# Perspectives in Liquid-Crystal-Aided Nanotechnology and Nanoscience
## 1 Introduction
Silica, ferroelectric and metal nanoparticles can effectively influence the electro-optical response of nematic LCs and induce a memory effect, i.e., a residual transmittance can be maintained without external electric fields being applied [109; 110; 111; 112]. Moreover, a frequency-dependent electro-optical response can be obtained in suspensions of metal nanoparticles and nematic LCs due to the coupling of the dielectric properties of the nanoparticles and the LCs [78; 113]. It was also reported that carbon nanotubes dispersed in nematic LCs would align along the direction of the LC director, therefore largely changing the conductivity depending on the orientation of the tubes [114]. In fact, it could be shown that the nanotubes can be reoriented elastically by reorienting the director through applied electric or magnetic fields. Fullerenes could effectively improve the switching speed of a nematic host LC [95], and improved electro-optic responses could be induced by doping graphene oxides in LCs [115]. In addition to changing the intrinsic physical properties of the pristine LC materials mentioned above, intriguing photonic functionalities can also be introduced into the composites by combining nanomaterials with LCs, which is considered a promising method for the building of novel metamaterials [116]. Metamaterials are artificial engineered bulks with regular nanostructures that show exotic optical properties [117]. Combining the emerging field of optical metamaterials with LCs provides an extremely attractive quality, i.e., tunability, which is of the utmost importance in applications such as optically addressed spatial light modulators, tunable photonic materials and dynamic holography [118; 119; 120]. When integrating LCs with metamaterials, one can modify the director alignment of LCs by applying external stimuli and therefore manipulating the overall optical characteristics of the composite [119]. For instance, upon periodically embedding particular metal nanomaterials, such as gold nanoparticles, into LC matrixes, a localized surface plasmon resonance (LSPR) will be obtained, which can be tuned by adjusting the birefringence of the surrounding LC matrix [77; 81; 121; 122; 123; 124; 125]. Apart from the abovementioned technologies, novel photonic properties and applications can be further exploited for nanodopants including semiconducting nanomaterials, dyes, oxides, quantum dots (QDs), etc. [126; 127; 128; 129]. Instead of the SPR effect in the metallic nanomaterial-LC colloidal systems, the main property of interest in these cases is photoluminescence. The optical excitation and emission of these nanomaterials could be tuned effectively through the interaction between nanomaterials and the long-range ordered LC molecules, leading to a series of potential applications such as information storage, displays, LC lasers, etc. [130; 131; 132; 133; 134]. At present, one of the central challenges faced by the development of novel LC-nanomaterial composites is reliable assembly of nanoscale building blocks into functional bulk materials by using distorted LCs. It has already been demonstrated that the localisation of a nanoparticle in a distorted LC region allows the decrease of the free energy, and the directional motion of nanomaterials in LCs can be driven by the collective long-range interactions mediated by the LC director field. As a result, the energetic cost of LC defects enables them to entrap and reorient nanomaterials in a reversible manner and with well-manipulated position and orientation [135; 136; 137; 138]. In addition, nanomaterials that are suspended in LCs and have a given anchoring energy at the surface will induce a deformation of the orientation in the surrounding LCs, producing topological defects in the vicinity of the nanoparticle. The elastic distortion exerts a force on neighbouring nanomaterials at a range of up to a few micrometres, resulting in defect lines or points around nanomaterials [139; 140; 141; 142; 143; 144].