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Title: Saddle-splay-induced periodic edge undulations in smectic-A disks immersed in a nematic medium
Authors: Krishnamurthy, Kanakapura S
Rao, Shankar D.S.
Kanakala, Madhu B
Yelamaggad, C.V.
Madhusudana, N.V.
Issue Date: Mar-2020
Publisher: American Physical Society
Citation: Physical Review E, 2020, Vol.101, Article No.032704
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 (N) and twistbend nematic (NTB) phases, the induced smectic-A (Sm-A) phase for weight fraction of CB7CB between 0.05 and 0.70. In planar nematic layers, the NTB 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, Sm-A 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 Sm-A 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 Sm-A, the low Sm-A–N interfacial tension unable to suppress the distortion. The observed increases in the number of brightspots 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 Sm-A, is also exhibited by disks nucleating on surfaces treated for homeotropic anchoring.
Description: Open Access
ISSN: 2470-0045
2470-0053 (Online)
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Copyright: 2020 American Physical Society
Appears in Collections:Research Papers (SCM)

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