanen, J. Lekkala, K. Kirjavainen, Sens. Actuators A Phys. 2000, 84, 95

    2000

  12. [20]

    G. M. Sessler, J. Hillenbrand, Appl. Phys. Lett. 1999, 75, 3405

    1999

  13. [21]

    Zhang, G

    X. Zhang, G. M. Sessler, J. Hillenbrand, J. Electrostat. 2007, 65, 94. 19

    2007

  14. [22]

    Bauer, R

    S. Bauer, R. Gerhard-Multhaupt, G. M. Sessler, Phys. Today 2004, 57, 37

    2004

  15. [23]

    X. Chen, V . Martinez, E. Korblova, G. Freychet, M. Zhernenkov, M. A. Glaser, C. Wang, C. Zhu, L. Radzihovsky, J. E. Maclennan, D. M. Walba, N. A. Clark, Proceedings of the National Academy of Sciences 2023, 120, e2217150120

    2023

  16. [24]

    Medle Rupnik, E

    P. Medle Rupnik, E. Hanžel, M. Lovšin, N. Osterman, C. J. Gibb, R. J. Mandle, N. Sebastián, A. Mertelj, Advanced Science 2025, 12, DOI 10.1002/advs.202414818

    2025 doi

  17. [25]

    Thoen, G

    J. Thoen, G. Cordoyiannis, E. Korblova, D. M. Walba, N. A. Clark, W. Jiang, G. H. Mehl, C. Glorieux, Phys. Rev. E 2024, 110, 014703

    2024

  18. [26]

    Zhong, M

    B. Zhong, M. Shuai, X. Chen, V . Martinez, E. Korblova, M. A. Glaser, J. E. Maclennan, D. M. Walba, N. A. Clark, Soft Matter 2025, 21, 1122

    2025

  19. [27]

    Z. Ma, M. Jiang, A. Sun, S. Yi, J. Yang, M. Huang, S. Aya, Q.-H. Wei, Phys. Rev. Lett. 2025, 134, 238101

    2025

  20. [28]

    M. T. Máthé, Á. Buka, A. Jákli, P. Salamon, Phys. Rev. E 2022, 105, L052701

    2022

  21. [29]

    T. G. Mezger, The Rheology Handbook : For Users of Rotational and Oscillatory Rheometers, Vincentz Network, Hanover, 2020

    2020

  22. [30]

    Nishikawa, P

    H. Nishikawa, P. Salamon, M. T. Máthé, A. Jákli, F. Araoka, Giant 2025, 22, 100356

    2025

  23. [31]

    A. C. Das, S. Paladugu, O. D. Lavrentovich, Soft Matter 2026, DOI 10.1039/D5SM01207D

    2026 doi

  24. [32]

    C. L. Folcia, J. Ortega, R. Vidal, T. Sierra, J. Etxebarria, Liq. Cryst. 2022, 49, 899

    2022

  25. [33]

    Lovšin, L

    M. Lovšin, L. Cmok, C. J. Gibb, J. Hobbs, R. J. Mandle, A. Mertelj, I. Drevenšek‐Olenik, N. Sebastián, Adv. Opt. Mater. 2026, 14, e03018

    2026

  26. [34]

    R. Xia, X. Zhao, J. Li, H. Lei, Y . Song, W. Peng, X. Zhang, S. Aya, M. Huang, J. Mater. Chem. C Mater. 2023, 11, 10905

    2023

Pith tools

Reviewed July 31, 2026 · model on record in the stance chip above.