# Perspectives in Liquid-Crystal-Aided Nanotechnology and Nanoscience
## 4 LC-Aided-Assembly and Self-Assembly of Nanomaterials  
As we have seen, nanomaterials show unique physical and chemical properties that are significantly different from bulk materials as well as from individual atoms and molecules. However, single nanomaterial entities cannot be directly applied in functional devices. The generation of macroscopic assemblies of nanomaterials with controlled localization and orientation is necessary for their practical application. A common method is to use a \"bottom-up\" approach whereby functional nanomaterials are designed and directed through self-organization into a particular structure, which requires the targeted ability to manipulate interactions between nanomaterials. To this end, the properties of self-organization of LCs may be exploited. The unique ability of LC materials to self-assemble into long-range ordered superstructures has been widely used as a potential method for synthesizing various functional materials with complicated spatial structures. By virtue of the chemical reactions performed in aqueous lyotropic LCs, different mesoporous materials have been successfully obtained [304]. In addition, thermotropic LCs can also act as an appropriate medium to design \"top-down\" approaches. LCs composed of anisotropic molecules possess a long-range orientational or even positional order and a high susceptibility to various external stimuli. Thanks to these properties, anisotropic torques and forces will be imposed on the micro-additives when they are dispersed in a LC matrix, which will also direct them on a macroscopic scale or even arrange their position on specific micro-scale locations. In the past several decades, a large number of studies have demonstrated the interactions between microparticles in LCs [145; 147; 148; 305; 306] as well as between microparticles and LC defects [137; 307; 308]. Some of them even reported the successful fabrication of complex periodic superstructures consisting of microparticles [146; 149; 150; 154; 308; 309]. However, when it comes to the nanoscale, the problem becomes much more complicated because of the uncontrolled aggregation as well as the limited number of effective characterization methods. Nanoparticles localized in distorted LC regions can effectively decrease the free energy of the system due to the release of the elastic energy generated by the volume occupied by the nanoparticles. In the presence of a distortion gradient, the nanoparticles tend to be automatically dragged into the centre of the distortion [310; 311; 312; 313]. As a result, topological defects, which are the cores surrounded by strongly elastically distorted regions, are usually used as templates for the bottom-up assembly of nanoparticles [314]. Moreover, in the case of anisotropic nanoparticles, the surface anchoring energy plays a vital role in the orientation of nanoparticles. With tangential anchoring, the particles tend to align along the nematic director, while, with radial anchoring, the alignment of the particles tends to be perpendicular to the director. Furthermore, nanoparticles suspended in LCs with a given anchoring energy at the surface will induce a local deformation of LC director field. According to the studies of [PERSON] et al. [142], the elastic distortion exerts a weak force (\(<\)5 \(k_{\text{B}}T\)) on neighbouring nanoparticles at a range of up to a few micrometres. Coupling the LC-mediated elastic interaction between nanoparticles with the long-range drag force exerted by the distortion gradient of director field, nanoparticle assemblies with ordered mesostructures in LCs are expected to be obtained, which will potentially be useful in applications connected with the fields of photonics and electronics [128; 254; 261; 263; 264; 315; 316; 317; 318; 319]. It has been reported that gold nanoparticles can be aligned along linear disclinations [316; 320] and trapped in the centre of toric focal conic defects of smectic phases [321].