Smectic layer

Smectic mesophase that has a spacing between layers (smectic periodicity) of approximately one half of the molecular length. 

In any case, both models have in common that owing to the positional ordering of the mesogenic side chains, the polymer backbone no longer exhibits a statistical three dimensional coil conformation. Therefore at the phase transformation isotropic to smectic or nematic (cholesteric) to smectic, in addition to the change of the anisotropic packing of the side chains, the main chain has to change its conformation, which must be consistent with the layered smectic structure. A direct interaction... 

Rod-Like Liquid Crystals with One (Semi)Perfluorinated Chain Double Layer Smectic Phases... 

Layered Smectic Structure Mssogenic Units interacting... 

The poly(carbodiimide) 21 displays a specific rotation similar to the monomer. Solutions (20 %) of poly(N,N -di-n-hexylguanidine), using Cp-TiCl2NMe2 as catalyst in the polymerization reaction, form a layered smectic structure. ... 

There have been very few families of dendrimers built up around a pure siloxane core. One such dendrimer consisted of a dendritic methylsesquioxane matrix (Nq = 3, Mb = 2, Fig. 21) to which six terminal cholesteryl groups were attached via undecylene spacers [178]. This G1 compound exhibited a very broad temperature SmA phase (G -1.5 SmA 120 I). The molecules arrange in a single layer smectic phase with complete overlap of the cholesteryl meso-gens separated by siloxane layers. 

The chiral side chain polymers derived from asymmetric esters of terephthalic acid and hydroquinone can form (in a broad temperature range, including ambient temperature) an unusual mesophase (the isotropic smectic phase, IsoSm ) characterized by high transparency and optical isotropy within the visible wavelength range, combined with a hidden layered smectic ordering and some elements of helical superstructure at shorter dimensions of 10 to 250 nm. The short-pitch TGB A model seems to be the most adequate for the mesophase structure. 

The complexation of amphiphilic molecules with functionalized polymers forms layered smectic structures [94-97]. Polymeric complexes 41 consisting of poly(vinylpyridine) and an alkylphenol also form layered organized mesophases [94]. The incorporation of this structure into block copolymers with polystyrene results in the self-organization in two length scales, that is, block copolymer length and nanoscale length [95, 96]. 

Thermotropics may display various organized structures. The nematics (from the greek nematos=wire) are elongated cylinders which have one directional order and lie more or less parallel to one another (Fig.2b) Smectics are organized in layers where the director may have a variable orientation relative to that of the layer. Smectic A are perpendicular (Fig. 2c) and Smectic C tilted (Fig. 2d). The various structures of the layer lead to the distinction of 8 smectic phases (for details see Ref. 16-17). 

Fig. 30. The normal layered structure of the smectic A phase of a side chain liquid crystal polymer, and the proposed twisted structure of the layered smectic phase of a chiral side...

Our results also indicate that the melting point of PPBA increases with increasing extent of syndiotacticity. This supports the conclusion that a syndiotactic configuration favors the model previously proposed for the layered smectic structure. 

The pitch of the helix depends on concentration c of a dopant for small c Po ac and a is called helical twisting power of the dopant [15]. However, with increasing c the dependence becomes nonlinear and the heUx handedness can even change sign (the case of cholesteryl chloride dopant in p-butoxybenzyli-dene-p -butylaniline, BBBA, see Fig. 4.24). The same chiral, locally nematic phase with a short pitch in the range of 0.1-1 pm is traditionally called cholesteric phase because, at first, it has been found in cholesteryl esters. Such short-pitch phases manifest some properties of layered (smectic) phases. 

S. Jaradat, N. W. Roberts, Y. Wang, L. S. Hirst and H. F. Gleeson, Remarkably wide four-layer smectic phases in mixtures of liquid crystals and highly chiral dopants, J. Mater. Chem., 16, 3753-3761 (2006). 

The set of experimental data leads to the conclusion that complexes of MA and GA with the amine studied form layered smectic-like liquid crystalline phases within the certain temperature and concentration ranges. As concerned for the structure of the smectic layer it is necessary to analyze the value of the interplanar spacing d corresponding to the small angle X-ray reflection for both complexes of different composition. 

The best way to keep track of all these layered smectic and crystal phases is to use a chart listing the various phases along with a few of their most important properties. Figure 1.10 is such a chart. 

Figure 13 Structures of (a) nematic and (b) layered smectic A phases formed by dimesogens.

Different types of LC systems are found in elastomers. In nematic liquid crystals, the molecules have orientational but no positional order, their center of mass positions being randomly distributed. Most nematic elastomers are employed in uniaxial deformation. If the LC elements contain chiral groups, they are termed as cholesteric elastomers. Discotic nematic LC elastomers contain disk-shaped molecules that can be oriented in layers. Smectic LC elastomers form well-defined layers. 

Phases possessing only liquid-like short-range order within their layers smectic- (orthogonal) and C (tilted). 

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