# Perspectives in Liquid-Crystal-Aided Nanotechnology and Nanoscience
## 4 LC-Aided-Assembly and Self-Assembly of Nanomaterials
Apart from this, the alignment and assembly of CNTs in traditional thermotropic LCs [2; 328; 329; 330; 331] and macromolecular LCs [332; 333] have also been reported. Apart from the relatively simple one- (organized by nematics, smectics and cholesterics) and two- (columnar phases) dimensional nanoparticle structures, the structurally rich world of LCs also provides phases with complicated spatial modulation of density and molecular orientation, periodic in three (blue and cubic phases) dimensions [334]. As a distinct class of frustrated phases, Blue Phases (BPs) are composed of double-twist cylinders, energetically favoured at high enough molecular chirality, but always leading to geometric frustration since it is impossible to tile the whole 3D space with double-twist cylinders without introducing disclination lines. These disclination lines either self-assemble into a 3D periodic regular lattice (BPI and BPII) or remain amorphously distorted (BPIII), which make BPs potential candidates for the 3D template of trapping sites for nanoparticles [335]. According to the computer simulations of [PERSON] et al. [318], nanoparticle-BPLC composites can give rise to regular crystals, glasses, percolating gels, isolated clusters, twisted rings and undulating colloidal ropes (Figure 13a). The wide variety of structures can be tuned via the concentration and anchoring condition of particles as well as external stimuli. Such a new class of composites will be promising for switchable, multistable devices for optical technologies such as smart glass and e-paper. Furthermore, particle trapping can also substantially increase the thermal stability range of the blue phase, by a factor of two or more [107; 108; 336] (Figure 13b). Apart from the disclinations in BPs, other defects such as focal conic domains in smectic LCs [321], fingerprint textures in CLCs [337; 338; 339], or even the LC-water interface [340], as well as the topological defects induced by microparticles [311], can also be used to trap nanoparticles and produce periodic arrays. On the other hand, it is well known that 1D or 2D anisotropic nanoparticles, such as CNTs and GOs, can act as LC building blocks in isotropic solvents and will entropically form lyotropic liquid crystalline phases above a critical volume fraction due to the excluded volume interactions, according to [PERSON]'s theory. According to the simple steric model, the molecular configurations are dominated by steric effects, which are dependent on the molecule concentration. In a dilute solution, the molecular configuration behaves isotropically due to the large free volume. In a condensed solution, the free volume is inhibited by the concentrated inclusions and, as a consequence, the suspension becomes  
Figure 13: (**a**) Snapshots of the steady states obtained when a dispersion of colloids with different concentration in the isotropic phase is placed in a sandwich geometry and then quenched into a regime where BP I is stable in the bulk. Reproduced with kind permission from [318]. Copyright (2014) Springer Nature. (**b**) The phase diagram for the BPLC/nanoparticle composite. Reproduced with permission from [336]. Copyright (2018) Optical Society of America. liquid crystalline. In such suspensions, the nanoparticles exhibit the long-range orientational order with the thermodynamic stability [341]. Such nanoparticle LCs are particularly interesting and hold great potential in industrial applications such as thin films, fibres and various multifunctional composites. A variety of different materials have recently been studied to an increasing extent, such as carbon nanotubes, graphene oxide, nanorods and nanowires, viruses, clays and nanocrystalline cellulose. Because of their anisotropic shape, CNTs may form lyotropic nematic LC phases when they are suspended in an isotropic liquid medium at a sufficiently high concentration [342; 343; 344].