Chiral smectic C SmC

The same authors increased the complexity of their systems by introducing in a polyester chain both ionic and chiral chain segments. The series containing both the isosorbide chiral units and the ionic moieties yielded chiral smectic C (SmC ) and chiral smectic B (SmB ) liquid-crystalline phases, exhibiting broken focal-conic texture and schlieren texture. Not surprisingly, the analogous polymer without the chiral units exhibited only the nonchiral SmC mesophase. On the other hand, in this case, the effect of ionic units on the phase behavior was negligible [91]. 

Chemical modification of the polymer structure allows the obtention of nematic and smectic phases [4, 5]. If the side group and/or the chain are chiral, then cholesteric or chiral smectic C (SmC) phases can be obtained. These can also be obtained by mixing a chiral compound with the SCLCP. SmC SCLCPs are of particular interest and their behavior is described in Sec. 2 of this Chapter. 

The reports on photoresponsive chiral LCs can be traced back to the 1960s and 1970s, during which a number of examples on photomning of pitch length in cholesteric phases were demonstrated [5-7]. To date, numerous reports have been found to be related to their physics, chemistry and applications. This chapter mainly deals with the recent progress in this area with a survey of three major classes of chiral LC phases, i.e. cholesteric (N ), chiral smectic C (SmC ) and blue phase (BP) from their stmctures to properties and applications. 

The precursor 6 exhibits the enantiotropic nature of chiral nematic (N ), chiral smectic C (SmC ) and chiral smectic I (SmI ) phases. The shell-printed texture of the SmC phase and the rose-like texture of the SmI phase can be clearly seen in Figure 12.6. The thiophene monomers, M2 and M3, show enantiotropic N, SmA and SmC phases. The SmC phase is characteristic of ferroelectricity. The polymers show various mesophases. The phase transition temperatures are summarized in Table 12.4. PI shows an enantiotropic SmA phase. P2 shows enantiotropic SmA, SmC and SmB phases. The fan-shaped texture of the SmA phase and the striated fan-shaped texture of the SmC phase are shown in Figure 12.7. P3 shows an SmA phase in the heating process and SmA and SmX phases in the cooling process. XRD analysis suggests that the SmX phase of P3 might be a higher order smectic phase. 

Figure 12.6 Polarizing optical micrographs of compound 6. (a) Shell-printed texture of chiral smectic C (SmC ) phase at W4°C (b) rose-like texture of chiral smectic I (SmI ) phase at 91 °C. From H. Narihiro, X.-hA. Dai, H. Goto, K. Akagi, Synthesis and properties of polythienylene derivatives with fluorine-containing chiral liquid crystalline substituents (I), Mol. Cryst. Liq. Cryst, 365, 363-371 (2001), reprinted by permission of the publisher (Taylor Francis Ltd, http //www.tandf.co.uk/journals)...

The phase transitions starting from the smectic phase were also observed in several doped systems [57-60]. The smectic LC host 8CB, doped with chiral molecules and azobenzene compounds, showed the phase transition from smectic to cholesteric due to the photo-induced isomerization of azobenzene molecules, and the prolonged irradiation drove the phase transition further to the isotropic phase. Matsui et al. also reported a chiral smectic C (SmC )-cholesteric (N ) phase sequence in azo-dye-doped ferroelectric LCs [57]. 

In this thesis a lyotropic analog of the thermotropic chiral smectic C (SmC ) phase is presented for the first time. So far, only very scarce examples of the achiral variant of this phase have been known in lyotropic liquid crystals and no comprehensive studies have been performed on them. Thus, the focus of the present thesis is on the proof of existence and characterization of this novel phase. Furthermore, a tentative model of the lyotropic SmC analog phase is introduced. Thereby, this thesis contributes to the unification of the often separately treated fields of lyotropic and thermotropic liquid crystals. 

The plethora of liquid crystal structures and phases is categorized into two main classes thermotropic and lyotropic liquid crystals. While thermotropic liquid crystals are formed by, e.g., rod- or disc-shaped molecules in a certain temperature range, lyotropic liquid crystals are liquid crystalline solutions, built up by, e.g., aggregates of amphiphilic molecules in a certain concentration range. Many liquid crystal phases are found in thermotropic as well as in lyotropic systems. In some cases, however, the lyotropic analog of a thermotropic phase has never been observed. The probably most interesting of these missing link cases is the thermotropic chiral smectic C (SmC ) phase, which has become famous as the only spontaneously polarized, ferroelectric fluid in nature. 

The chiral smectic C (SmC ) phase is well known as a liquid crystal phase that is ferroelectric. Smectic A (SmA) and smectic C (SmC) are the fundamental smectic liquid crystal phases. As shown in Fig. 5.1.1, the director n is parallel to the smectic layer normal z in the SmA phase and it is an optically and dielectrically uniaxial... 

Figure 1.14. Symmetry elements of the nonchiral smectic-C (SmC) phase (point group C2a), and the chiral smectic-C (SmC ) phase (point group C2). For both phases, the rotation around the C2-axis by n transforms a hypothetical polarization P = Px,Py,Pz) into —Px,Py,—Pz)- Therefore, P and P must be zero due to the symmetry of these phases. The additional symmetry element cr/, in the SmC phase transforms Px, Py, Pz) into Px, —Py, Pz), so that Py — Q m SmC. However, the same...

The typical hysteresis curve and the proposed director structure of the antiferroelectric chiral smectic C (SmC ) phase. 

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