Permeative flows in cholesterics: shear and Poiseuille flows.
Permeative flows in cholesterics: shear and Poiseuille flows.
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胆甾醇中的渗透流：剪切流和泊肃叶流。
DOI：
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发表时间：
2006
影响因子：
4.4
通讯作者：
J. Yeomans
中科院分区：
文献类型：
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作者：
D. Marenduzzo;E. Orlandini;J. Yeomans
通过求解描述液晶流体动力学的Beris-Edwards运动方程的格子Boltzmann格式，我们研究了胆甾体对剪切和泊松流动的响应。我们关注的几何是沿螺旋轴方向的流动，这是已知的引起渗透的流动。对于剪切流和泊松叶流，我们发现指向矢场上的边界条件对决定液晶的流变性是至关重要的。对于钉扎在边界上的螺旋，较小的强迫导致较大的粘度增加，而较强的强迫导致向牛顿值急剧下降。这种剪切变薄行为与实验和前人的分析结果是一致的。另一方面，如果导向器可以在壁上自由旋转，则根据稳态主流的对称性，会发现不同的行为。将所考虑的一些情况与类似的外加流动进行了比较，但螺旋线垂直于平板，因此没有观察到粘度增加。
By using a lattice Boltzmann scheme that solves the Beris-Edwards equations of motion describing liquid-crystal hydrodynamics, we study the response of cholesterics to shear and Poiseuille flows. The geometry we focus on is a flow along the direction of the helical axis, which is known to give rise to permeation. For both shear and Poiseuille flow we find that the boundary conditions on the director field are crucial in determining the rheological properties of the liquid crystal. For helices pinned at the boundaries, a small forcing leads to a large viscosity increase whereas a stronger forcing induces a sharp decrease towards the Newtonian value. This shear thinning behavior is in agreement with experiments and previous analytic results. If, on the other hand, the director is free to rotate at the walls, different behaviors are found depending on the symmetry of the steady-state primary flow. Some of the cases considered are compared to a similar imposed flow but with the helix lying perpendicular to the plates, for which no viscosity increase is observed.