Topological colloids
Topological colloids
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DOI：
10.1038/nature11710
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发表时间：
2013-01-10
期刊：
影响因子：
64.8
通讯作者：
Smalyukh, Ivan I.
中科院分区：
文献类型：
--
作者：
Senyuk, Bohdan;Liu, Qingkun;Smalyukh, Ivan I.
烟、雾、果冻、油漆、牛奶和剃须膏是胶体的常见日常例子，胶体是一种由分散在化学性质不同的基质中的微小颗粒组成的软物质。胶体在自然界中含量丰富，在科学和技术中的应用也越来越重要，从直接探测晶体和玻璃中的动力学（2）到制造第三代量子点太阳能电池（3）。由于天然存在的胶体具有通常由界面张力最小化（例如，在相分离期间）或多面晶体生长（1）确定的形状，因此它们的表面倾向于具有最小面积的球形或拓扑等效形状，例如棱柱和不规则颗粒（所有连续可变形-同胚-为球形）。虽然可以存在具有不同数量手柄的环形DNA凝聚物和囊泡（4-7），并且软物质缺陷可以形成为环（8）和结（9），但胶体系统中颗粒拓扑结构的作用仍然未被探索。在这里，我们制造和研究不同数量的手柄和属g范围从1到5的胶体颗粒。当被引入到一种由杆状分子组成的液体中时，这些粒子自发地沿着所谓的“导向器”（10）沿着，诱导出三维导向场和由胶体拓扑结构决定的拓扑缺陷。尽管电场、光热熔化和激光镊子导致粒子诱导结构的构型之间的转换，三维非线性光学成像揭示了拓扑电荷是守恒的，并且粒子诱导缺陷的总电荷总是服从高斯-邦尼和庞加莱-霍普夫指数定理的预测（11-13）。这使我们能够建立和实验测试的程序分配和求和的拓扑电荷在三维导演领域。我们的发现为胶体和液晶的新应用奠定了基础，这些应用从拓扑存储器件（14），通过新型自组装（15-23），到低维拓扑的实验研究（6，7，11 -13）。
Smoke, fog, jelly, paints, milk and shaving cream are common everyday examples of colloids(1), a type of soft matter consisting of tiny particles dispersed in chemically distinct host media. Being abundant in nature, colloids also find increasingly important applications in science and technology, ranging from direct probing of kinetics in crystals and glasses(2) to fabrication of third-generation quantum-dot solar cells(3). Because naturally occurring colloids have a shape that is typically determined by minimization of interfacial tension (for example, during phase separation) or faceted crystal growth(1), their surfaces tend to have minimum-area spherical or topologically equivalent shapes such as prisms and irregular grains (all continuously deformable-homeomorphic-to spheres). Although toroidal DNA condensates and vesicles with different numbers of handles can exist(4-7) and soft matter defects can be shaped as rings(8) and knots(9), the role of particle topology in colloidal systems remains unexplored. Here we fabricate and study colloidal particles with different numbers of handles and genus g ranging from 1 to 5. When introduced into a nematic liquid crystal-a fluid made of rod-like molecules that spontaneously align along the so-called 'director'(10)-these particles induce three-dimensional director fields and topological defects dictated by colloidal topology. Whereas electric fields, photothermal melting and laser tweezing cause transformations between configurations of particle-induced structures, three-dimensional nonlinear optical imaging reveals that topological charge is conserved and that the total charge of particle-induced defects always obeys predictions of the Gauss-Bonnet and Poincare-Hopf index theorems(11-13). This allows us to establish and experimentally test the procedure for assignment and summation of topological charges in three-dimensional director fields. Our findings lay the groundwork for new applications of colloids and liquid crystals that range from topological memory devices(14), through new types of self-assembly(15-23), to the experimental study of low-dimensional topology(6,7,11-13).