Biaxial smectic

Using this method, the M6R8/PM6R8 blend showed precisely the behavior expected for the achiral SmAPA structure. Specifically, the optical properties of the films were consistent with a biaxial smectic structure (i.e., two different refractive indices in the layer plane). The thickness of the films was quantized in units of one bilayer. Upon application of an electric field, it was seen that films with an even number of bilayers behaved in a nonpolar way, while films with an odd number of bilayers responded strongly to the field, showing that they must possess net spontaneous polarization. Note that the electric fields in this experiment are not strong enough to switch an antiferroelectric to a ferroelectric state. Reorientation of the polarization field (and director structure) of the polar film in the presence of a field can easily be seen, however. 

Y. Wang, H. Yoon, H.K. Bisoyi, S. Kumar, Q. Li, Hybrid rod-like and bent-core liquid crystal dimers exhibiting biaxial smectic-A and nematic phases. J. Mater. Chem. 22, 20363-20367 (2012)... 

Semmler, K. J. Dingemans, T. J. Samulski, E. T. Biaxial smectic phases in non-linear optical properties and phase behaviour of an oxadiazole liquid crystal. Liq. Cryst. 1998, 24, 799-803. 

Eremin, A. Diele, S. PeM, G. Nadasi, H. Weissflog, W. Salfetnikova, J. Kresse, H. Experimental evidence for an achiral orthogonal biaxial smectic phase without in-plane order exhibiting antiferroelectric switching behavior. Phys. Rev. E. 2001,64,051707. 

Sadashiva, B. K. Reddy, R. A. Pratibha, R. Madhusudana, N. V. Biaxial smectic A liquid crystal in a pure compound. Chem. Commun. 2001, 2140-2141. 

Fig. 5.2. Schematic idealized pictures of calamitic mesogen supramolecular organization in (a) uniaxial nematic (N), (b) uniaxial smectic-A (Sa), and (c) biaxial smectic-C (Sc) with an average tilt a depicted in the layers conservation of the tilt direction from layer to layer is called a syncUnic stacking motif.

Results for biaxial smectics and columnar phases have additional compressional terms, but tilted smectic phases can support additional torsional distortions. Such phases are conveniently described in terms of two directors, one along the tilt direction, corresponding to the nematic director n, and the projection of n on the layer plane, known as the c-director (see Fig. 6). 

The description of the elastic properties of columnar phases, biaxial smectics, chiral... 

Torsional distortions can now be written in terms of derivatives of a and c, and it is found [10] that nine torsional elastic constants are required for the smectic C phase. Mention should be made of the biaxial smectic C phase, which has a twist axis along the normal to the smectic layers. This helix is associated with a twist in the c-di-rector, and so elastic strain energy associated with this can be described by terms similar to those evaluated for the chiral nematic phase. 

In fact, two new representatives of polar achiral systems have been discovered quite recently antiferroelectric polymer-monomer mixtures [286] and ferroelectric biaxial smectic A phases composed of ba-nana-like molecules [287]. 

Upon cooling from the isotropic melt, compound 1 forms a smectic A phase at 194 °C, followed by an unidentified biaxial smectic X phase at 141 °C. On the other hand, the equimolar mixture and D-glucamine and PPY did not show liquid crystallinity. The layer spacing of the smectic phase of compound 1 decreases with decreasing temperature from 4.9 to 4.3 nm in the SmA phase. The SmX phase has a layer spacing of 5.5 nm. The molecular length is estimated to be about 3.7 nm and Fig. 11.30 shows the layer structure model of the SmX and SmA phases. 

Recent optical experiments have probed the effect of flexible polymeric solutes in both lyotropic [36] and thermotropic liquid-crystal [37, 38] environments. Long-chain solutes feel an average effective anisotropy, and are found to exhibit much stronger ordering than smaller solutes. The synthesis of the bent-core mesogens ( banana molecules) has resulted in a novel biaxial smectic-A (both pure phase [39] and solute-induced [40]) as well as nematic phases [41,42]. 

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