Škarabot Miha, Mottram Nigel J, Kaur Supreet, Imrie Corrie T, Forsyth Ewan, Storey John M D, Mazur Rafal, Piecek Wiktor, Komitov Lachezar
Condensed Matter Department, J. Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia.
School of Mathematics and Statistics, University of Glasgow, University Place, Glasgow G12 8QQ, Scotland, U.K.
ACS Omega. 2022 Mar 10;7(11):9785-9795. doi: 10.1021/acsomega.2c00023. eCollection 2022 Mar 22.
Flexoelectricity may have an important impact on the switching properties of nematic and cholesteric liquid crystals due to the linear coupling between the flexoelectric polarization of the liquid crystal and the applied electric field. This coupling is the origin of the extraordinary electro-optic effect in cholesterics aligned in the uniform lying helix texture, resulting in fast switching and field control of both rise and fall times. Therefore, the flexoelectric properties of the liquid crystals have become an important issue when designing and synthesizing liquid crystal materials and/or preparing their mixtures with appropriate flexoelectric compounds (dopants). Here, we report on the flexoelectric polarization of a highly polar nematic liquid crystal host enhanced by doping it with two newly synthesized dopants SK 1-6 and SK 1-8, possessing a hockey stick molecular shape, and comparing their doping effect with the one of the dimeric dopants CB7CB possessing a symmetric bend molecular shape. All dopants were dissolved in small concentration (5 wt %) in the nematic host so that the linear approximation of the dependence of the difference between splay and bend flexoelectric constants, that is, ( - ), on the concentration of the dopant in the host material can be applied. In this way, ( - ) was estimated for the hockey stick dopants SK 1-6 and SK 1-8 to be 0.182 and 0.204 nC/m, respectively. The obtained flexoelectric polarization of these dopants is among the highest reported in the literature so far.
由于液晶的挠曲电极化与外加电场之间的线性耦合，挠曲电效应可能对向列相和胆甾相液晶的开关特性产生重要影响。这种耦合是在均匀平躺螺旋织构中排列的胆甾相液晶中出现非凡电光效应的根源，导致上升和下降时间的快速切换和场控制。因此，在设计和合成液晶材料和/或制备其与合适的挠曲电化合物（掺杂剂）的混合物时，液晶的挠曲电性质已成为一个重要问题。在此，我们报道了一种高极性向列相液晶主体通过掺杂两种新合成的具有曲棍球棒分子形状的掺杂剂SK 1-6和SK 1-8来增强其挠曲电极化，并将它们的掺杂效果与具有对称弯曲分子形状的二聚体掺杂剂CB7CB的掺杂效果进行比较。所有掺杂剂均以低浓度（5 wt%）溶解在向列相主体中，以便可以应用展曲和弯曲挠曲电常数之差（即( - )）对主体材料中掺杂剂浓度的依赖关系的线性近似。通过这种方式，估计曲棍球棒掺杂剂SK 1-6和SK 1-8的( - )分别为0.182和0.204 nC/m。这些掺杂剂获得的挠曲电极化是迄今为止文献报道中最高的之一。
