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 twist-bend nematic ($N_{\mathrm{TB}}$) phases, the induced smectic-$A$ ($\mathrm{Sm}-A$) phase for weight fraction of CB7CB between 0.05 and 0.70. In planar nematic layers, the $N_{\mathrm{TB}}$ 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, $\mathrm{Sm}-A$ 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 $\mathrm{Sm}-A$ 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 $\mathrm{Sm}-A$, the low $\mathrm{Sm}-A–N$ 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 $\mathrm{Sm}-A$, is also exhibited by disks nucleating on surfaces treated for homeotropic anchoring.

中文翻译：

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鞍状盘引起的周期性边缘波动在浸入向列介质中的近晶盘状磁盘中

我们报告了关于1“，7”-双（4-氰基联苯-4'-基）庚烷（CB7CB）和4,4-二庚基氧基氮氧基苯的二元混合物的相行为的实验研究，除向列相（$ñ$）和扭曲向列（${ñ}_{\mathrm{结核病}}$）阶段，诱发近晶-$\mathrm{一种}$ （$m-\mathrm{一种}$）相，CB7CB的重量分数在0.05和0.70之间。在平面向列层中，${ñ}_{\mathrm{结核病}}$相分离成类触针状平面状液滴；液滴的手征性表现在其相对角端之间的光学差异。我们的主要结果是，在适当的两相区域，$m-\mathrm{一种}$具有正介电各向异性的原子核转变为浸没在某些电场上方向列相的圆盘，其边缘被周期性的亮点装饰，这一结果早在另一种显示出感应光的二元系统中已有报道。$m-\mathrm{一种}$相[R. Pratibha and NV Madhusudana，Physica A 224，9（1996）]。我们针对这种变形的阈值开发了一种简单的理论，该阈值是圆盘边缘的周期性起伏，表明它是由圆盘的鞍展弹性引起的。$m-\mathrm{一种}$低 $m-\mathrm{一种}–ñ$界面张力无法抑制变形。在两个实验系统中，该模型也说明了所观察到的亮点数量随场的增加以及给定场中磁盘半径的增加。失真导致最直接的可视化鞍形展开$m-\mathrm{一种}$圆盘在经垂直锚固处理的表面上成核，也显示出。