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arxiv: 2606.21231 · v1 · pith:IBNP363Wnew · submitted 2026-06-19 · ❄️ cond-mat.soft

Exotic topological defects and director fields in free-floating spherical ferroelectric nematic liquid crystal shells

Pith reviewed 2026-06-26 12:50 UTC · model grok-4.3

classification ❄️ cond-mat.soft
keywords ferroelectric nematicspherical shellstopological defectsdirector fieldbend-twist defectssecond-harmonic generationantiferroelectric phase
0
0 comments X

The pith

Ferroelectric nematic shells develop azimuthal director fields around two antipodal +1 bend-twist defects.

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

The paper studies ferroelectric nematic liquid crystals in free-floating spherical shells with tangential boundaries that require a total defect charge of +2. It establishes that in the NF phase these shells form an azimuthal director field around two antipodal +1 bend-twist defects rather than the splayed half-integer defects seen in ordinary nematics. Second-harmonic generation microscopy verifies the non-centrosymmetric azimuthal setup. The antiferroelectric phase shows zigzag lines while the high-temperature nematic phase shows four +1/2 disclinations near thin spots. This reveals how polar order changes topological defect arrangements in curved confinement.

Core claim

In the ferroelectric nematic phase our thin RM734+DIO shells with inner and outer aqueous poly(vinyl alcohol) solutions develop an azimuthal director field around two antipodal +1 bend-twist defects. The non-centrosymmetric nature and the azimuthal director configuration of the shells in the NF phase are confirmed also through second-harmonic generation microscopy.

What carries the argument

Two antipodal escaped +1 bend-twist defects that carry the total +2 topological charge in polar ferroelectric nematic shells.

If this is right

  • The polar symmetry leads to avoidance of splayed half-integer defects in favor of bend-twist +1 defects.
  • The antiferroelectric Nx phase generates zigzag line textures in the shells.
  • In the regular N phase the shells show the usual four +1/2 disclinations near the thinnest points.
  • Spherical shells serve as a platform to explore exotic liquid crystals under topological constraints.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • This configuration may enable controlled polarization responses in spherical geometries for sensing or actuation.
  • Tuning temperature could switch defect textures for adaptive materials.
  • The preference for bend-twist defects might appear in other confined polar media beyond liquid crystals.

Load-bearing premise

The boundary conditions stay purely tangential and the director field is controlled by the bulk properties of the NF phase.

What would settle it

Direct observation of splayed half-integer defects in the NF phase shells would show the claim is incorrect.

read the original abstract

Ferroelectric nematic (NF) liquid crystals exhibit polar symmetry and large polarization, giving rise to phenomena absent in conventional apolar nematics. We investigate NF liquid crystals confined to free-floating spherical shells with tangential boundary conditions, enforcing a total topological defect charge of +2. We conjecture that ferroelectric nematics avoid splayed configurations with half-integer defects, common in apolar nematic shells, instead concentrating the topological charge into escaped azimuthal +1 defects requiring only bend and twist. Indeed, at room temperature in the NF phase, our thin RM734+DIO shells with inner and outer aqueous poly(vinyl alcohol) solutions develop an azimuthal director field around two antipodal +1 bend-twist defects. The non-centrosymmetric nature and the azimuthal director configuration of the shells in the NF phase are confirmed also through second-harmonic generation microscopy. At intermediate temperature the antiferroelectric Nx phase generates a new exotic texture rife in zigzag lines in the shells. In the regular N phase at high temperature, the shells develop the usual four +1/2 disclinations located near the thinnest point. Our study highlights the rich platform offered by spherical shells to study the behavior of exotic liquid crystals subject to topological constraints, possibly opening new paths to apply the highly responsive ferroelectric nematic phase

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript reports experimental observations of director fields and topological defects in free-floating spherical shells of the ferroelectric nematic liquid crystal RM734+DIO under tangential boundary conditions enforced by aqueous PVA solutions. In the NF phase at room temperature, the shells exhibit an azimuthal director configuration with two antipodal +1 bend-twist defects; this is contrasted with four +1/2 disclinations in the high-temperature N phase and a zigzag texture in the intermediate Nx phase. The non-centrosymmetric azimuthal structure in the NF phase is additionally confirmed via second-harmonic generation (SHG) microscopy. The central conjecture is that the polar symmetry of the NF phase favors escaped +1 defects (bend-twist only) over the splayed half-integer defects typical of apolar nematics.

