Q-tensor model for electrokinetics in nematic liquid crystals
Q-tensor model for electrokinetics in nematic liquid crystals
复制标题
DOI：
10.1103/physrevfluids.2.053302
复制
发表时间：
2017-05-05
影响因子：
2.7
通讯作者：
Walkington, Noel J.
中科院分区：
文献类型：
--
作者：
Tovkach, O. M.;Conklin, Christopher;Walkington, Noel J.
我们利用变分原理推导出向列相电解液的数学模型，其中液晶组分用二阶参数张量来描述。该模型扩展了先前发展的基于董事的理论，并解释了倾向性和可能的双轴性的存在。我们通过考虑一个简单但说明性的例子来验证这个模型，这个例子是液晶使能的电渗流绕着放置在一个装满向列相电解液的大圆柱形容器的中心的静止的电介质球粒子。假设向列相在粒子表面锚定，指向矢在容器表面均匀分布，我们分别考虑了两种构型，一种是倾斜赤道环，另一种是双曲刺猬。计算的电渗流显示出强烈的依赖于指向矢组态和向列相的介电常数和电导率的各向异性，这是液晶使能电动力学的特征。此外，模拟表明，即使在各向同性介电常数和电导率的情况下，介电球体周围的空间电荷也是分离的。这与各向同性电解液中发生的感应电荷电渗透效应是一致的，当外加电场作用于它在可极化表面附近诱导的离子电荷时。
We use a variational principle to derive a mathematical model for a nematic electrolyte in which the liquid crystalline component is described in terms of a second-rank order parameter tensor. The model extends the previously developed director-based theory and accounts for the presence of disclinations and possible biaxiality. We verify the model by considering a simple but illustrative example of liquid crystal-enabled electro-osmotic flow around a stationary dielectric spherical particle placed at the center of a large cylindrical container filled with a nematic electrolyte. Assuming homeotropic anchoring of the nematic on the surface of the particle and uniform distribution of the director on the surface of the container, we consider two configurations with a disclination equatorial ring and with a hyperbolic hedgehog, respectively. The computed electro-osmotic flows show a strong dependence on the director configurations and on the anisotropies of dielectric permittivity and electric conductivity of the nematic, characteristic of liquid crystal-enabled electrokinetics. Further, the simulations demonstrate space charge separation around the dielectric sphere, even in the case of isotropic permittivity and conductivity. This is in agreement with the induced-charge electroosmotic effect that occurs in an isotropic electrolyte when an applied field acts on the ionic charge it induces near a polarizable surface.