Breaking planar liquid crystal anchoring to form controllable twist disclination loops

Angelo, Joseph; Culbreath, Christopher; Yokoyama, Hiroshi

doi:10.1080/15421406.2017.1287486

Cited by 3 publications

(1 citation statement)

References 6 publications

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“…Disclinations in nematics nucleate, move, and annihilate in response to elastic stress [9] and fluid flow [10,11]. In passive liquid crystals, disclinations form during cooling into the nematic phase, or when surface anchoring is broken [12], and may be stabilized by topological constraints such as those associated with colloidal inclusions [13] and patterned surface anchoring [14][15][16]. In active nematics, disclinations spontaneously nucleate, move, and annihilate [17][18][19][20][21][22][23].…”

Section: Introductionmentioning

confidence: 99%

Frank-Read Mechanism in Nematic Liquid Crystals

Cheng

Deutsch

Angelo

et al. 2023

Preprint

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In a crystalline solid under mechanical stress, a Frank-Read source is a pinned dislocation segment that repeatedly bows and detaches, generating concentric dislocation loops. We demonstrate that in nematic liquid crystals, an analogous Frank-Read mechanism generates concentric disclination loops. Using experiment, simulation, and theory, we study a disclination segment pinned between surface defects on one substrate in a nematic cell. Under applied twist of the nematic director, the pinned segment bows and emits a new disclination loop which expands, leaving the original segment intact; loop emission repeats for each additional 180 degrees of applied twist. We present experimental micrographs showing loop expansion and snap-off, numerical simulations of loop emission under both quasistatic and dynamic loading, and theoretical analysis considering both free energy minimization and the balance of competing forces. Lastly, we discuss potential use of Frank-Read sources to modify microstructural evolution in both passive and active nematics.

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Section: Introductionmentioning

confidence: 99%

Frank-Read Mechanism in Nematic Liquid Crystals

Cheng

Deutsch

Angelo

et al. 2023

Preprint

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Unknots, knots, links and necklaces made of dislocations in cholesterics

Pieranski,

Godinho

2024

Liquid Crystals

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We deal with the genesis and decay of knots and links made of dislocations in a cholesteric layer confined in the gap between orthogonal cylindrical mica sheets. The genesis starts by nucleation of folded unknots driven by a compressive strain. The nucleation process of the trivial and folded unknots is studied and discussed in detail. We show that the expansion of the folded unknots leads to their lateral collisions followed by the coalescence into the torus knots, such as the trefoil knot, or into the links, such as the Hopf and Solomon links. The viscoelastic decays of knots and links follow well defined pathes involving topological and geometrical transformations. In particular, the symmetric configuration of the Hopf link is unstable with respect to the shrinking of one of its interlaced loops. The final asymmetric configuration, made of a minimal loop tethered on a large cargo loop, is called the Hopf necklace. Similarly, the double Hopf necklace is obtained by the elastic decay of the Solomon link. We emphasize that Hopf necklaces of various orders are quite ubiquitous.

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Frank-Read Mechanism in Nematic Liquid Crystals

Long,

Deutsch,

Angelo

et al. 2024

Phys. Rev. X

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In a crystalline solid under mechanical stress, a Frank-Read source is a pinned dislocation segment that repeatedly bows and detaches, generating concentric dislocation loops. We demonstrate that, in nematic liquid crystals, an analogous Frank-Read mechanism can generate concentric disclination loops. Using experiment, simulation, and theory, we study a disclination segment pinned between surface defects on one substrate in a nematic cell. Under applied twist of the nematic director, the pinned segment bows and emits a new disclination loop which expands, leaving the original segment intact; loop emission repeats for each additional 180° of applied twist. We present experimental micrographs showing loop expansion and snap-off, numerical simulations of loop emission under both quasistatic and dynamic loading, and theoretical analysis considering both free energy minimization and the balance of competing forces. We find that the critical stress for disclination loop emission scales as the inverse of segment length and changes as a function of strain rate and temperature, in close analogy to the Frank-Read source mechanism in crystals. Lastly, we discuss how Frank-Read sources could be used to modify microstructural evolution in both passive and active nematics. Published by the American Physical Society 2024

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Breaking planar liquid crystal anchoring to form controllable twist disclination loops

Cited by 3 publications

References 6 publications

Frank-Read Mechanism in Nematic Liquid Crystals

Frank-Read Mechanism in Nematic Liquid Crystals

Unknots, knots, links and necklaces made of dislocations in cholesterics

Frank-Read Mechanism in Nematic Liquid Crystals

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