Buscaglia M, Bellini T, Chiccoli C, Mantegazza F, Pasini P, Rotunno M, Zannoni C
Dipartimento di Chimica, Biochimica e Biotecnologie per la Medicina, Università di Milano, Via F.lli Cervi 93, 20090 Segrate (MI), Italy.
Phys Rev E Stat Nonlin Soft Matter Phys. 2006 Jul;74(1 Pt 1):011706. doi: 10.1103/PhysRevE.74.011706. Epub 2006 Jul 17.
We present a combined experimental and Monte Carlo study of a nematic phase in the presence of quenched disorder. The turbidity of a nematic liquid crystal embedded in a porous polymer membrane is measured under different applied field conditions for field-cooled and zero-field-cooled samples. We find that a significant permanent alignment of the nematic can be induced by fields as low as 0.1 V/microm applied during the isotropic to nematic transition. An analogous effect and dependence on sample history is found by studying the order parameter of a sprinkled disorder Lebwohl-Lasher spin model, indicating that dilute quenched randomness is sufficient to produce memory effects in nematics. The large memory induced by field cooling appears to be written in the system during the transition as a result of the field action on freely oriented nematic nuclei. At lower temperature the nuclei consolidate into permanent nematic textures developed from the interaction with quenched disorder.
我们展示了一项关于存在猝灭无序时向列相的实验与蒙特卡罗相结合的研究。在不同的外加场条件下，对场冷和零场冷样品测量了嵌入多孔聚合物膜中的向列型液晶的浊度。我们发现，在从各向同性到向列相转变期间施加低至0.1 V/微米的场就能诱导向列相产生显著的永久取向。通过研究散布无序的勒布霍尔-拉舍自旋模型的序参量，发现了类似的效应以及对样品历史的依赖性，这表明稀有的猝灭随机性足以在向列相中产生记忆效应。场冷所诱导的大记忆似乎是在转变过程中由于场对自由取向的向列核的作用而写入系统的。在较低温度下，这些核通过与猝灭无序的相互作用巩固为形成的永久向列织构。
