Smectic G phase

Dialkylphenylbithiophene derivative 24 exhibits a smectic G phase between 140 °C and 225 °C. In the smectic G phase, high electron mobility of up to 0.07 cm2 V-1 s-1 as well as a high hole mobility of 0.044 cm2 V-1 s-1 is observed using the time-of-flight method [107]. Kreouzis and coworkers... 

The principal difference observed between the derivative with a racemic sulphoxide and that with the enantiopure form, (7 )-(6.20) or ( )-(6.20), is in the thermal behaviour. The (rac)-(6.20) compound exhibits a smectic G phase, followed at higher temperature by smectic F, while the enantiopure compounds show only a smectic F. The melting point of the enantiopure compounds is 10 K higher than the corresponding racemic compound. 

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. 

Imine-derived dinuclear palladacycles being ligated by amido or dialkyldithiocarbamato ligands show liquid crystal behavior and nematic smectic A and smectic G phases. " Other derivatives being OH-, hydroxo-amido-, amido-thiolato, or amido-carbxylato-bridged have also been prepared. The solution behavior, kinetics and mechanism of the acid-catalyzed cyclopalladation of imines, that is, A-benzylidenebenzylamines, -anilines, and -propylamine with Pd(OAc)2 in acetic acid has been studied. G-H electrophilic bond activation occurs to produce different types of metallacycles. 

Garland C W and Nounesis G 1994 Critical behavior at nematic-smectic-A phase transitions Phys. Rev. E 49 2964-71... 

Leadbetter A J 1979 Structural studies of nematic, smectic A and smectic C phases The Moiecuiar Physics of Liquid Crystais ed G R Luckhurst and G W Gray (London Academic)... 

Thus the formation of tilted analogues of the smectic A phases, i.e. monolayer Cl and bilayer C2, is possible for mesogens with relatively large electric quadrupoles. In the case of strongly sterically asymmetric molecules (e.g., zigzag shaped or dumbell shaped molecules, Fig. 3b) these quadrupolar interactions may be steric in origin. From this point of view observation of molecular tilt in the molecular dynamics simulations for a one-layer film of DOBAMBC in the absence of electrostatic interactions is not so surprising [106]. 

This work was extended to include acetylides (alkynyls) of the type (RNG)Au-G=C-C6H4-/)-C H2 +1, with n — 6-12 (even numbers), and R as above. The compounds were prepared from (tht)AuCl and the alkynes /)-HC=C-C6H4-C H2 +1 in aqueous acetone with soda as a weak base. The resulting insoluble, polymeric alkynylgold(i) complexes were dissolved in an organic solvent by adding equivalent quantities of the isocyanides. All products show distinct transitions from a crystalline to a smectic A phase and finally to the isotropic melts.206... 

Cr Cub, Cubv d E G HT Iso Isore l LamN LaniSm/col Lamsm/dis LC LT M N/N Rp Rh Rsi SmA Crystalline solid Spheroidic (micellar) cubic phase Bicontinuous cubic phase Layer periodicity Crystalline E phase Glassy state High temperature phase Isotropic liquid Re-entrant isotropic phase Molecular length Laminated nematic phase Correlated laminated smectic phase Non-correlated laminated smectic phase Liquid crystal/Liquid crystalline Low temperature phase Unknown mesophase Nematic phase/Chiral nematic Phase Perfluoroalkyl chain Alkyl chain Carbosilane chain Smectic A phase (nontilted smectic phase)... 

Sigaud G, Hardouin F, Achard MF, Levelut AM (1981) A new type of smectic A phase with long range modulation in the layers. J Phys (Paris) 42 107-111... 

In the framework of irreversible thermodynamics (compare, for example, [31, 32]) the macroscopic variables of a system can be divided into those due to conservation laws (here mass density p, momentum density g = pv with the velocity field v and energy density e) and those reflecting a spontaneously broken continuous symmetry (here the layer displacement u characterizes the broken translational symmetry parallel to the layer normal). For a smectic A liquid crystal the director h of the underlying nematic order is assumed to be parallel to the layer normal p. So far, only in the vicinity of a nematic-smectic A phase transition has a finite angle between h and p been shown to be of physical interest [33],... 

To extract concrete predictions for experimental parameters from our calculations is a non-trivial task, because neither the energetic constant B nor the rotational viscosity yi are used for the hydrodynamic description of the smectic A phase (but play an important role in our model). Therefore, we rely here on measurements in the vicinity of the nematic-smectic A phase transition. Measurements on LMW liquid crystals made by Litster [33] in the vicinity of the nematic-smectic A transition indicate that B is approximately one order of magnitude less than Bo. As for j we could not find any measurements which would allow an estimate of its value in the smectic A phase. In the nematic phase y increases drastically towards the nematic-smectic A transition (see, e.g., [51]). Numerical simulations on a molecular scale are also a promising approach to determine these constants [52],... 

Most of the compounds (96-105) collated in Table 3.9 exhibit a nematic phase as well as an unwanted smectic B phase. However, only the compounds linked directly, e.g. (96-99,102 and or linked by the... 

Chiral lc-polymers can be prepared by a proper functionalization of lc-polymers with chiral and reactive groups. These elastomers are interesting, because they combine the mechanical orientability of achiral lc-elastomers with the properties of chiral lc-phases, e.g. the ferroelectric properties of the chiral smectic C phase. The synthesis of these elastomers was very complicated so far, but the use of lc-polymers, which are functionalized with hydroxyl-groups, has opened an easy access to these systems. Also photocrosslinkable chiral lc-polymers can be prepared via this route. 

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. 

Complexes of Rh(I) and lr(I) are readily obtained from [M2(//-COD)2( r -Cl)2] (COD = 1,5-cyclooctadiene) and are examples of simple, dipolar mesogens [37]. Complexation led to mesogens which showed nematic and smectic A phases whose stability was very much greater than that of the ligand (e. g. clearing point for the Rh complexes was mostly > 130"C), showing how complexation influenced strongly the... 

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