Smectic B mesophase

Note 3 By contrast with a smectic B mesophase, a crystal B mesophase has correlations of positional order (hexagonal) in three dimensions, i.e., correlations of position occur within and between layers. 

Note 4 The structure of a smectic B mesophase is characterised by a D6h point group symmetry, in the Schoenflies notation, by virtue of the bond orientational order. 

Note 6 A smectic B mesophase is sometimes denoted SmBhex- The subscript hex denotes the hexagonal structure of the mesophase. 

Note 1 See Fig. 9a for an illustration of the molecular organization in a smectic F mesophase, a tilted analogue of the smectic B mesophase. 

Note 1 See Figs. 9(a) and (b) for illustrations of the molecular organizations of smectic F and I mesophases. They are tilted analogues of the smectic B mesophase. 

An even more dramatic example of the potential lack of selectivity afforded to the Norrish II reactions of ketones by supposedly very ordered systems than that described in the 76 systems is provided by neat samples of the mesomorphic alkanophenones (81) [278]. These molecules are capable of existing in nematic and smectic B mesophases (see Figure 16) as shown in Scheme 42. The instability of the monotropic smectic B phase of 81a and smectic B phase of 81b did not allow their photoreactions to be examined these smectic phases became solids soon after the initiation of irradiation. 

The positional order of the molecules within the smectic layers disappears when the smectic B phase is heated to the smectic A phase. Likewise, the one-dimensional positional order of the smectic M phase is lost in the transition to the nematic phase. AH of the transitions given in this example are reversible upon heating and cooling they are therefore enantiotropic. When a given Hquid crystal phase can only be obtained by changing the temperature in one direction (ie, the mesophase occurs below the soHd to isotropic Hquid transition due to supercooling), then it is monotropic. An example of this is the smectic A phase of cholesteryl nonanoate [1182-66-7] (4), which occurs only if the chiral nematic phase is cooled (21). The transitions are aH reversible as long as crystals of the soHd phase do not form. 

Thermotropic liquid-crystalline properties of different metal alkanesulfonates are studied by microscopy and X-ray diffraction [59]. Sodium soaps show smectic polymorphism of smectic A and smectic B phases. Ammonium soaps only show smectic A phases but polymorphism in the crystalline state. Calcium soaps show columnar mesophases. In Figs. 32 and 33 some textures and x-ray diffraction patterns are depicted. 

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. 

Figure 16.10 Conformational changes of polypropylene imine) dendrimers in LC materials from spherical to (a) cylindrical, in hexagonal columnar mesophase [130], and (b) ellipsoid, in smectic A mesophase [132]...

Note There are three types of hexatic smectic mesophases. smectic B (SmB), smectic F (SmF) and smectic I (SmI). Here, the term hexatic may be omitted because it is implicit for this group of smectic mesophases. 

A central part of the application-oriented evaluation of liquid crystals are so-called virtual clearing temperatures, electrooptic properties, and viscosities. These data are obtained by extrapolation from a standardized nematic host mixture. 7 Af, An, and jy are determined by linear extrapolation from a 10% iv/iv solution in the commercially available Merck mixture ZLI-4792 (Tfji = 92.8°C, Af = 5.27, An = 0.0964). For the pure substances the mesophases are identified by optical microscopy and the phase transition temperatures by differential scanning calorimetry (DSC). The transition temperatures in the tables are cited in °C, numbers in parentheses denote monotropic phase transitions which occur only on cooling the sample C = crystalline, S = smectic A, Sg = smectic B, S = smectic G, S> = unidentified smectic phase, N = nematic, I = isotropic. 

The same authors increased the complexity of their systems by introducing in a polyester chain both ionic and chiral chain segments. The series containing both the isosorbide chiral units and the ionic moieties yielded chiral smectic C (SmC ) and chiral smectic B (SmB ) liquid-crystalline phases, exhibiting broken focal-conic texture and schlieren texture. Not surprisingly, the analogous polymer without the chiral units exhibited only the nonchiral SmC mesophase. On the other hand, in this case, the effect of ionic units on the phase behavior was negligible [91]. 

Such a mobility does not exist in layered LC-main chain polymers (Fig. 1 IB). The mobility required for the definition and existence of a molten state results in LC-main-chain polymers exclusively from a gliding of chains along each other. Such a motion is only possible when the intermolecular forces between the mesogens are relatively weak. Therefore only smectic -A and smectic -C phases are true LC-phases. In contrast to small molecules smectic -B (and higher ordered smectic phases) are solid mesophases. The difference between a solid smectic mesophase and a smectic crystalline phase lies in the extent of the three dimensional order and is usually difficult to determine experimentally (see Sect. 7). 

Sm2Coi7 magnet swarf, 164f Smectic phases characterization, 10 smectic A phase (SmA), 10 11 smectic B phase (SmC), 11 smectic C phase (SmC), 10 11 Space filling mesophase, 7-9 Strontium(II) distribution ratio, 229f Structural properties of cerium... 

Figure 1.30 Different types of molecular organization (mesophases) which are cor observed (a) smectic, (b) nematic.

The initial stmcture of the as-spun CPE-1 fibers may be assumed as LC mesophase of the smectic B type. This system is then single-phase. Any... 

Among LC phases one distinguishes nematic phases with orientational ordering of the molecular long axes but irregular liquid-like positioning of the mass centers of the molecules (Fig. 2a) and numerous smectic phases with a layered structure. The simplest of them are smectic A, with the molecular axis normal to the layer plane, and smectic C, in which the molecular axes are tilted (Fig. 2b and c). Smectic phases A and C have short-range positional order within the layer, but layers of some other phases (e.g., smectic B) are more ordered. To date, about 20 smectic mesophases have been described, and 8 of them are tilted (smectics C, F, G, H, I,... 

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