Nematic LC host

From Gerber s model [21], the Kerr constant of a BPLC is determined by following LC parameters as  

The response time of a polymer-stabilized BPLC material is related to the LC parameters as [25]  

---

To improve the compatibility of GNPs in LC host, both of the simple n-alkyl thiol and LC/mesogen molecules are used simultaneously to form mixed mono-layer. For example, nematic cyanobiphenyl end-functionalized alkylene thiol covered GNPs and its mixing with n-alkyl thiols (n = 6, 12) in two cyanobiphenyl nematic LC hosts (5CB and 8CB) were investigated [60]. By adding small quantities of alkyl thiolate-capped GNPs there was effectively reversed nematic LC orientation which further showed opto-electronic responses [61]. Recently,... 

In recent years, scientists have developed various kinds of powerful photore-sponsive chiral dopants, and the stfategy using nematic LC hosts doped with photoresponsive chiral dopants currently is widely adopted for the investigation of photoresponsive CLCs [15-17],... 

Photoresponsive molecules are important for the fabrication and photomodulation of photoresponsive CLC materials, no matter if they are employed as chiral mesogens, achiral nematic LC hosts, or chiral/achiral guest molecules. The most important property of these molecules in photoresponsive CLC materials is the changes in molecular shape (geometry/conformation) as a result of the light-induced isomerization, which constitutes the basis for photomning of the properties of CLCs [18], The first example of using photoresponsive molecules to modulate the properties of CLCs was reported by Sackmann in 1971 [19], where azobenzene was employed as the dopant molecule. To date, various kinds of photoisomerizable molecules have been developed for this purpose (Fig. 5.3). 

FIGURE 5.5 Crossed polarized optical micrograph of the mixture of 25 wt% of 1 in an achiral nematic LC host 5CB on cooling at 38.9 °C (a) before UV irradiation (b) after UV irradiation for 10 s (c) 20 s after the removal of UV light at isotropic phase. Reprinted with permission from Reference 34. Copyright 2005 American Chemical Society. 

FIGURE 5.6 The structures of chiral diarylethene 2. Crossed polarized optical texture micrograph of 10 wt% of 2 in a nematic LC host 5CB at 42 (a) before irradiation (b) after UV... 

Li et al. reported two light-driven chiral molecular switches 36 and 37 with tetrahedral and axial chirality [116]. When chiral switch 36 was doped in nematic LC host E31 at 15 wt% concentration, phototuning the reflection color over the entire visible region was observed. An amazing feature of this photoresponsive CLC system is the quick relaxation. After 1 min of exposure to bright white light, it returned to... 

To widen BP temperature range, several approaches have been proposed [15-18] Here, we focus on the blue phases induced by incorporating chiral dopants into a nematic LC host. To make a polymer-stabilized blue phase liquid crystal, a small fraction of monomers (-8%) and photoinitiator (-0.5%) is added to the blue phase system. Figure 14.4 shows some exemplary nematic LC compounds, chiral dopants, and monomers [19]. Then we control the temperature within the narrow blue phase range to conduct UV curing. After UV irradiation, monomers are polymerized to form a polymer network, which stabilizes the blue phase lattice stmctures. 

In a polymer-stabilized self-assembled blue phase system, each material component plays an important role while interacting with the others. In the following, we will discuss the optimization of materials in terms of nematic LC host, chiral dopant, and monomers, respectively. 

Photochemically induced phase transition photochemical phase transition) of LCs in guest/host systems is interpreted as follows. 81 If a small population of photochromic compounds such as azobenzene are dispersed in nematic LCs (NLCs), the phase structure of the NLCs is susceptible to change induced by photochemical reac-... 

Recently, the importance of the structure of chiral metal complexes on the handedness of the mesophases induced in a nematic LC was exemplified [114]. The chiral metal complexes 10 and 11—in which the alkyl substituents are aligned almost perpendicularly to the C2 axis in the former and parallel in the latter—show very different induction phenomena. Not only are the induced helicities in the nematic LC of opposite sense for the two compounds, but the helical twisting power of 10 is much higher than that of 11. The reason for these differences is the way in which the molecules are incorporated into the host nematic phase and exert their force upon it to create the twist between the layers. 

In binary Ch LC systems consisting of the chiral compound and the host nematic LC, the intermolecular interaction between the chiral azobenzene molecule and LC molecule contributes to HTP of the chiral azobenzene compounds. In this section, photoswitching behavior of some chiral azobenzene compounds (Fig. 10.7) is examined in terms of the influence of the chiral groups on the photochemical change in HTP. 

The results of spectroscopic studies were reported for chain molecules such as n-alkanes or poly(oxyethylene) oligomers hosted in conventional nematic LCs. 

POM), the Schlieren and homeotropic defect textures of the nematic phase, and the focal conic and homeotropic defect textures of the smectic A phase could be observed (Fig. 4.3). In addition, the parallel and perpendicular dielectric permittivities of mixtures of the GNPs dispersed in host nematic LCs were determined by using one-cell method , which was reported by Clark et al. [47 9]. 

UV irradiation (Fig. 5.21). It is believed that the reversible handedness inversion originated from the conformation change of binapthyl moieties as well as the stereospecific intermolecular interactions between the binaphthyl moieties and the surrounding nematic LC molecules. This is the first example of diaryIthene dopant capable of handedness inversion in CLCs although it requires specific LC mixture host and only shows low HTPs. 

---