Small-angle x-ray scattering study of flow alignment of a thermotropic liquid crystal in the nematic and smectic phases
Small-angle x-ray scattering study of flow alignment of a thermotropic liquid crystal in the nematic and smectic phases
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DOI：
10.1103/physreve.74.020701
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发表时间：
2006-08-01
影响因子：
2.4
通讯作者：
Parras, P.
中科院分区：
文献类型：
--
作者：
Hamley, I. W.;Castelletto, V.;Parras, P.
利用时间分辨同步辐射小角X射线散射研究了热致液晶4-正辛基-4（'）-氰基联苯在近晶相和非近晶相的毛细管流动取向。将样品从各向同性相冷却以消除先前的取向。当在圆形毛细管中的Poilluille流动下冷却通过α相时，从介晶沿着流动方向的排列到层沿着流动方向的排列（介晶垂直于流动）的转变似乎在所施加的冷却速率下连续发生。转变集中在Leslie粘度系数α（3）改变符号的温度上。在近晶相中也观察到沿流动方向沿着排列的层的配置。在冷却时的相变在先前已被归因于对准-非对准或翻滚转变。在高流速下，有证据表明，沿流动方向沿着层的平均排列周围有翻滚。在较低的流速下，该取向被更清楚地限定。层对齐归因于表面诱导的有序传播到大部分的毛细管，观察支持的层的平行排列的静态样品中观察到的在低温下在低温下的相变。
The capillary flow alignment of the thermotropic liquid crystal 4-n-octyl-4(')-cyanobiphenyl in the nematic and smectic phases is investigated using time-resolved synchrotron small-angle x-ray scattering. Samples were cooled from the isotropic phase to erase prior orientation. Upon cooling through the nematic phase under Poiseuille flow in a circular capillary, a transition from the alignment of mesogens along the flow direction to the alignment of layers along the flow direction (mesogens perpendicular to flow) appears to occur continuously at the cooling rate applied. The transition is centered on a temperature at which the Leslie viscosity coefficient alpha(3) changes sign. The configuration with layers aligned along the flow direction is also observed in the smectic phase. The transition in the nematic phase on cooling has previously been ascribed to an aligning-nonaligning or tumbling transition. At high flow rates there is evidence for tumbling around an average alignment of layers along the flow direction. At lower flow rates this orientation is more clearly defined. The layer alignment is ascribed to surface-induced ordering propagating into the bulk of the capillary, an observation supported by the parallel alignment of layers observed for a static sample at low temperatures in the nematic phase.