RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Soft Matter. 2019 Jan 30;15(5):989-998. doi: 10.1039/c8sm01751d.
Using a photo-responsive dimer exhibiting the transition between nematic (N) and twist-bend nematic (NTB) phases, we prepared spherical cap-shaped droplets on solid substrates exposed to air. The internal director structures of these droplets vary depending on the phase and on the imposed boundary conditions. The structural switching between the N and NTB phases was successfully performed either by temperature control or by UV light-irradiation. The N phase is characterized by an extremely small bend elastic constant K3, and surprisingly, we found that the droplet-air interface induces a planar alignment, in contrast to that seen for typical calamitic liquid crystals. As a consequence, the director configuration was stabilized in a structure substantially different from that normally found in conventional nematic liquid crystalline droplets. In the twist-bend nematic droplets characteristic structures with macroscopic length scales were formed, and they were well controlled by the droplet size. These results indicated that a continuum theory is effective in describing the stabilization mechanism of the macroscopic structure even in the twist-bend nematic liquid crystal droplets exhibiting director modulations on a scale of several molecular lengths.
利用一种光响应二聚体，展示了向列（N）相和扭曲向列（NTB）相之间的转变，我们在暴露于空气的固体基底上制备了球形帽状液滴。这些液滴的内部指向矢结构取决于相和所施加的边界条件。通过温度控制或紫外光照射成功地实现了 N 相和 NTB 相之间的结构转换。N 相的特点是极其小的弯曲弹性常数 K3，令人惊讶的是，我们发现液滴-空气界面诱导出平面排列，与典型的棒状液晶不同。因此，指向矢配置在与通常在常规向列液晶液滴中发现的结构显著不同的结构中稳定下来。在扭曲向列向列液滴中形成了具有宏观长度尺度的特征结构，并且它们可以通过液滴尺寸很好地控制。这些结果表明，即使在扭曲向列向列液晶液滴中，在几个分子长度的尺度上表现出指向矢调制，连续体理论也可以有效地描述宏观结构的稳定机制。
