School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK.
Soft Matter. 2018 Dec 12;14(48):9819-9829. doi: 10.1039/c8sm01583j.
We demonstrate how the geometric shape of a rod in a nematic liquid crystal can stabilise a large number of oppositely charged topological defects. A rod is of the same shape as a sphere, both having genus g = 0, which means that the sum of all topological charges of defects on a rod has to be -1 according to the Gauss-Bonnet theorem. If the rod is straight, it usually shows only one hyperbolic hedgehog or a Saturn ring defect with negative unit charge. Multiple unit charges can be stabilised either by friction or large length, which screens the pair-interaction of unit charges. Here we show that the curved shape of helical colloids or the grooved surface of a straight rod create energy barriers between neighbouring defects and prevent their annihilation. The experiments also clearly support the Gauss-Bonnet theorem and show that topological defects on helices or grooved rods always appear in an odd number of unit topological charges with a total topological charge of -1.
我们展示了棒状分子在向列相液晶中如何稳定大量的相反电荷的拓扑缺陷。棒状分子的形状与球状分子相同，两者的亏格 g = 0，这意味着根据高斯-博内定理，棒状分子上所有拓扑缺陷的总拓扑电荷必须为-1。如果棒是直的，它通常只显示一个双曲 hedgehog 或带有负单位电荷的 Saturn 环缺陷。多个单位电荷可以通过摩擦或较大的长度来稳定，这可以屏蔽单位电荷的相互作用。在这里，我们表明螺旋胶体的弯曲形状或直棒的凹槽表面在相邻缺陷之间产生了能量障碍，从而阻止了它们的湮灭。实验也清楚地支持了高斯-博内定理，并表明螺旋或有槽棒上的拓扑缺陷总是以奇数个单位拓扑电荷出现，总拓扑电荷为-1。
