Turzi Stefano S
Dipartimento di Matematica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy.
Phys Rev E. 2016 Dec;94(6-1):062705. doi: 10.1103/PhysRevE.94.062705. Epub 2016 Dec 27.
Nematic liquid crystals exhibit both crystallike and fluidlike features. In particular, the propagation of an acoustic wave shows an interesting occurrence of some of the solidlike features at the hydrodynamic level, namely, the frequency-dependent anisotropy of sound velocity and acoustic attenuation. The non-Newtonian behavior of nematics also emerges from the frequency-dependent viscosity coefficients. To account for these phenomena, we put forward a viscoelastic model of nematic liquid crystals, and we extend our previous theory to fully include the combined effects of compressibility, anisotropic elasticity, and dynamic relaxation, at any shear rate. The low-frequency limit agrees with the compressible Ericksen-Leslie theory, while at intermediate frequencies the model correctly captures the relaxation mechanisms underlying finite shear and bulk elastic moduli. We show that there are only four relaxation times allowed by the uniaxial symmetry.
向列型液晶兼具晶体和流体的特性。特别是，声波的传播在流体动力学层面展现出一些类固体特性的有趣现象，即声速和声学衰减的频率依赖性各向异性。向列型液晶的非牛顿行为也源于频率依赖性粘度系数。为了解释这些现象，我们提出了一种向列型液晶的粘弹性模型，并将我们之前的理论进行扩展，以在任何剪切速率下全面纳入可压缩性、各向异性弹性和动态弛豫的综合效应。低频极限与可压缩的埃里克森 - 莱斯利理论一致，而在中频时，该模型正确地捕捉到了有限剪切和体积弹性模量背后的弛豫机制。我们表明，单轴对称仅允许四个弛豫时间。