Significance. If the reported phase-specific defect configurations hold, the work demonstrates how the spontaneous polarization and non-centrosymmetric order of the NF phase qualitatively alter topological defect selection under spherical confinement, providing a new experimental platform for polar nematics. The direct optical and SHG observations constitute a clear experimental strength; the temperature-dependent switching between configurations further supports the assignment to distinct phases.

major comments (2)
  1. [Abstract and experimental description] The central claim that the observed azimuthal +1 defects are determined by bulk NF properties rather than shell-thickness variations or specific PVA interactions rests on the assumption of purely tangential anchoring without polar bias. The manuscript does not provide quantitative evidence (e.g., anchoring energy measurements or thickness maps correlated with defect positions) that rules out thickness-driven artifacts or weak polar contributions from the PVA solutions; this is load-bearing for interpreting the configuration as intrinsic to the NF phase.
  2. [SHG microscopy results] While SHG microscopy is used to confirm the non-centrosymmetric azimuthal director field, the manuscript does not report the polarization dependence, intensity calibration, or control measurements (e.g., on the N phase) needed to quantitatively distinguish the azimuthal configuration from possible escaped radial or other polar arrangements; this weakens the strength of the SHG confirmation for the specific defect topology.
minor comments (2)
  1. [Methods] The description of shell preparation (inner/outer PVA concentrations, shell thickness range) should be expanded with specific values and variability statistics to allow reproducibility.
  2. [Figure captions] Figure captions and text should explicitly label the temperature ranges corresponding to each phase (NF, Nx, N) for the presented micrographs.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the positive evaluation and constructive major comments. We respond to each point below, indicating where the manuscript will be revised for clarity while maintaining that the phase-specific observations support our central interpretation.

read point-by-point responses
  1. Referee: [Abstract and experimental description] The central claim that the observed azimuthal +1 defects are determined by bulk NF properties rather than shell-thickness variations or specific PVA interactions rests on the assumption of purely tangential anchoring without polar bias. The manuscript does not provide quantitative evidence (e.g., anchoring energy measurements or thickness maps correlated with defect positions) that rules out thickness-driven artifacts or weak polar contributions from the PVA solutions; this is load-bearing for interpreting the configuration as intrinsic to the NF phase.

    Authors: We agree that direct anchoring energy measurements and correlated thickness maps are absent and would strengthen the manuscript. However, the defect configurations switch reproducibly with temperature in lockstep with the known bulk phases of RM734+DIO (azimuthal +1 in NF, zigzag in Nx, four +1/2 in N), which would be difficult to explain if thickness or PVA polar bias were dominant. Standard PVA solutions are widely used for tangential anchoring in nematic shells without inducing polar bias in the apolar N phase. We will add a paragraph in the discussion explicitly addressing possible boundary effects and the phase-specific evidence against thickness-driven selection. revision: partial

  2. Referee: [SHG microscopy results] While SHG microscopy is used to confirm the non-centrosymmetric azimuthal director field, the manuscript does not report the polarization dependence, intensity calibration, or control measurements (e.g., on the N phase) needed to quantitatively distinguish the azimuthal configuration from possible escaped radial or other polar arrangements; this weakens the strength of the SHG confirmation for the specific defect topology.

