Thermotropic cubic

Cubic thermotropic liquid crystalline phases are designated Cub. 

B. Donnio, D. N. Bruce, H. Delacroix, T. Gulik-Krzywicki. Freeze-fracture electron microscopy of thermotropic cubic and columnar mesophases. Liq... 

Donnio, B., Garcia-Vazquez, P., Gallani, J.-L., Guillon, D. and Terazzi, E. (2007) Dendronized Ferromagnetic Gold Nanopartides Self-Organized in a Thermotropic Cubic Phase. Advanced Materials, 19, 3534-3539. 

The family of primary silver thiolate compounds AgSC H2n+1 ( = 4, 6, 8, 10, 12, 16, or 18), which in the solid state consists of 2x,[AgSR] layers, behaves as thermotropic liquid crystals. On heating, they display successively lamellar (smectic A), cubic, and micellar mesophases.969... 

Fig. 28. Self-assembling dendrons exhibiting a thermotropic cubic liquid crystalline phase reported by Percec et al. 

Note 4 Cubic mesophases have long been known in thermotropic salt-like compounds and in lyotropic liquid-crystals. 

Noted There are several types of thermotropic and lyotropic cubic mesophases, with different symmetry and miscibility properties when the space groups of these are known, they should be included in parentheses after the term Cub . 

Common cubic space groups in thermotropic LC systems Cuby laid, Imim (Pnim) Cubj Pmin, Imim. 

The cubic phase is a real curiosity in the study of thermotropic hquid crystals, although much has been done to unravel issues concerning its formation. Interested readers are directed to other sources for a detailed discussion (32) however, the phsise does crop up rather a lot in systems we have studied, so a brief introduction is in order. 

Figure 4.15 The structure of (a) complex [Gd(13)(N03)3 /2CH3CN /2H20 and (b) the head-to-tail stacking [29]. (Reprinted with permission from E. Terazzi, et al., Molecular control of macroscopic cubic, columnar, and lamellar organizations in luminescent lanthanide-containing thermotropic hquid crystals, Journal of the American Chemical Society, 127, no. 3, 888-903, 2005. 2005 American Chemical Society.)...

The cubic phase is still a rather rare observation in thermotropic liquid crystal systems, and is foimd in conventional calamitic materials, as well as in polycatenar materials vide infra). It is a viscous, optically isotropic phase whose kinetics of... 

As for low molecular weight surfactants, the superstructures are assumed to be formed by micellar aggregates [126], But it seems that the formation of lyotropic liquid crystals is supported by the additional presence of thermotropic mesogens [87,122-124,126], Lamellar, hexagonal, cubic and even nematic and cholesteric mesophases were reported for binary systems, the latter being exceptional. Lyotropic mesophases were also observed in non-aqueous solvents [240,400,401,405], If polymerizable surfactants are studied, not only the phase diagram but also the types of mesophases observed for the monomer and the polymer may be different. 

In the quest for a universal feature in the short-to-intermediate time orientational dynamics of thermotropic liquid crystals across the I-N transition, Chakrabarti et al. [115] investigated a model discotic system as well as a lattice system. As a representative discotic system, a system of oblate ellipsoids of revolution was chosen. These ellipsoids interact with each other via a modified form of the GB pair potential, GBDII, which was suggested for disc-like molecules by Bates and Luckhurst [116]. The parameterization, which was employed for the model discotic system, was k = 0.345, Kf = 0.2, /jl= 1, and v = 2. For the lattice system, the well-known Lebwohl-Lasher (LL) model was chosen [117]. In this model, the particles are assumed to have uniaxial symmetry and represented by three-dimensional spins, located at the sites of a simple cubic lattice, interacting through a pair potential of the form... 

C.J. Hawker and J.M.J. Fechet, Preparation of polymers with controlled molecular architecture. A new covergent approach to dendritic macromolecules, J. Am. Chem. Soc., 1990, 112, 7638 F. Zeng and S.C. Zimmerman, Dendrimers in supramolecular chemistry from molecular recognition to self-assembly, Chem. Rev., 1997, 97, 1681 D.J.P. Yeardley, G. Ungar, V. Percec, M.N. Holerca and G. Johnsson, Spherical supramolecular minidendrimers self-organized in an inverse micellar -like thermotropic body-centered cubic liquid crystalline phase, J. Am. Chem. Soc., 2000, 122, 1684. 

Mesophases can be locked into a polymer network by making use of polymerizable LCs [59]. These molecules contain moieties such as acryloyl, diacety-lenic, and diene. Self-organization and in situ photopolymerization under UV irradiation will provide ordered nanostmctured polymers maintaining the stable LC order over a wide temperature range. A number of thermotropic liquid crystalline phases, including the nematic and smectic mesophases, have been successfully applied to synthesize polymer networks. Polymerization of reactive lyotropic liquid crystals also have been employed for preparation of nanoporous polymeric materials [58, 60]. For the constmction of nanoporous membranes, lyotropics hexagonal or columnar, lamellar or smectic, and bicontinuous cubic phases have been used, polymerized, and utilized demonstrated in a variety of applications (Fig. 2.11). 

Disklike tetramer 38 of folic acid derivative containing oligo(glutamic acid) moieties has both thermotropic columnar and micellar cubic (Pm3n) phases [53-56]. By the addition of sodium salt, 38 forms supramolecular chiral structures in the columnar and cubic phases (Fig. 5.7). The formation of supramolecular chiral stmctures in the colunmar phase is due to the interactions between the hydrogen bonded disks and the ions [57, 58]. 

Vesicular LC phases are a new kind of LC phase with cellular structure that is formed by the spatial organization of cylindrical, spherical, or polyhedral aggregates of curved single layers, bilayers, or double layers. These phases have been considered as complicated columnar and cubic mesophases with core-shell morphology [192]. Till now only few vesicular mesophase are reported for thermotropic mesogens [193-196]. 

Therefore for thermotropic LCs, besides the usual columnar and micellar cubic LC phase, which can be considered as miceUar, vesicular LC structure are also... 

According to Fig. 3, classical thermotropic smectic phases of amphotropic liquid crystals are (SmA ), colunmar hexagonal (Col ), bicontinuous cubic (Cub, i), or discontinuous cubic (Cubjis) [169]. All these meso-phases include a disclination surface between the hydrophilic and the lipophilic parts of the unordered molecules. This surface can be uncurved (SmA), curved in one direction (columnar), curved in two directions with the same sign (discontinuous cubic), or curved in two directions with opposite sign (bicontinuous cubic). 

---