Rupture Dynamics and Buckling Instabilities of Free-Standing Liquid Crystal Bridges and Filaments

一维的、独立的流体结构在自然界中并不常见，但可以由任何能够克服毛细(瑞利-高原)不稳定性的材料形成。一旦这种不稳定性被抑制，就可能形成长径比超过1000的长丝。早期关于独立的液晶细丝和电桥的报告测量了它们的机械、声学和电学稳定性。另一个重要的方面，几乎没有报道，是导致断裂或导致纤维在压缩应力下屈曲的不稳定性的影响。对这类过程的定量知识在食品工业中发现了控制大液体薄片或绳索以进行大规模生产的必要性。能够形成稳定细丝的物质具有某种内部结构。由此产生的断裂和屈曲动力学比粘性牛顿流体的断裂和屈曲动力学要复杂得多。在这个研究计划中，我们计划系统地研究盘状和弯曲芯液晶形成的细丝的夹断、断裂动力学、屈曲不稳定性和流动特性。液晶是独一无二的，因为它们的性质在很大程度上取决于存在的取向和位置有序度。这一性质使液晶有别于其他粘性的非牛顿流体。我们试图回答的一些问题如下：变薄、夹断和断裂过程的动力学是什么？桥或细丝上和内部的拓扑缺陷在断裂过程中是如何演变的？它们对破裂过程有什么影响？这样的构造过程与弹性力(方向和位置)有什么关系？

One-dimensional, free-standing fluid structures are not often found in nature, but may be formed by any material that can overcome capillary (Rayleigh-Plateau) instability. Once this instability is suppressed, long filaments, with length-to-diameter ratios exceeding 1000, may be formed.Earlier reports on free-standing liquid crystal filaments and bridges measured their mechanical, acoustical, and electrical stability. Another important aspect, on which there are few reports, is the effect of instabilities that lead to rupture or cause the filament to buckle under compression stress. Quantitative knowledge of such processes has found necessity in the food industry for controlling large liquid sheets or ropes for mass production.Substances capable of forming stable filaments have some sort of internal structure. The resulting rupture and buckling dynamics are substantially more complicated than those for viscous Newtonian fluids.In this research program, we plan to systematically study the pinch-off, rupture dynamics, buckling instabilities, and flow characteristics of filaments formed from discotic and bent-core liquid crystals. Liquid crystals are unique because their properties depend greatly on the amount of orientational and positional ordering present. This property distinguishes liquid crystals from other viscous non-Newtonian fluids.Some of the questions we seek to answer are as follows:What are the dynamics of the thinning, pinch-off, and rupture process?How do topological defects on and within the bridge or filament evolve during the rupture process? What effect do they have on the rupture process?How do such structuring processes relate to the elastic forces (orientational and positional)?