    Authors: The SHG data serve primarily to confirm the non-centrosymmetric character of the NF phase, with the specific azimuthal director field and defect topology established by polarized optical microscopy textures. Polarization-resolved SHG and N-phase controls were not performed. We will revise the methods and results sections to include a more detailed description of the SHG geometry and any available intensity information, while clarifying the complementary roles of the two techniques. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental observations only

full rationale

This is an experimental paper reporting direct optical and SHG microscopy observations of director configurations and defects in NF, Nx, and N phases of liquid crystal shells. No mathematical derivation, fitted parameters, or predictions are presented that could reduce to inputs by construction. The conjecture about avoiding splayed half-integer defects is stated as such and is not used as a load-bearing step in any equation chain. Boundary conditions are discussed via standard PVA use but are not derived from the paper's own results. All claims rest on independent experimental data rather than self-referential fitting or citation chains.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The paper is experimental; no free parameters are fitted to data in a derivation sense. It relies on the standard topological result that a sphere with tangential director field requires total defect charge +2.

axioms (1)
  • standard math A sphere with tangential director boundary conditions requires total topological defect charge of +2
    Invoked in the first paragraph to set the defect constraint for all shells.

pith-pipeline@v0.9.1-grok · 5798 in / 1394 out tokens · 30552 ms · 2026-06-26T12:50:10.370409+00:00 · methodology

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Reference graph

Works this paper leans on

41 extracted references · 17 canonical work pages

  1. [1]

    Col- loid and Polymer Science289(4), 345–359 (2011) https://doi.org/10.1007/ s00396-010-2367-7

    Lopez-Leon, T., Fernandez-Nieves, A.: Drops and shells of liquid crystal. Col- loid and Polymer Science289(4), 345–359 (2011) https://doi.org/10.1007/ s00396-010-2367-7 . March 5, 2011. Record 102 of 146

  2. [2]

    Nature Physics7, 391–394 (2011)

    Lopez-Leon, T., Koning, V., Devaiah, K.B.S., Vitelli, V., Fernandez-Nieves, A.: Frustrated nematic order in spherical geometries. Nature Physics7, 391–394 (2011)

  3. [3]

    Journal of Physics: Condensed Matter29(13), 133003 (2017)

    Urbanski, M., Reyes, C.G., Noh, J., Sharma, A., Geng, Y., Jampani, V.S.R., Lagerwall, J.P.F.: Liquid crystals in micron-scale droplets, shells and fibers. Journal of Physics: Condensed Matter29(13), 133003 (2017)

  4. [4]

    Physical Review E79(2), 021707 (2009)

    Lopez-Leon, T., Fernandez-Nieves, A.: Topological transformations in bipolar shells of nematic liquid crystals. Physical Review E79(2), 021707 (2009)

  5. [5]

    Soft Matter12(2), 367–372 (2016) https://doi.org/10.1039/C5SM01944C

    Noh, J., Sousa, K., Lagerwall, J.P.F.: Influence of interface stabilisers and sur- rounding aqueous phases on nematic liquid crystal shells. Soft Matter12(2), 367–372 (2016) https://doi.org/10.1039/C5SM01944C

  6. [6]

    Physical Review Research2(3), 033160 (2020)

    Noh, J., Wang, Y., Liang, H.-L., Jampani, V.S.R., Majumdar, A., Lagerwall, J.P.F.: Dynamic tuning of the director field in liquid crystal shells using block copolymers. Physical Review Research2(3), 033160 (2020)

  7. [7]

    Langmuir35(34), 11132–11140 (2019) https://doi.org/10.1021/acs.langmuir.9b00989

    Sharma, A., Jampani, V.S.R., Lagerwall, J.P.F.: Realignment of liquid crystal shells driven by temperature-dependent surfactant solubility. Langmuir35(34), 11132–11140 (2019) https://doi.org/10.1021/acs.langmuir.9b00989

  8. [8]

    Nat Commun15(1), 1404 (2024)

    Ma, X., Han, Y., Zhang, Y., Geng, Y., Majumdar, A., Lagerwall, J.: Tunable templating of photonic microparticles via liquid crystal order-guided adsorption of amphiphilic polymers in emulsions. Nat Commun15(1), 1404 (2024)

