Labyrinthine instability in freely-suspended smectic films

外磁场与流体磁化强度之间的相互作用会引起铁水动力学的不稳定性。这种产生指状和迷宫图案的不稳定性在磁性铁磁流体中非常常见，它不仅表明磁场对流体的直接影响，而且还表明反馈会极大地改变流场。在电极化流体中，特别是在铁电液晶中，也可能出现类似的现象。然而，这种现象以前从未在液晶中观察到过。在我们的研究中，我们发现在自由悬浮的极性密晶薄膜中存在迷宫般的不稳定性。由于薄膜的残余宏观极化，这种不稳定性在没有外加电场的情况下自发发生。本研究的最终目的是研究迷宫式薄膜的生长，并了解其潜在的不稳定性机制。利用显微镜、原子力显微镜、线性电光和SHG等实验技术，对薄膜的结构和在电场中的不稳定行为进行全面的研究。下面的理论分析，基于提出的实验研究，旨在阐明铁电有序和中间相结构在不稳定机制中的潜在作用。本研究的结果不仅对液晶的模式形成有重要的贡献，而且对我们对铁流体动力学不稳定性的一般认识也有重要的贡献。

Interactions between external magnetic field and the magnetization of a fluid can give rise to ferrohydrodynamic instabilities. Such instabilities, yielding fingering and maze patterns, are very common in magnetic ferrofluids and express not only a direct influence of the magnetic field on fluids but also feed back that drastically modifies the flow field. Similar phenomena can also be expected in electrically polarizable fluids or, especially, in ferroelectric liquid crystals. However, such phenomena have never been observed in liquid crystals before. In our studies, we have discovered a labyrinthine instability in freely-suspended polar smectic films. Due to the residual macroscopic polarization of the films this instability occurs spontaneously without externally applied electric field. The ultimate goal of the proposal is to study the labyrinthine growth in the smectic films and to understand the underlying instability mechanisms. A comprehensive study of the film structure an instability behavior in electric fields will be done using various experimental techniques such as microscopy, AFM, linear electro-optics and SHG. A following theoretical analysis, based on the proposed experimental studies, is aimed to elucidate the underlying role of the ferroelectric order and the mesophase structures in the instability mechanism. The outcome of this research project may significantly contribute not only into the pattern formation in liquid crystals but also in our general understanding of ferrohydrodynamic instabilities.