PATTERN FORMATION AND SYMMETRY OF FIELDS IN ELECTROHYDRODYNAMICSS IN LIQUID CRYSTALS

液晶电化学场的图案形成和对称性

基本信息

批准号：
08454107
负责人：
KAI Shoichi
金额：
$ 5.06万
依托单位：
KYUHSU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

项目摘要

The electrohydrodynamic instability (EHD) in nematic liquid crystals is investgated using homeotropically aligned systems where the nematic director orients perpendicular to the electrodes. In homeotropically aligned EHD the system has a continuously rotational symmetry as well as a translational one. This symmetry leads to additional new Goldstone modes at onset of convections and dramatically changes the bifurcation properties as well as observed patterns. The obtained results in the present study are as follows.1) In the system with additional Goldstone modes due to continuous rotational symmetry, a direct transition from nonconvective states to spatiotemporal chaos is observed.2) The bifuration at onset occurs supercritically. The correlation time of macroscopic randam motions becomes longer inversely proportional to the deviation from the onset, that is, a critical slowing down phenomenon is observed. From this behavior the spatiotemporal chaos has been named the soft mode turbule … More nce (SMT) .3) The stability of additional Goldstone modes can be controlled by application of magnetic field since magnetic fields induce the prefered axis and suppress the generation of the Goldstone modes. Therefore under superimposing strong magnetic fields periodic patterns are observed.4) New type of zig-zag patterns are found out which are not predicted in currently available thcories.5) It is clarified from these findings that driving forccs which result in SMT are induced by non-parallel orientation between the director and the wavevector of covective rolls.6) Depending on the strength of magnetic fields there are two types of spatiotemporal chaos. The transition between them is clearly defined by looking the spatial power spectra of patterns and distribution functions of roll orientations.7) The rolls exist either in all directions or only in the prefered directions induced by magnetic fields. Then the formet one is called SMT and the latter the defect turbulence.Thus excess of symmetry can result in chaos and the intrinsic mechanism for direct transition to chaos from a spatially uniform state is destabilization of short-wavelength modes due to coupling with Goldstone modes of the spectrum. Based on these results, new theory will be expected in EHD. Less

向列液晶中的电流体动力学不稳定性 (EHD) 使用垂直排列系统进行研究，其中向列指向矢垂直于电极。在垂直排列 EHD 中，系统具有连续旋转对称性以及平移对称性。这种对称性导致了额外的新对称性。对流开始时的戈德斯通模式极大地改变了分叉特性以及观察到的模式，本研究获得的结果如下。1) 在由于连续旋转对称性，系统具有额外的戈德斯通模式，观察到从非对流状态到时空混沌的直接转变。2）开始时的分岔发生超临界，宏观随机运动的相关时间变得更长，与开始的偏差成反比，也就是说，从这种行为中观察到了一种临界减速现象，时空混沌被命名为软模式湍流……更多 nce (SMT) .3) 附加戈德斯通的稳定性。模式可以通过施加磁场来控制，因为磁感应出优选轴并抑制戈德斯通场模式的产生，因此在叠加的强磁场下观察到周期性图案。4）发现了新型锯齿形图案。目前可用的理论中未预测到。5) 从这些发现中可以清楚地看出，导致 SMT 的驱动力是由指向矢和对流滚子的波矢量之间的非平行方向引起的。6) 取决于强度在磁场中，存在两种类型的时空混沌，通过查看图案的空间功率谱和滚动方向的分布函数，可以清楚地定义它们之间的过渡。7）滚动要么存在于所有方向上，要么仅存在于由所引起的首选方向上。前一种称为 SMT，后一种称为缺陷湍流。因此，过度对称会导致混沌，而从空间均匀状态直接转变为混沌的内在机制是由于短波长模式的不稳定。基于这些结果，EHD 中将出现新的理论。