  9. [9]

    Proc Natl Acad Sci U S A117(25), 14021– 14031 (2020)

    Chen, X., Korblova, E., Dong, D., Wei, X., Shao, R., Radzihovsky, L., Glaser, M., Maclennan, J., Bedrov, D., Walba, D., Clark, N.: First-principles experimental demonstration of ferroelectricity in a thermotropic nematic liquid crystal: Polar domains and striking electro-optics. Proc Natl Acad Sci U S A117(25), 14021– 14031 (2020)

  10. [10]

    Proceedings of the National Academy of Sciences117(24), 14021–14029 (2020) https://doi.org/10.1073/pnas.2002290117

    Mandle, R.J.e.a.: First-principles experimental demonstration of ferroelectricity in a thermotropic nematic liquid crystal: Polar domains and striking electro- optics. Proceedings of the National Academy of Sciences117(24), 14021–14029 (2020) https://doi.org/10.1073/pnas.2002290117

  11. [11]

    Proceedings of the National Academy of Sciences118(22), 2104092118 (2021) 14 https://doi.org/10.1073/pnas.2104092118

    Lavrentovich, O.D.e.a.: Polar in-plane surface orientation of a ferroelectric nematic liquid crystal: Polar monodomains and twisted state electro-optics. Proceedings of the National Academy of Sciences118(22), 2104092118 (2021) 14 https://doi.org/10.1073/pnas.2104092118

  12. [12]

    Nature Communications14(1), 3029 (2023) https://doi.org/10

    Sebasti´ an, N., Lovˇ sin, M., Berteloot, B., Bregar, N., Challa, P.K., Lin, X., S´ anchez-Ferrer, A., D¨ ur´ an, J.D., Mertelj, A., Osipov, M.A., Lavrentovich, O.D., Museviˇ c, I.: Polarization patterning in ferroelectric nematic liquids via flexoelec- tric coupling. Nature Communications14(1), 3029 (2023) https://doi.org/10. 1038/s41467-023-38749-2

  13. [13]

    Nature Communications16(1), 55827 (2025) https://doi

    Basnet, B., Paladugu, S.R., Sebastian, N., Bregar, N., Lavrentovich, O.D., Mertelj, A., Museviˇ c, I., Harth, K.: Periodic splay fr´ eedericksz transitions in a ferroelectric nematic. Nature Communications16(1), 55827 (2025) https://doi. org/10.1038/s41467-025-55827-9

  14. [14]

    Nature Communications16(1), 6516 (2025) https://doi.org/10.1038/ s41467-025-61840-9

    Lavrentovich, M.O., Kumari, P., Li, C.-Y., Li, Y., Li, L., Lavrentovich, O.D.: Twist, splay, and uniform domains in ferroelectric nematic liquid crystals. Nature Communications16(1), 6516 (2025) https://doi.org/10.1038/ s41467-025-61840-9

  15. [15]

    Nature Communications16(1), 61840 (2025) https://doi.org/10

    Bennett, T.,et al.: Twist, splay, and uniform domains in ferroelectric nematic liquid crystals. Nature Communications16(1), 61840 (2025) https://doi.org/10. 1038/s41467-025-61840-9

  16. [16]

    Soft Matter21(38), 7508–7518 (2025) https: //doi.org/10.1039/D5SM00670H

    Zavvou, E., Ma, Z., Vaupotiˇ c, N., Caimi, R., Mertelj, A., Lavrentovich, O.D., ˇZumer, S.: Signatures of polar order in a ferroelectric nematic liquid crystal: splay stiffening and twist softening. Soft Matter21(38), 7508–7518 (2025) https: //doi.org/10.1039/D5SM00670H

  17. [17]

    Soft Matter19(3), 347–354 (2023) https://doi.org/10.1039/ d2sm01395a

    Perera, K., Saha, R., Nepal, P., Dharmarathna, R., Hossain, M.S., Mostafa, M., Adaka, A., Waroquet, R., Twieg, R.J., J´ akli, A.: Ferroelectric nematic droplets in their isotropic melt. Soft Matter19(3), 347–354 (2023) https://doi.org/10.1039/ d2sm01395a

