Smectic E phases

Fig. 11 Binary phase diagram between phthalic acid and decyloxystilbazole. (Crc and Cra are the crystal phase of the complex and the acid, respectively E is the crystal smectic E phase). Adapted from [35]...

The crystal smectic phases differ from those already discussed in that the layers are rather well correlated. The crystal smectic E phase is an orthogonal, orthorhombic phase. 

To summarize our results on side-chain all-hydrocarbon LC polymers [I], we found that they displayed Smectic E phases at lower temperatures and Smectic B phases at higher temperatures. The corresponding LC monomers exhibited only Smectic B phases. The presence of tails seems to enhance and stabilize liquid crystallinity. The monomers and polymers that do not have tails are not liquid crystalline. All of the substituted biphenyl hydrocarbon liquid crystals found in the literature are disubstituted. Examples of monosubstituted biphenyl hydrocarbon liquid crystals have not been found. The results obtained from this work support the idea that disubstitution of the biphenyl moiety is necessary to obtain a liquid crystalline phase. 

Abbreviations K = crystalline phase. D = columnar phase, Sh = smectic B phase. = smectic E phase. S.-N - nematic phase. I = isotropic fluid, Tj = thermal decomposition. aa and a/ refer to isomers of porphyrin. 

In the meantime, Ohta et studied the complete series of symmetric copper complexes ((53) M = Cu R = R = C H2 +i, = 0 to 14), which confirmed the previous results. The ligand showed a crystal smectic E phase from the octyl derivative onwards as determined by miscibility studies. The first four complexes ((53) M = Cu R = R = C H2 +i, = 0 to 3) were not mesomorphic, then a mono tropic phase was detected for = 4, which became enantiotropic for > 5. Moreover, for n = l and 8, the copper complexes showed an additional mesophase, while the nonyl derivative exhibited two additional mesophases. Crystalline structures of some tetra-alkyl copper, palladium, and nickel complexes of / -diketonates revealed that the flat molecular species were stacked into columns, the planes of the molecules forming a small tilt with respect to the columnar axis-these columns were further organized into layers. Variable-temperature and NMR ... 

Cr, crystalline phase SmA, smectic A phase SmE, smectic E phase SmX, unidentified smectic phase Colh, hexagonal columnar phase I, isotropic liquid. > > ... 

Such an assignment is, however in conflict with that made by Van Luyen and Strzelecki who reported the poly(, i -diphenylsebacate) to be nematic. X-ray patterns of oriented specimens will be necessary to substantiate the nature of this mesophase. Bosio et al reported from texture observations that the lower homologues in series XVI may exhibit a 3-dimensional ordered smectic E phase in addition to 2 D-liquid smectic A and nematic phases. At low temperature, the inner sharp diffraction ring and the four sharp outer rings are consistent with the formation of such a highly ordered mesophase. 

Fig. 5.26 Smectic E phase. The herringbone structure (a) and corresponding diffraction pattern (b) for two different directions of scattering, parallel ( n) and perpendicular ( x) to the director. As an example, the two Miller indices are shown only for qn. They mark Bragg reflections of the first and second orders from the horizontal crystallographic planes...

Smectic E Se- Although the smectic E phase may occur on its own or in conjunction with a higher temperature nematic phase, it is most commonly encountered in the sequence of phases N Sa Sb Se, where the arrows indicate decreasing temperature. 

Other smectic phases. Other smectic phases have been observed, where each phase relates to a particular type of crystal structure as defined in Chapter 2. For instance, smectic D is associated with a disordered cubic structure, smectic FI appears to be a tilted smectic B phase and the smectic G phase has close similarities with the smectic E phase but is tilted. A list of smectic phases is presented in Table 3.1. 

The smectic E phase, as shown by experiment, is optically biaxial but the molecules are arranged orthogonally to the plane of the layer, de Vries [Ic] assigns to this plane a two-dimensional structure which corresponds to the orthorhombic lattice. As in the Be phase the arrangement of the molecules in neighboring smectic layers is correlated. 

Vaz NA, Vaz MJ, Doane JW (1984) Molecular ordering and motion within the smectic-E phase - NMR-study. Phys Rev A 30 1008-1016... 

Monomer B5A exhibits two enantiotropic smectic mesomorphic phases (Se66Sb75I). The S phase does not crystallize even when cooled down to -20 "C. In this study, we will concentrate on the photopolymerization of B5A at room temperature (Sg phase) and the detailed structural characterization of the resulting polymeric network (subsequently called PB5A-RT). The synthesis and structural characterization for monomer B5A will be presented in a separate paper and only summarized results are presented here for comparison with its polymer. Monomer B5A in the smectic E phase has an orthorhombic structure with unit cell dimensions, a=6.609 A, b=7.704 A and c=51.92 A. It adopts a tilted molecular bilayer structure within the unit cell in the c direction. Within each smectic layer the molecules are tilted, making an angle of about SO with the smectic layer normal (or c direction). 

Twins possibly occur in liquid crystals that have a structure close to that of solid crystals, with more or less extended three-dimensional order, possibly in a smectic E phase (see Sec. 7.4.4.6). 

Another approach, utilizing the intensities of layer reflections from both X-ray and neutron diffraction experiments to obtain estimates for has been applied to the SmA, SmB and smectic E phases of IBP-BAC[126]. 

The first evidence for incommensurate smectic modulations was obtained by Leadbetter and coworkers in the smectic E phase of n-alkyl cyanoterphenyls [181, 182]. Subsequent studies presented evidence for fluid SmAi SmA2,i c and SmAinc soliton phases in binary mixtures [183-185]. However, more recent high resolution X-ray studies have contradicted these latter findings and have found that the apparently incommensurate phases are actually coexistence regions between various smectic phases (e.g. SmAi-bSmA SmA2 + SmAd) [24, 186-189]. These authors have recently claimed to have found a true incommensurate ordered smectic phase in mixtures of TBBA and DB6 [190]. Evidence has also been presented for two soli-ton-type incommensurate SmA phases (one... 

The polymeric SmB phase appears to be a stacked hexatic phase, although this cannot be confirmed until a true monodomain (rather than a fiber-averaged) sample becomes available for X-ray study [26]. Interestingly, in the polymeric smectic E phase, unlike that in molar mass systems, the adjacent smectic layers appear to be uncorrelated [362-364]. 

Various types of evidence lend support to the conclusion that poly(terphenyl-4,4" dicarboxylates) with short flexible spacers form a smectic E phase in addition to smectic A and nematic phases. Cooling of the smectic A phase produced a phase which showed a simple fan texture. The fans were lightly chequered and some arcs ran laterally across them as in a transient fan-shaped texture of smectic At low temperature, the... 

Funahashi, M., Zhang, F., Tamaoki, N., Hanna, J. Ambipolar transport in the smectic E phase of 2-propyl-5//-hexynylterthiophene derivative over a wide temperature range. ChemPhysChem 9, 1465-1473 (2008)... 

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