Coursault Delphine, Zappone Bruno, Coati Alessandro, Boulaoued Athmane, Pelliser Laurent, Limagne Denis, Boudet Nathalie, Ibrahim Bicher Haj, de Martino Antonello, Alba Michel, Goldmann Michel, Garreau Yves, Gallas Bruno, Lacaze Emmanuelle
CNRS UMR 7588, Sorbonne Universités, UPMC Univ Paris 06, Institut des NanoSciences de Paris (INSP), 4 place Jussieu, 75005 Paris, France.
Soft Matter. 2016 Jan 21;12(3):678-88. doi: 10.1039/c5sm02241j. Epub 2015 Nov 13.
Combining optical microscopy, synchrotron X-ray diffraction and ellipsometry, we studied the internal structure of linear defect domains (oily streaks) in films of a smectic liquid crystal 8CB with thicknesses in the range of 100-300 nm. These films are confined between air and a rubbed PVA polymer substrate which imposes hybrid anchoring conditions (normal and unidirectional planar, respectively). We show how the presence or absence of dislocations controls the structure of highly deformed thin smectic films. Each domain contains smectic layers curved in the shape of flattened hemicylinders to satisfy both anchoring conditions, together with grain boundaries whose size and shape are controlled by the presence of dislocation lines. A flat grain boundary normal to the interface connects neighboring hemicylinders, while a rotating grain boundary (RGB) is located near the axis of curvature of the cylinders. The RGB shape appears such that dislocation lines are concentrated at its summit close to the air interface. The smectic layers reach the polymer substrate via a transition region where the smectic layer orientation satisfies the planar anchoring conditions over the entire polymer substrate and whose thickness does not depend on that of the film. The strength of planar anchoring appears to be high, larger than 10(-2) mJ m(-2), compensating for the high energy cost of creating an additional 2D defect between a horizontal smectic layer and perpendicular ones of the transition region. This 2D defect may be melted, in order to avoid the creation of a transition region structure composed of a large number of dislocations. As a result, linear defect domains can be considered as arrays of oriented defects, straight dislocations of various Burger vectors, whose location is now known, and 2D nematic defects. The possibility of easy variation between the present structure with a moderate amount of dislocations and a structure with a large number of dislocations is also demonstrated.
结合光学显微镜、同步辐射X射线衍射和椭偏仪，我们研究了厚度在100 - 300纳米范围内的近晶型液晶8CB薄膜中线性缺陷畴（油纹）的内部结构。这些薄膜被限制在空气和经过摩擦的PVA聚合物基板之间，该基板施加了混合锚定条件（分别为法向和单向平面锚定）。我们展示了位错的存在与否如何控制高度变形的近晶型薄膜的结构。每个畴包含呈扁平半圆柱形状弯曲的近晶层，以满足两种锚定条件，同时还包含晶界，其尺寸和形状由位错线的存在控制。垂直于界面的平坦晶界连接相邻的半圆柱，而旋转晶界（RGB）位于圆柱曲率轴附近。RGB的形状使得位错线集中在其靠近空气界面的顶部。近晶层通过一个过渡区域到达聚合物基板，在该过渡区域中，近晶层的取向在整个聚合物基板上满足平面锚定条件，并且其厚度不依赖于薄膜的厚度。平面锚定的强度似乎很高，大于10^(-2) mJ m^(-2)，补偿了在水平近晶层和过渡区域的垂直近晶层之间创建额外二维缺陷的高能量成本。为了避免形成由大量位错组成的过渡区域结构，这种二维缺陷可能会被熔化。结果，线性缺陷畴可以被视为定向缺陷、具有各种伯格斯矢量的直位错（其位置现在已知）以及二维向列型缺陷的阵列。还展示了在具有适量位错的当前结构和具有大量位错的结构之间容易变化的可能性。