  18. [18]

    Nature Communications (2022) https://doi.org/10.1038/ s41467-022-35443-7

    Yang, J., al.: Spontaneous electric-polarization topology in confined fer- roelectric nematics. Nature Communications (2022) https://doi.org/10.1038/ s41467-022-35443-7

  19. [19]

    Nature Communications (2026) https://doi.org/10.1038/s41467-026-73557-4

    Zou, Y., Yang, J., Ma, Z., Hong, Z., Sun, A., Huang, X., Deng, M., Huang, M., Wei, Q.-H., Aya, S.: Self-charged polar nematic monopoles and hybrid topologi- cal states: intertwining and domain integration. Nature Communications (2026) https://doi.org/10.1038/s41467-026-73557-4

  20. [20]

    Chemistry23(58), 14554–14562 (2017) https://doi.org/10.1002/chem.201702742

    Mandle, R.J., Cowling, S.J., Goodby, J.W.: Rational design of rod-like liquid crystals exhibiting two nematic phases. Chemistry23(58), 14554–14562 (2017) https://doi.org/10.1002/chem.201702742

  21. [21]

    15 Adv Mater29(43) (2017) https://doi.org/10.1002/adma.201702354

    Nishikawa, H., Shiroshita, K., Higuchi, H., Okumura, Y., Haseba, Y., Yamamoto, S.I., Sago, K., Kikuchi, H.: A fluid liquid-crystal material with highly polar order. 15 Adv Mater29(43) (2017) https://doi.org/10.1002/adma.201702354

  22. [22]

    7-10, 1526–1540,https://doi.org/10.1080/ 02678292.2022.2150790

    Chen, X., Zhu, Z., Magrini, M.J., Korblova, E., Park, C.S., Glaser, M.A., Clark, N.A.: Ideal mixing of paraelectric and ferroelectric nematic phases in liquid crystals of distinct molecular species. Liquid Crystals49(11), 1531–1544 (2022) https://doi.org/10.1080/02678292.2022.2058101

  23. [23]

    Soft Matter (2025) https://doi.org/10.1039/D5SM00796H

    Ghimire, A., Basnet, B., Wang, H., Guragain, P., Baldwin, A., Twieg, R., Lavren- tovich, O.D., Gleeson, J., Jakli, A., Sprunt, S.: Dynamics of the antiferroelectric smectic-ZA phase in a ferroelectric nematic liquid crystal. Soft Matter (2025) https://doi.org/10.1039/D5SM00796H

  24. [24]

    Advanced Materials29, 1702354 (2017) https://doi.org/10.1002/adma

    Nishikawa, H., al.: A fluid liquid-crystal material with highly polar order. Advanced Materials29, 1702354 (2017) https://doi.org/10.1002/adma. 201702354

  25. [25]

    Physical Review E106, 021001 (2022) https://doi.org/10.1103/PhysRevE.106.021001

    Sebasti´ an, N., al.: Ferroelectric nematic liquid-crystalline phases. Physical Review E106, 021001 (2022) https://doi.org/10.1103/PhysRevE.106.021001

  26. [26]

    Soft Matter20, 3392 (2024) https://doi.org/ 10.1039/d3sm01042b

    Zou, Y., al.: Topology of ferroelectric nematic droplets: the case driven by flex- oelectricity or depolarization field. Soft Matter20, 3392 (2024) https://doi.org/ 10.1039/d3sm01042b

  27. [27]

    Adv Mater34(5), 2107338 (2022)

    Wang, J., Hahn, S., Amstad, E., Vogel, N.: Tailored double emulsions made simple. Adv Mater34(5), 2107338 (2022)

