Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, WI 53706, USA.
Proc Natl Acad Sci U S A. 2010 Mar 2;107(9):3998-4003. doi: 10.1073/pnas.0910931107. Epub 2010 Jan 26.
Assemblies formed by solid particles at interfaces have been widely studied because they serve as models of molecular phenomena, including molecular self-assembly. Solid particles adsorbed at interfaces also provide a means of stabilizing liquid-liquid emulsions and synthesizing materials with tunable mechanical, optical, or electronic properties. Whereas many past studies have investigated colloids at interfaces of isotropic liquids, recently, new types of intercolloidal interactions have been unmasked at interfaces of liquid crystals (LCs): The long-range ordering of the LCs, as well as defects within the LCs, mediates intercolloidal interactions with symmetries that differ from those observed with isotropic liquids. Herein, we report the decoration of interfaces formed between aqueous phases and nematic LCs with prescribed densities of solid, micrometer-sized particles. The microparticles assemble into chains with controlled interparticle spacing, consistent with the dipolar symmetry of the defects observed to form about each microparticle. Addition of a molecular surfactant to the aqueous phase results in a continuous ordering transition in the LC, which triggers reorganization of the microparticles, first by increasing the spacing between microparticles within chains and ultimately by forming two-dimensional arrays with local hexagonal symmetry. The ordering transition of the microparticles is reversible and is driven by surfactant-induced changes in the symmetry of the topological defects induced by the microparticles. These results demonstrate that the orderings of solid microparticles and molecular adsorbates are strongly coupled at the interfaces of LCs and that LCs offer the basis of methods for reversible, chemosensitive control of the interfacial organization of solid microparticles.
固-液界面处的固体颗粒组装体已得到广泛研究，因为它们可以作为分子现象的模型，包括分子自组装。固-液界面上吸附的固体颗粒也提供了稳定液-液乳液和合成具有可调机械、光学或电子性能的材料的方法。尽管过去的许多研究都集中在各向同性液体界面处的胶体上，但最近在液晶（LC）界面处揭示了新型胶体间相互作用：LC 的长程有序以及 LC 内的缺陷，介导了具有不同于各向同性液体观察到的对称性的胶体间相互作用。在此，我们报告了在水相和向列 LC 之间形成的界面用预定密度的固体、微米级颗粒进行修饰。这些微颗粒组装成具有受控的颗粒间间隔的链，这与观察到的围绕每个微颗粒形成的缺陷的偶极对称性一致。向水相添加分子表面活性剂会导致 LC 发生连续的有序转变，这会触发微颗粒的重新排列，首先是增加链内微颗粒之间的间隔，最终通过形成具有局部六方对称性的二维阵列。微颗粒的有序转变是可逆的，由微颗粒诱导的拓扑缺陷的对称性因表面活性剂诱导的变化而驱动。这些结果表明，在 LC 的固-液界面处，固体微颗粒和分子吸附剂的有序排列是强烈耦合的，并且 LC 为可逆、化学敏感控制固体微颗粒的界面组织提供了基础。
