# Perspectives in Liquid-Crystal-Aided Nanotechnology and Nanoscience
## 1 Introduction
A fundamental investigation of the nanophysics of LCs was published by [PERSON] and [PERSON], who discussed a theory of magnetic nanoparticles suspended in a nematic LCs in 1970 [83]. Later in the same year, [PERSON] et al. reported the first suspension composed of nematic LCs and small magnetic particles [84]. The main idea of these pioneering studies was to control the director of the LC hosts by a coupling between LC molecules and elongated magnetic particles, producing what has been called magneto-nematics, i.e., nematic liquid crystals with ferromagnetic properties. In fact, it should be mentioned that this conclusion is wrong, as the produced system is not ferromagnetic. As the magnetic field is removed, the magnetization does in fact decrease to zero, while it should retain a finite value for ferromagnetics. Nevertheless, one could call the produced system an anisotropic ferrofluid. Still, this idea led the trend of studies on LC-nanomaterial suspensions for the next few decades. With the rapid development of composite LC materials, it was recognized that long-range orientation and interactions in mesophase can lead to a strong impact of nanomaterials on the properties of the LC hosts [85; 86; 87] and vice versa; the LC matrix can rearrange the orientational and positional order of nanomaterials [88; 89]. The coupling of long-range ordering in LCs and the unique properties of dopant nanomaterials allows us to change or even impose unique physical properties on the LC-nanomaterial composites by doping different kinds of nanomaterials in LCs [70]. Figure 3: **(a)** SEM image of a collection of tobacco mosaic virus particles. Scale bar: 0.2 \(\upmu\)m. Reproduced from Wikimedia Commons, with no author name supplied. **(b)** The orientational order parameter of the viruses increases as their concentration in the solvent is increased. Reproduced with permission from [46]. Copyright (1988) American Physical Society. Up to now, there have been four primary groups of nanomaterials used as dopants in LCs, i.e., metal nanoparticles, ferroelectric nanoparticles, semi-conductor nanoparticles, and carbon nanoparticles. Among these dispersions, improved physical characteristics and novel functionalities can be obtained depending on the physical and chemical characteristics of the dopants as well as the interaction between LCs and nanomaterials [90; 91; 92; 93; 94; 95]. For example, there are abundant reports declaring that doping metallic, semiconducting, oxide and ferroelectric nanoparticles into LCs can efficiently modify the electrical and mechanical (viscoelastic) properties of LC host, leading to large dielectric and optical anisotropy, low threshold voltage, and an improved electro-optical response [87; 92; 94; 96; 97]. In addition, ferroelectric nanoparticles can also increase the order parameter as well as the clearing point of the LC host due to the interaction between the elastic forces of LC molecules and the spontaneous polarization of ferroelectric nanoparticles [86; 98; 99; 100; 101]. Doping nematic LCs with ferromagnetic particles can effectively reorient the director of LCs by magnetic fields induced by the coupling of magnetic particles with LC molecules [83; 102; 103; 104; 105; 106]. At the same time, there have been reports claiming the exact opposite behaviour: an increase in threshold voltage, a slower optical response, and a decrease in order and in transition temperatures. This indicates that the properties of the composite materials are very much dependent on the dopant size, materials employed, preparation conditions and time. It further indicates that a lot more research is needed to fully understand these systems. With largely varying results, even on a qualitative basis, the field of liquid crystal nanoparticle composites is only in its infancy. Metal and semiconducting nanoparticles have been used to stabilise the mesophase known as the blue phase, effectively broadening the temperature range of this frustrated phase from 1 K to up to 20 K [107; 108].