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arXiv 2602.23150cond-mat.softphysics.flu-dyn
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铁电向列液态晶体的流变性质和剪切诱导结构

Rheological properties and shear-induced structures of ferroelectric nematic liquid crystals

Kent State University(肯特州立大学)

Ashish Chandra Das, Sathyanarayana Paladugu, Oleg D. Lavrentovich

AI总结:

研究铁电向列液态晶体在剪切流下的流变性质和结构行为,揭示其粘度与剪切速率的关系及对齐机制。

摘要:

最近发现的铁电向列(NF)液态晶体是一种具有极性定向序的流体。电极化矢量可通过电场和表面锚定进行对齐。本文探讨了剪切流如何影响NF材料的极化场和有效粘度。我们研究了三种NF材料,分别简称为RM734、DIO和室温FNLC919,它们都表现出顺电向列(N)和NF相。所有材料在冷却时粘度增加,表现出阿伦尼乌斯行为。在DIO和FNLC919中,反铁电SmZA相的粘度对剪切速率有强依赖性:在高剪切速率下,该粘度低于N和NF相的粘度,但在低剪切速率下则高得多。这种行为与SmZA相的层状结构有关。所有各向同性相在低剪切速率下表现出剪切稀释行为,在高剪切速率下表现出近牛顿行为。在对齐方面,我们观察到N和NF相的三个阶段:低剪切速率下的流动对齐、高剪切速率下的涡旋轴对齐阶段以及中间速率下的多域结构。在流动对齐阶段,NF的极化方向不远离剪切方向,这与N相的流动诱导倾斜方向形成鲜明对比。这种效应归因于避免了张开变形和相关的空间电荷在流动NF中的产生。粘度的温度和剪切速率依赖性以及揭示的剪切诱导结构效应使我们对这些材料的理解更深入,并可能促进其应用。

英文摘要:

Recently discovered ferroelectric nematic (NF) liquid crystals are fluids with a polar orientational order. The electric polarization vector can be aligned by an electric field and by surface anchoring. Here, we explore how the polarization field and effective viscosity of the NF materials are affected by shear flows. We explore three NF materials, abbreviated RM734, DIO, and a room-temperature FNLC919, all of which exhibit a paraelectric nematic (N) and the NF phase. All materials show an increase of the viscosity upon cooling, with an Arrhenius behavior. In DIO and FNLC919, the antiferroelectric SmZA phase shows a strong dependence of the effective viscosity on the shear rate: this viscosity is lower than the viscosity of the N and NF phases at high shear rates but is much higher when the shear rate is low. The behavior is associated with the layered structure of the SmZA phase. All mesophases exhibit shear-thinning behavior at low shear rates and a nearly Newtonian behavior at higher shear rates. In terms of alignment, we observe three regimes in the N and NF phases: flow-alignment at low shear rates, log-rolling regime with the director and polarization along the vorticity axis at high shear rates, and polydomain structures at intermediate rates. In the flow-aligning regime, the NF polarization does not tilt away from the shear direction, which is in sharp contrast to the flow-induced tilt of the N director. The effect is attributed to the avoidance of splay deformations and associated space charge in the flowing NF. The temperature and shear rate dependencies of the viscosity and the uncovered shear-induced structural effects of NF advance our understanding of these materials and potentially facilitate their applications.

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