Fluctuation-induced dynamics of nematic topological defects

Bonn, Lasse; Ardaševa, Aleksandra; Mueller, Romain; Shendruk, Tyler N.; Doostmohammadi, Amin

doi:10.1103/physreve.106.044706

Cited by 5 publications

(8 citation statements)

References 114 publications

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“…It is also noteworthy that this flipping of the stress also corresponds to the switch between extensile and contractile behavior of topological defects in active nematics. 20 Experimental evidence of such a switch is presented in epithelial layers upon weakening of cell–cell adhesion, 49 and while various active mechanisms have been proposed for the flipping of extensile-contractile defect behavior, 25,50 these results show that such a flipping can simply occur upon changing of the oreintational elasticity of the nematogens, a passive material property.…”

Section: Resultsmentioning

confidence: 99%

“…A simple explanation is that while the in an active nematic the stress dipole is dominated by activity, 48 the stress localization for the fluctuation induced defect is controlled by elastic effects. 25 As the elastic constant, K , increases, the strength of elastic effects is increased until they overcome the active effects, and the stress dipole flips direction from compression → tension dipole to tension → compression along the tail → head direction around the comet-like +1/2 defect. This switch in the tension–compression regions by only changing the elastic constant presents an interesting, simple, way for switching the dynamic behavior in active matter by changing a passive material property.…”

Section: Resultsmentioning

confidence: 99%

“…We implement fluctuating two-dimensional nematohydrodynamics as described in ref. 25. The equations are implemented with a hybrid lattice-Boltzmann approach.…”

Section: Methodsmentioning

confidence: 99%

“…It has been shown that breaking detailed balance by fluctuations of different kinds, such as fluctuations in the order parameter field, velocity field or angle of the director, can lead to very similar defect dynamics as observed with active stresses. 25…”

Section: Methodsmentioning

confidence: 99%

“…Therefore, to break detailed balance without including active stresses, we include fluctuations in the angle of the nematic. At every step we calculate the angle θ l of the director at lattice point l , and add a random angle, taken from the uniform distribution U , scaled by the fluctuation strength ξ θ : 25 and then reconstruct Q ij . This method preserves the symmetry and tracelessness of the order parameter, changing only the effective angle.…”

Section: Methodsmentioning

confidence: 99%

See 4 more Smart Citations

Elasticity tunes mechanical stress localization around active topological defects

Bonn,

Ardaševa,

Doostmohammadi

2024

Soft Matter

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

“…We implement fluctuating two-dimensional nematohydrodynamics as described in ref. 25. The equations are implemented with a hybrid lattice-Boltzmann approach.…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 3 more Smart Citations

Elasticity tunes mechanical stress localization around active topological defects

Bonn,

Ardaševa,

Doostmohammadi

2024

Soft Matter

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Fourier-space Monte Carlo simulations of two-dimensional nematic liquid crystals

Tang,

Chen,

Zhang

2024

The Journal of Chemical Physics

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Thermal fluctuations are ubiquitous in mesoscopic and microscopic systems. Take nematic liquid crystals (LCs) as an example; their director fluctuations can strongly scatter light and give rise to random motions and rotations of topological defects and solid inclusions. These stochastic processes contain important information about the material properties of the LC and dictate the transport of the immersed colloidal particles. However, modeling thermal fluctuations of the nematic field remains challenging. Here, we introduce a new Monte Carlo simulation method, namely the Fourier-space Monte Carlo (FSMC) method, which is based on the Oseen–Frank elastic distortion energy model. This method accurately models the thermal fluctuations of a nematic LC’s director field. In contrast to the traditional real-space MC method, which perturbs the director locally, the FSMC method samples different eigenmodes of the director distortions in the Fourier space, aligning with the equipartition theorem. We apply FSMC to study defect fluctuations and trajectories in a two-dimensional nematic LC confined to various geometries. Our results show that FSMC can effectively sample degenerate defect configurations and reproduce long-range elastic interactions between defects. In addition, we conduct three-dimensional molecular dynamics simulations using a coarse-grained Gay–Berne potential, which corroborates the findings from FSMC. Taken together, we have developed a new Monte Carlo method to accurately model thermal fluctuations in nematic LCs, which can be useful for searching global free-energy minimum states in nematic, smectic, and other LC mesophases and can also be helpful in modeling the thermal motions of defects and inclusions in LCs.

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Active topological defect absorption by a curvature singularity

Vafa

Nelson

Doostmohammadi³

2023

J. Phys.: Condens. Matter

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We leverage the Born-Oppenheimer approximation to present a general description of topological defects dynamics in $p$-atic materials on curved surfaces. Focusing on the case of an active nematic, we find that activity induces a geometric contribution to the motility of the $+1/2$ defect. Moreover, in the case of a cone, the simplest example of a geometry with curvature singularity, we find that the motility depends on the deficit angle of the cone and changes sign when the deficit angle is bigger than $\pi$, leading to the change in active behavior from contractile (extensile) to extensile (contractile) behavior. Using our analytical framework, we then identify for positively charged defects the basin of attraction to the cone apex and present closed-form predictions for defect trajectories near the apex. The analytical results are quantitatively corroborated against full numerical simulations, with excellent agreement when the capture radius is small compared to the cone size.

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Fluctuation-induced dynamics of nematic topological defects

Cited by 5 publications

References 114 publications

Elasticity tunes mechanical stress localization around active topological defects

Elasticity tunes mechanical stress localization around active topological defects

Fourier-space Monte Carlo simulations of two-dimensional nematic liquid crystals

Active topological defect absorption by a curvature singularity

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