Smectic C mesophase

Ballesteros, B., Coco, S. and Espinet, P. (2004) Mesomorphic Mixtures of Metal Isocyanide Complexes, Induding Smectic C Mesophases at room temperature and Liquid Crystalline Molecular Alloys . Chemistry of Materials, 16, 2062-2067. 

Note Two types of short-range smectic-like structures are possible. One is analogous to a smectic A mesophase where the molecules tend to lie along a layer normal and the other is like a smectic C mesophase where the molecules tend to be oblique with respect to a layer normal. See Fig. 2 for illustrations of the molecular arrangements in the smectic A type structure and the smectic C type structure. 

Note 2 The physical properties of a smectic C mesophase are those of a biaxial crystal. 

Note 4 The tilt direction varies in a random manner from layer to layer in conventional smectic C mesophases. However it can alternate from layer to layer, as in an antiferro-electric chiral smectic C mesophase (see Definition 5.9, Note 7) and in the smectic C mesophase formed by certain liquid crystal dimers with an odd-number of carbon atoms in the spacers. The recommended symbol for this type of mesophase is SmCa. 

Fig. 6. Illustrating the structure of the smectic C mesophase 3,1,5,1.3 chiral smectic C mesophase, (SmC )...

Smectic C mesophase in which the tilt direction of the director in each successive layer is rotated through a certain angle relative to the preceding one so that a helical structure of a constant pitch is formed. 

Note 1 See Fig. 7 for an illustration of the molecular organization in a chiral smectic C mesophase. 

Note 4 Locally, the structure of the chiral smectic C mesophase is essentially the same as that of the achiral smectic C mesophase except that there is a precession of the tilt direction about a single axis. It has the symmetry C2 in the Schoenflies notation. 

Smectic A and smectic C mesophases characterised by anti-parallel (SmA2, SmAj, and SmC2, SmCj) and random (SmAi and SmCi) alignments of the molecular dipoles within the layer thickness in Fig. 10. 

Note 1 Two forms of TGBC mesophase are possible in one form the director within the layer is tilted and rotates coherently through the layers in a block as in a chiral smectic C mesophase, while in the other form the director within a block is simply tilted with respect to the layer normal as in a smectic C mesophase. 

Note 6 Typical values of the spontaneous polarization, P, in chiral smectic C mesophases are between 10 and 10 " C m". ... 

Research utilizing the thiepine skeleton in material science has been reported. For example, liquid crystals with chiral dihydrodibenzo[c,i ]thiepines were studied. The enantiomerically pure (-)-(i )-3,9-bis[4-(dodecyloxy)benzoyl-oxy]-5,7-dihydro-l,l l-dimethyldibenzoR,f]thiepine 80 and (—)-(R)-3,9-bis[4-(dodecyloxy)benzoyloxy]-5,7-dihydro-1,1 l-dimethyldibenzoR,f]thiepine dioxide 82 display smectic C mesophases by a rigid twisted biphenyl core and axial chirality <1998JOC3895>. 

C - nematic mesophase sequence, and in the case of n=12 the tilt angle of the smectic C phases decreased with temperature, resulting in the formation of an additional smectic A phase [73]. The phase transitions of these polymers are given in Table 13. WAXD studies of poly-(XX-n), n=2-7 confirmed that these polymers had a nematic phase. Some additional structural features in the X-ray pattern were interpreted as smectic C fluctuations. Poly-(XX-8), however, showed a smectic C mesophase similar to those of poly-(XX-n), n=9-12 [74]. 

The monomers XXIV-m-n were crystalline solids and only the monomers with the shortest carbon-segments (n=4) showed an enantiotropic smectic C mesophase. Monomers with higher carbon chains did not exhibit a LC phase. 

The monomers XXIV-m-n were polymerized with initiator 4 in a monomer to initiator ratio of about 50. Table 16 summarizes the physico-chemical data for these polymers. Poly-(XXIV-m-n) exhibited smectic C mesophases, but these phases were only observed over a small temperature range and isotropization occurred shortly after the glass transition. It was not possible to identify the mesophase by polarized optical microscopy, but the smectic phase was confirmed by X-ray scattering experiments. Transition temperatures increased with the length of the carbon segments (n) but decreased with increasing siloxane segment (m). 

Reaction of a sodium alkoxydithiobenzoate with zinc acetate in dilute acetic add led to complexes of the empirical formula [Zn( -odtb)2]. The as-obtained materials were analytically pure, orange powders which showed a complex mesomorphism, apparently involving more than one species. However, crystallization yielded red crystals which had a well-defined mesomorphism, giving mainly nematic and some smectic C mesophases. 

P. Mach, R. Pindak, A.M. Levelut, P. Barois, H.T. Nguyen, H. Baltes, M. Hird, K. Toyne, A. Seed, J.W. Goodby, C.C. Huang and L. Furenlid, Structures of chiral smectic-C mesophases revealed by polarization-analyzed resonant X-ray scattering, Phys. Rev. E 60(6), 6793-6802, (1999). 

More recently, it has been theoretically predicted by Brand [81] that elastomeric networks that have chiral nematic or smectic C mesophases should have piezoelectric properties. The non-centro-symmetric material responds to the deformation via a piezoelectric response. Following this prediction, both Finkelmann and Zental have reported the observation of piezoelectricity. In one case, a nematic network was converted to the cholesteric form with the addition of CB15, 2 -(2-methylbutyl)biphenyl-4-carbonitrile [82]. By producing a monodomain, it is possible to measure the electro-mechanical or piezoelectric response. Compression leads to a piezoelectric coefficient parallel to the helical axis. Elongation leads to the perpendicular piezoelectric response. As another example, a network with a chiral smectic C phase that possesses ferroelectric properties can also act as a piezoelectric element [83]. Larger values of this response might be observed if crosslinked in the Sc state. 

Polyester homopolymer C5C10, structurally analogous to the main-ch block, formed nematic and smectic C mesophases (8,9). Within each series, the block copolymers are designated with a letter from a to d referring to the different amount of the methacrylate monomer present in the feed mixture. 

An example of molecules which form a polymeric chiral smectic C mesophase is a comb-like polymethacrylate (l.xii)... 

The sense of the pitch of the chiral smectic C mesophase is controlled by the same molecular factors as that of the cholesteric phase. If a chiral nematic forms a tilted smectic phase (C, H, I ) on cooling, either directly or through an intermediate smectic A phase, the smectic phase has the same sense of rotation as the chiral nematic phase. 

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