Mesophases smectics

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. 

We took care in describing our approach more extensively. It shows clearly that here is a possibility to study how inter- and intramolecular properties in polymer systems with very different structures (mesophases, smectic polymers, melt) are interrelated. 

Formation of the Vi and V2 Mesophases and of the Non-Amphiphilic Cubic Mesophase "Smectic D . In Figures 1 and 5, the formation of the amphiphilic cubic mesophases Vi and V2 is attributed to transitional globular micellar forms which arise intermediate between the indefinitely extended fibrous (M) and lamellar (G) forms which constitute the middle and neat mesophases, respectively. With a few non-amphiphilic mesogens (19, 20, 21, 22) a cubic mesophase "smectic D is found intermediate in the thermal succession of mesophases between smectic A... 

FIG. 2.16 Schematic representation of the four main types of mesophases. Smectic with ordered (a) and unordered (a ) arrangement of the molecules in layers b) nematic c) cholesteric and d) discotic (from Plate and Shibaev (1987) Courtesy Plenum Press). 

II-6) (Table 6, entries 1 and 3). This indicates an enhanced stability, and consequently a higher state of order for the liquid crystalline phase. This is confirmed by the fact that polymers with a higher number of Z-double bonds (Table 6, entries 4 and 5) show a smectic mesophase. Smectic mesophases were also found in polymers with poly(acrylate) A, poly(methacrylate) B, poly(silox-ane) C, and poly(vinylcyclopropene) D backbones (Table 6 entries 13,15,17, 19). The isotropization temperatures of these polymers were approximately the same. 

Fig. 12 Schematic representation of the self-assembly of dendromesogens into various type of mesophases (smectic, hexagonal and rectangular columnar, micellar cubic, and tetragonal phases) by the control of the molecular shape conformation (from flat tapered to cylindrical to conical and to spherical shape). From [126]...

In general, the term liquid crystal is used to describe an intermediate phase between liquid and solid occurring in some organic compounds. The phase of liquid crystal can be divided into two mesophases smectic and nematic. Nematic liquid crystals can be further divided as chiral nematic or archiral nematic. In chiral nematic liquid crystals, sterol-related compounds are called cholesteric, and non-sterol-based compounds are termed chiral nematic. For heat transfer applications, encapsulated forms of chiral nematic [71] or the composite liquid crystal sheets of the cholesteric type [72] are commonly used. Recently, the application of micro-encapsulated liquid crystals has become more popular in heat transfer measurements because of the fast response and easy paintbrush or spray application to the test surface. 

The increase of ASj with m indicates that, for polymer molecules with longer aliphatic spacers, the conformations of these chains and the placement of the mesogenic units were increasingly more ordered for the mesophase (smectic) relative to the isotropic phase ... 

For the purpose of this article, we focus our attention on the nematic mesophase smectic orders are more crystal-like and thus are beyond our scope. Typical nematic liquid crystals are characterized by a uniaxial order, though imperfect, along the preferred axis of the domain. No such long-range order exists in directions transverse to the domain axis. In most examples, low molar mass (monomer) liquid crystals carry flexible tails. Conformational ordering of these tails in the mesophase has been extensively studied in relation to the odd-even character of the phase behavior with the number of constituent atoms of the pendant chain. Various statistical models and theories have been presented [52-57]. In most cases, however, the ordering of the tail is relatively weak [58,59]. 

As to the lateral L groups in (l.xix), even small ones usually perturb the structure of a mesophase and cause a significant depression in the clearing point. Moreover, they have a different effect on the thermal stability of the nematic and smectic mesophases. Smectic phases are much more infiuenced because lateral substituents strongly prevent side-by-side packing of rigid molecular cores favorable for the smectic ordering. 

Assigning the corresponding texture to the smectic mesophase is more difficult, due to the defects appearing in these mesophases. Smectic A mesophase may adopt a focal... 

Other more complex morphologies also arise for A-B mixtures. In particular, domains A and B may enclose each other, forming entangled networks, separated by a hyperbolic interface. Those cases include mesh , bicontinuous microemulsions, bicontinuous cubic phases and their disordered counterparts, sponge phases, which are discussed below. In these cases too, the sign (convex/concave) of the interfacial mean curvature sets the Type . A representation of the disordered mesostructure in a Type 2 bicontinuous microemulsion is shown in Figure 16.3. A hyperbolic interface may be equally concave and convex (a minimal surface, e.g. see Figure 16.2(c)) so that the mesophase is neither Type 1 nor Type 2. Lamellar mesophases ( smectics or neat phases) are the simplest examples. Bicontinuous balanced microemulsions, with equal polar and apolar volume fractions are further examples. 

Highly organized mesophase/ smectic-A (C), or highly organized mesophase/nematic 40... 

The simultaneous occurrence of nematic, cubic, layer and columnar structures in pure mesogens is of great importance to bridging the gap between calamitic and discotic molecules and the corresponding mesophases. Smectic, cubic and columnar phases have also been described in polycatenar compounds, and thus double-swallow-tailed mesogens can also be considered to be a special case of tetracatenar compounds (see Chap. XII of this volume). 

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