AN EXPERIMENTAL INVESTIGATION OF ELECTROMECHANICAL COUPLING IN CHOLESTERIC LIQUID-CRYSTALS
AN EXPERIMENTAL INVESTIGATION OF ELECTROMECHANICAL COUPLING IN CHOLESTERIC LIQUID-CRYSTALS
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DOI：
10.1080/02678298908045691
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发表时间：
1989-01-01
期刊：
影响因子：
2.2
通讯作者：
PRATIBHA, R
中科院分区：
文献类型：
--
作者：
MADHUSUDANA, NV;PRATIBHA, R
具有定向手性分子螺旋排列的胆甾液晶有望在通量和力之间表现出新的交叉耦合。这些耦合最令人信服的证明是通过对结构的动态影响。虽然莱曼在1900年发现了温度梯度下结构的旋转，但后来没有实验证实这一点。我们认为，在固体胆甾界面上获得一个足够弱的定向物锚定是非常困难的，而这是莱曼旋转发生的必要条件。为了在表面实现几乎为零的锚定能量，我们设计了一种简单的技术，即在各向同性阶段漂浮基本平坦的胆甾滴。利用这种结构，我们研究了在直流电场作用下产生结构旋转的机电耦合。通过对不同螺距值的样品进行测量，发现所研究材料的相关机电系数满足关系= - 0·6 × 10−12(q/m−1)J m−2，其中螺旋的波向量，其符号为正（负），对于右（左）手结构，证实了它的起源是水动力的。
Cholesteric liquid crystals which have a helical arrangement of oriented chiral molecules are expected to show novel cross couplings between fluxes and forces. The most convincing demonstration of these couplings is through a dynamical effect on the structure. Though Lehmann found a rotation of the structure under a temperature gradient in 1900, there has been no subsequent experiment confirming the same. We argue that it is very difficult to obtain a sufficiently weak anchoring of the director at the solid-cholesteric interface which is a necessary condition for the occurrence of Lehmann rotation. In order to achieve a practically zero anchoring energy at the surface, we have devised a simple technique of floating essentially flat cholesteric drops in the isotropic phase. Using this configuration we study the electromechanical coupling which produces a rotation of the structure under the action of a DC electric field. Using measurements on samples with different values of the pitch the relevant electromechanical coefficient of the materials investigated is found to satisfy the relationvE= −0·6 × 10−12(q/m−1)J m−2, whereqis the wavevector of the helix, whose sign is positive (negative) for a right (left) handed structure, confirming thatvEis hydrodynamic in origin.