  28. [28]

    the ouzo effect

    Vitale, S.A., Katz, J.L.: Liquid droplet dispersions formed by homogeneous liquid- liquid nucleation: “the ouzo effect”. Langmuir19(10), 4105–4110 (2003)

  29. [29]

    Colloids and Surfaces A: Physicochemical and Engineering Aspects 225(1-3), 153–160 (2003)

    Grillo, I.: Small-angle neutron scattering study of a world-wide known emulsion: Le pastis. Colloids and Surfaces A: Physicochemical and Engineering Aspects 225(1-3), 153–160 (2003)

  30. [30]

    Soft Matter19(14), 2637–2645 (2023)

    Sharma, A., Kizhakidathazhath, R., Lagerwall, J.: Impact of mesogenic aromatic- ity and cyano termination on the alignment and stability of liquid crystal shells. Soft Matter19(14), 2637–2645 (2023)

  31. [31]

    Haase, M.F., Brujic, J.: Tailoring of high-order multiple emulsions by the liquid- liquid phase separation of ternary mixtures. Angew. Chem.126(44), 11987–11991 (2014)

  32. [32]

    Physical Review Research4(1), 013130 (2022)

    Sharma, A., Gupta, D., Scalia, G., Lagerwall, J.P.F.: Lipid islands on liquid crystal shells. Physical Review Research4(1), 013130 (2022)

  33. [33]

    Journal de Physique33(5-6), 591–598 (1972)

    Cladis, P.E., Kl´ eman, M.: Non-singular disclinations of strength s = + 1 in nematics. Journal de Physique33(5-6), 591–598 (1972)

  34. [34]

    Yang, C., Chen, R., Feng, L., Zhang, R., Chen, D.: Electro-optic response of 16 bipolar nematic liquid crystal confined in oblate spheroid. Front. Soft. Matter2 (2022) https://doi.org/10.3389/frsfm.2022.1022077

  35. [35]

    Soft Matter (2024)

    Sharma, A., Magrini, M., Han, Y., Walba, D.M., Majumdar, A., Lagerwall, J.P.F.: How smectic-a and smectic-c liquid crystals resolve confinement-induced frustration in spherical shells. Soft Matter (2024)

  36. [36]

    Liquid Crystals49, 899 (2022)

    Folcia, C.L., Ortega, J., Vidal, R., Sierra, T., Etxebarria, J. Liquid Crystals49, 899 (2022)

  37. [37]

    Lovšin, L

    Lovˇ sin, M., al.: Ferroelectric fluids for nonlinear photonics: Evaluation of temper- ature dependence of second-order susceptibilities. Advanced Optical Materials, 03018 (2026) https://doi.org/10.1002/adom.202503018

  38. [38]

    Journal of Materials Chemistry C11, 10905 (2023)

    Xia, R., Zhao, X., Li, J., Lei, H., Song, Y., Peng, W., Zhang, X., Aya, S., Huang, M. Journal of Materials Chemistry C11, 10905 (2023)

  39. [39]

    Philosophical Magazine27(2), 405–424 (1973)

    Meyer, R.B.: On the existence of even indexed disclinations in nematic liquid crystals. Philosophical Magazine27(2), 405–424 (1973)

  40. [40]

    Advanced Optical Materials9(22), 2101230 (2021) https://doi.org/10.1002/ adom.202101230

    Feng, C., Saha, R., Korblova, E., Walba, D., Sprunt, S.N., J´ akli, A.: Elec- trically tunable reflection color of chiral ferroelectric nematic liquid crystals. Advanced Optical Materials9(22), 2101230 (2021) https://doi.org/10.1002/ adom.202101230 . Times cited: 15

  41. [41]

    −%&'"( O!

    Lagerwall, J.P.F.: Innovative applications enabled by the versatile structural color of cholesteric liquid crystals. Acc. Mater. Res.7(4), 319–329 (2026) https://doi. org/10.1021/accountsmr.5c00177 17 Supplementary Information S1 Materials The following materials are used for this study: • 4-[(4-nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (RM734). ...