Competition of lattice and basis for alignment of nematic liquid crystals

DeBenedictis, Andrew; Atherton, Timothy J.; Anquetil-Deck, Candy; Cleaver, Douglas J.; Emerson, D. B.; Wolak, Mathew; Adler, James H.

doi:10.1103/physreve.92.042501

Cited by 6 publications

(3 citation statements)

References 56 publications

(59 reference statements)

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“…where β = 1/k B T and the z-axis has been chosen to be perpendicular to the substrates, located at z = z α 0 (α = 1, 2). According to equation (1), particles see each other as HGOs, but the substrates see a particle as an infinitely thin disc of diameter D (which need not be the same at both substrates, or in different regions of each substrate [38,39]). This is the oblate-particle version of the hard needle-wall potential of our earlier work [27][28][29][30]: physically, 0 < D < σ 0 means that the particles are able to embed their side-and end groups, but not the whole width of their cores, into the bounding walls.…”

Section: Theorymentioning

confidence: 99%

Ordering of oblate hard particles between symmetric penetrable walls

2020

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We find the structure of a model discotic liquid crystal (DLC) confined between symmetric walls of controllable penetrability. The model consists of oblate hard Gaussian overlap (HGO) particles.Particle-substrate interactions are modelled as follows: each substrate sees a particle as a disc of zero thickness and diameter D less than or equal to that of the actual particle, σ 0 , embedded inside the particle and located halfway along, and perpendicular to, its minor axis. This allows us to control the anchoring properties of the substrates, from planar (edge-on) for D ∼ 0 to homeotropic (face-on) for D ∼ σ 0 . This system is investigated using both Monte Carlo simulation and densityfunctional theory, the latter implemented at the level of Onsager's second-virial approximation with Parsons-Lee rescaling. We find that the agreement between theory and simulation is substantially less good than for prolate HGOs; in particular, the crossover from edge-on to face-on alignment is predicted by theory to occur at D ∼ 0.65σ 0 , but simulation finds it for D ∼ 0.55σ 0 . These discrepancies are likely a consequence of the fact that Onsager's theory is less accurate for discs than for rods. We quantify this by computing the bulk isotropic-nematic phase diagram of oblate HGOs.

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Section: Theorymentioning

confidence: 99%

Ordering of oblate hard particles between symmetric penetrable walls

2020

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“…If the center-to-center distance d ij is smaller than the contact distance σ ij , there is overlap. This criterion has been successfully implemented in other work [55][56][57][58]. If two ellipsoidal particles overlap, we exert the Gaussian model potential [59] V (u i , u j , d ij ) = 0 1 − χ 2 ( ûi…”

Section: Packing Algorithm For Ellipsoidal Particlesmentioning

confidence: 99%

Elongation and percolation of defect motifs in anisotropic packing problems

Xie

Atherton

2020

Preprint

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We examine the regime between crystalline and amorphous packings of anisotropic objects on surfaces of different genus by continuously varying their size distribution or shape from monodispersed spheres to bidispersed mixtures or monodispersed ellipsoidal particles; we also consider an anisotropic variant of the Thomson problem with a mixture of charges. With increasing anisotropy, we first observe the disruption of translational order with an intermediate orientationally ordered hexatic phase as proposed by Nelson, Rubinstein and Spaepen, and then a transition to amorphous state. By analyzing the structure of the disclination motifs induced, we show that the hexaticamorphous transition is caused by the growth and connection of disclination grain boundaries, suggesting this transition lies in the percolation universality class in the scenarios considered.

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“…This can be either topographic, so that curvature is induced by the varying surface normal, or chemical, such that the preferred orientation axis varies across the substrate. In the absence of applied fields, surface coupling and orientational elasticity dominate LC alignment, such that varying a surface pattern can permit full control of both the preferred bulk orientation and its effective anchoring strength 34 . Incompatibility between the surface pattern and the ordering may also promote spontaneous symmetry breaking, in which the LC adopts a surface-region configuration belonging to a subgroup of the pattern’s symmetry group.…”

Section: Introductionmentioning

confidence: 99%

Programming emergent symmetries with saddle-splay elasticity

et al. 2019

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The director field adopted by a confined liquid crystal is controlled by a balance between the externally imposed interactions and the liquid’s internal orientational elasticity. While the latter is usually considered to resist all deformations, liquid crystals actually have an intrinsic propensity to adopt saddle-splay arrangements, characterised by the elastic constant . In most realisations, dominant surface anchoring treatments suppress such deformations, rendering immeasurable. Here we identify regimes where more subtle, patterned surfaces enable saddle-splay effects to be both observed and exploited. Utilising theory and continuum calculations, we determine experimental regimes where generic, achiral liquid crystals exhibit spontaneously broken surface symmetries. These provide a new route to measuring . We further demonstrate a multistable device in which weak, but directional, fields switch between saddle-splay-motivated, spontaneously-polar surface states. Generalising beyond simple confinement, our highly scalable approach offers exciting opportunities for low-field, fast-switching optoelectronic devices which go beyond current technologies.

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Competition of lattice and basis for alignment of nematic liquid crystals

Cited by 6 publications

References 56 publications

Ordering of oblate hard particles between symmetric penetrable walls

Ordering of oblate hard particles between symmetric penetrable walls

Elongation and percolation of defect motifs in anisotropic packing problems

Programming emergent symmetries with saddle-splay elasticity

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