Abstract
We report experimental studies on the phase behavior of binary mixtures of 1″,7″-bis(4-cyanobiphenyl-4′-yl)heptane (CB7CB) and 4,4-diheptyloxyazoxybenzene, which exhibit, apart from the nematic () and twist-bend nematic () phases, the induced smectic- () phase for weight fraction of CB7CB between 0.05 and 0.70. In planar nematic layers, the phase separates as droplets of tactoidlike planform; the chirality of droplets manifests in the optical dissimilarity between their opposite angular ends. Our main result is that, in the appropriate two phase region, nuclei with positive dielectric anisotropy change over to disks immersed in the nematic above some electric field, their edges decorated by periodic bright spots, a result which was earlier reported in another binary system exhibiting the induced phase [R. Pratibha and N. V. Madhusudana, Physica A 224, 9 (1996)]. We develop a simple theory for the threshold of this distortion, which is a periodic undulation of the edge of the disk, demonstrating that it arises from saddle-splay elasticity of , the low interfacial tension unable to suppress the distortion. The observed increases in the number of bright spots with field, and with the radius of the disk at a given field, in both the experimental systems are also accounted for by the model. The distortion, which results in the most direct visualization of saddle splay in , is also exhibited by disks nucleating on surfaces treated for homeotropic anchoring.
10 More- Received 19 December 2019
- Accepted 26 February 2020
DOI:https://doi.org/10.1103/PhysRevE.101.032704
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