Observation and simulation of toron polymorphism: Effects of surface anchoring, elasticity and electric field in cholesterics with smectic-A phase beneath
Observation and simulation of toron polymorphism: Effects of surface anchoring, elasticity and electric field in cholesterics with smectic-A phase beneath
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Toron 多晶型的观察与模拟：表面锚定、弹性和电场对下方近晶 A 相的胆甾醇的影响
DOI：
10.1016/j.molliq.2021.118454
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发表时间：
2022
影响因子：
6
通讯作者：
T. Sasaki
中科院分区：
文献类型：
--
作者：
K. V. Le;S. Aya;J. Kougo;S. Takahashi;T. Takezoe;Y. Naka;T. Sasaki
Toron是许多自旋电子学和软物质系统中出现的基本手征拓扑织构之一。本文报道了在具有正介电各向异性（Δε> 0）的双折射液晶中观察到的Torons。此外，材料显示出近晶相下的近晶-A相，使我们能够看到预转变的影响，形成的torons。详细研究了温度、电场等外界刺激与托龙成形性的关系。重要的是，在向列-近晶-A相变附近的弹性常数（K22和K33）的发散导致从toron到垂面排列的转变。结果表明，无论是垂面锚定强度和沮丧的限制的螺旋是重要的，以确定是否选择托龙纹理之间的其他纹理，如手指。约束比，即细胞厚度的比例，以螺旋桨间距，为入射的torons被发现是在一个很宽的范围内约0.82 × 1.5。我们还表明，torons可以聚合物稳定，使他们保留在一个很宽的温度窗口。更重要的是，聚合物稳定的托伦的取向状态可以通过电场改变，实现暗态和亮态之间的快速切换。该系统可以在电驱动衍射光栅或具有亚毫秒响应时间的隐私保护膜中找到应用。
Toron is one of the fundamental chiral topological textures appearing in many spintronic and soft matter systems. Here we report on the observation of torons in cholesteric liquid crystals with positive dielectric anisotropy (Δε> 0). In addition, the materials show smectic-A phase beneath the cholesteric phase, enabling us to see the pretransitional effect on the formation of the torons. In detail, we investigated the relation of toron formability and the external stimuli in terms of temperature and electric field. Importantly, the divergence of the elastic constants (K 22 and K 33) in the vicinity of the nematic-smectic-A phase transition causes the transition from the toron to the homeotropic alignment. The results reveal that both the homeotropic anchoring strength and the frustrated confinement of the cholesteric helix are important to determine whether the toron texture is selected among other textures like fingers. The confinement ratio, ie the ratio of cell thickness to cholesteric pitch, for the incidence of torons was found to be in a wide range of about 0.82∼ 1.5. We also show that the torons can be polymer-stabilized so that they retain over a wide temperature window. Even more importantly, the orientational state of the polymer-stabilized toron can be changed by an electric field, realizing fast switching between the dark and bright states. The system may find applications in electric-driven diffraction gratings or privacy protection films with a sub-millisecond response time.