Nematic domain

Many other interesting examples of spontaneous reflection symmetry breaking in macroscopic domains, driven by boundary conditions, have been described in LC systems. For example, it is well known that in polymer disperse LCs, where the LC sample is confined in small spherical droplets, chiral director structures are often observed, driven by minimization of surface and bulk elastic free energies.24 We have reported chiral domain structures, and indeed chiral electro-optic behavior, in cylindrical nematic domains surrounded by isotropic liquid (the molecules were achiral).25... 

FIG. 15.49 Orientation angle 6 between rodlike molecules, described by unit vector u and director n within one nematic domain of a macroscopically isotropic polydomain sample a denotes the size of the domain. From Beekmans, 1997. 

Chain rigidity can cause partial ordering of the macromolecules. While flexible macromolecules yield amorphous solutions and melts in which the individual coils interpenetrate each other, semiflexible macromolecular systems order in nematic domains [43],... 

Everett TA, Higgins DA (2009) Electrostatic self-assembly of ordered perylene-diimide/ polyelectrolyte nanofibers in fluidic devices from nematic domains to macroscopic alignment. Langmuir 25(22) 13045-13051... 

We have only described here the mineral mesophases that have been fully and unambiguously characterized. This review article is therefore not exhaustive. Other less well-documented examples can be found in the literature, in particular in another review article [127,128]. Nevertheless, the diversity of examples described here should draw the attention of the reader to the fact that suspensions based on anisotropic structural units may be liquid crystalline, a feature that could be used to obtain a better understanding/optimization of materials synthesis and processing conditions. Thus, the existence of a nematic domain in the phase diagram together with the possibility of growing reproducibly oriented single domains on the centimeter scale could be used, for instance, in the field of pillared materials to produce better structured materials. 

Fig. 2. Partial phase diagram of the binary mixture liquid crystal E7/silicone oil (Aldrich). is the E7 weight fraction. The Fig. shows an isotropic phase (1) above 60°C, a coexistence domain between an isotropic and a nematic phase (1+N) below 60°C, and a nematic phase (N) in the extreme right part of the diagram. The systems are quenched from the nematic domain to 20°C as indicated by the arrow...

Since the liquid crystal forms the continuous phase of the binary mixture, we are only interested in a small part of the total phase diagram. Weight fractions of the liquid crystal in the range 0.9 to 1 were used to determine the partial phase diagram of the mixture which is shown in Fig. 2. The system forms an isotropic (I) phase at high temperature, and a diphasic equilibrium between an isotropic and a nematic phase (N-i-I) at low temperature. A nematic domain (N) is found at intermediate temperatures and low silicone oil concentrations. As pointed out in the experimental section, the existence of this nematic domain has some importance prior to quenching the system to the diphasic region. The present mixture exhibits classical features usually observed in other mixtures of nematic liquid crystals and polymers or isotropic fluids [29,30]. 

Several mixtures with different silicone oil concentrations were prepared. Since the temperature quenches are performed from the nematic domain (N), the maximum weight fraction of silicone oil investigated was 0.035. When the sample is thermally quenched from the nematic domain (typically, 55°C) to the diphasic domain (20°C), the uniform single-phase mixture is thermodynami-... 

Lyotropic LCPs exhibit quite characteristic viscosity behavior in solution as the polymer concentration in solution is changed. Typically the viscosity follows the trend shown in Figure 5.6. As more and more polymer is added to the solvent, the viscosity increases while the solution remains isotropic and clear. At a critical concentration (which depends on the polymer and the solvent) the solution becomes opaque and anisotropic and there occurs a sharp fall in viscosity with further increase in the polymer concentration. This results from the formation of oriented nematic domains in which the chains are now aligned in the direction of flow, thereby reducing the frictional drag on the molecules. 

Windle and coworkers [51, 54, 56] have then interpreted some discrepancies between optical microstructures and X-ray diffraction patterns of nematic domains in copolyesters 3 and 6 in terms of biaxiality. 

II, rheooptics indicates systematic rotation of nematic domains hence, here these domains are dispersed in a continuous matrix. The latter structure dominates region... 

T-CNs film has a polydomain structure in which the helical axes of different chiral nematic domains point in different directions, with the pitch of each domain giving an average pitch. Because the pitch is related to the wavelength of maximum reflection of 2., by... 

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