Bechtold I H, Batalioto F, Thieghi L T, Honda B S L, Pojar M, Schoenmaker J, Santos A D, Zucolotto V, Balogh D T, Oliveira O N, Oliveira E A
Departamento de Física, Universidade Federal de Santa Catarina, 88040-900 Florianópolis-SC, Brazil.
Phys Rev E Stat Nonlin Soft Matter Phys. 2006 Aug;74(2 Pt 1):021714. doi: 10.1103/PhysRevE.74.021714. Epub 2006 Aug 31.
The orientational order of liquid crystals (LCs) induced by periodic patterned substrates has been investigated with cells coated by azopolymer films that could be photoaligned in a controlled way. Two regimes were observed depending on the period of the patterns: (i) above 3.0 microm the LC follows the direction imposed by the patterned substrate since the energy stored in the surface potential minimizes the elastic energy of the LC medium. (ii) For periods smaller than 1.0 microm a homogeneous in-plane state was induced and the LC did not follow the orientation imposed by the surface. This in-plane transition could be explained qualitatively by a theoretical model based on the competition between the Frank-Oseen elastic energy and the phenomenological surface potential. The results also suggest an out-of-plane transition for the LC director as the period was reduced. These results agree with data in the literature for patterned substrates with completely distinct architectures. This indicates that for a particular LC sample the overall behavior depends basically on the texture period instead of the texture architecture. The textures were characterized with a scanning near-field optical microscope (SNOM), which allowed simultaneous morphological and optical images in the submicrometer range.
利用可通过光以可控方式取向排列的偶氮聚合物薄膜涂覆的液晶盒，研究了周期性图案化衬底诱导的液晶（LC）的取向有序性。根据图案的周期观察到两种情况：（i）当周期大于3.0微米时，液晶遵循图案化衬底施加的方向，因为存储在表面势中的能量使液晶介质的弹性能最小化。（ii）对于小于1.0微米的周期，会诱导出均匀的面内状态，液晶不遵循表面施加的取向。这种面内转变可以通过基于弗兰克 - 奥森弹性能与唯象表面势之间竞争的理论模型进行定性解释。结果还表明，随着周期减小，液晶指向矢会发生面外转变。这些结果与具有完全不同结构的图案化衬底的文献数据一致。这表明对于特定的液晶样品，整体行为基本上取决于纹理周期而非纹理结构。使用扫描近场光学显微镜（SNOM）对纹理进行了表征，该显微镜能够在亚微米范围内同时获取形态和光学图像。
