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Elastic constants of splay K_11, twist K_22, and bend K_33 of nematic liquid crystals are often assumed to be equal to each other in order to simplify the theoretical description of complex director fields. Here we present examples of how the disparity of K_11 and K_33 produces effects that cannot be described in a one-constant approximation. In a lyotropic chromonic liquid crystal, nematic droplets coexisting with the isotropic phase change their shape from a simply-connected tactoid to a topologically distinct toroid as a result of temperature or concentration variation. The transformation is caused by the increase of the splay-to-bend ratio K_11/K_33. A phase transition from a conventional nematic to a twist-bend nematic implies that the ratio K_11/K_33 changes from very large to very small. As a result, the defects caused by an externally applied electric field change the deformation mode of optic axis from bend to splay. In the paraelectric-ferroelectric nematic transition, one finds an inverse situation: K_11/K_33 changes from small to large, which shapes the domain walls in the spontaneous electric polarization field as conic sections. The polarization field tends to be solenoidal, or divergence-free, a behavior complementary to irrotational curl-free director textures of a smectic A.
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Soliton walls paired by polar surface interactions in a ferroelectric nematic liquid crystal
Abstract Surface interactions are responsible for many properties of condensed matter, ranging from crystal faceting to the kinetics of phase transitions. Usually, these interactions are polar along the normal to the interface and apolar within the interface. Here we demonstrate that polar in-plane surface interactions of a ferroelectric nematic N F produce polar monodomains in micron-thin planar cells and stripes of an alternating electric polarization, separated by $${180}^{{{{{{\rm{o}}}}}}}$$ 180 o domain walls, in thicker slabs. The surface polarity binds together pairs of these walls, yielding a total polarization rotation by $${360}^{{{{{{\rm{o}}}}}}}$$ 360 o . The polar contribution to the total surface anchoring strength is on the order of 10%. The domain walls involve splay, bend, and twist of the polarization. The structure suggests that the splay elastic constant is larger than the bend modulus. The $${360}^{{{{{{\rm{o}}}}}}}$$ 360 o pairs resemble domain walls in cosmology models with biased vacuums and ferromagnets in an external magnetic field.
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- Award ID(s):
- 2122399
- PAR ID:
- 10428948
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 13
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1038/s41467-022-31593-w
