Lyotropic nematic

FIGURE 2.3 51V NMR spectrum of vanadate in a nematic lyotropic liquid crystalline solution. The spectrum shows quadrupole-split signals from V and V4, while the signal of V2 is broadened. The quadrupole splittings are 200 Hz and 5.35 kHz for V and V4, respectively. The spectrum was obtained from a tetradecyltrimethylammonium bromide (TDTMABr) mesophase of composition TDTMABr, 160 mg decanol, 30 mg D20,450 mg NaCl, 10 mg. 

Pc macrocycle. Some of them are mesomorphic and show a Colh phase (Fig. 79 I-Gl G 115 Coin 270 I II-Gl G <-20 Colh > 320 h H-G2 G 115 Colh 250 I II-G3 94 Colh 108 I) for which the structure of the columnar mesophase is frozen at room temperature (anisotropic glasses). The functionalization of these dendrons in the 3 and 5 position of the terminal rings by oligo(ethyleneoxy) chains (0CH2CH2)30CH3, and their subsequent grafting onto the phthalocyanine of type I (Fig. 79) led to amphiphiUc materials [333]. In concentrated ethanol solutions ( 20-40% by mass), the compound with the fimctionaUzed G1 dendron behaves as a discotic amphiphUe forming a coliunnar nematic lyotropic phase. In addition, it possesses a columnar mesophase stable from room temperature up to 260 °C. Systems of type III are not mesomorphic. 

At high shear rates the chiral nematic structure changes to a flow-induced nematic phase. However, the shear-oriented phase is easy to disrupt after removing the shear force. This is because of the driving force for the liquid crystalline solution to form the more thermodynamically stable chiral nematic struc-ture. Relaxation in a pseudo-nematic lyotropic... 

Intermediate and deformed phases, including nematic lyotropic ... 

In both theories the aspect ratio of the rod (the shape anisotropy of the solute) determines the critical volume fraction of rods which, if exceeded, results in a spontaneously ordered phase of quasiparallel rods (a nematic lyotropic phase). 

Dialkoxy-PPEs are very similar to the dialkyl-PPEs, but considerably less stable. While dialkyl-PPEs can be melted without decomposition, dialkoxy-PPEs tend to degrade above 120°C and no thermotropic phases have been reported, however, nematic lyotropic preparations [58] were observed. The solid state ordering of dialkoxy-PPEs is similar to that of the dialkyl-PPEs [59]. Dialkoxy-PPEs are more electron rich and show a smaller bandgap than dialkyl-PPEs, i.e., their absorption and emission are redshifted with respect to that of the dialkyl-PPEs. Mixed systems have been reported by West, but seem to show properties that are more like those of dialkoxy-PPEs than those of the dialkyl-PPEs [10]. 

The cylindrical threads with a great ratio of the length to radius (/ r) form the so-called hexagonal (N) phase. Its sketch is similar to that for the columnar mesophase shown in Fig. 1.8(a). The opposite case is infinite flat lamellae which form the lamellar, smectic A-like (Fig. 1.2(b)) L-mesophase. In between, three nematic lyotropic mesophases are the Nq-... 

The concentration at which lyotropic phase is formed depends on the chemical stmcture and molecular mass of the polymer, the solvent nature, and the temperature. Generally, the effective concentration is in the range 10-20% by weight of the polymer in the solvent at room temperature. All polyamides form nematic lyotropic solutions, and the introdurtion of either a lateral substituent on the diamine, or of 1,3-phenylene units (in very small amoimts) or of flexible spacer (espedally polymethylene fragments) can increase the solubility of the polymers in the less a ressive solvent. 

Figure 28a displays a typical three-dimensional plot of the neutron intensity scattered by a nematic lyotropic solution in the (qv,qvv)-plane. The data were obtained on the SDS/Dec calamitic phase at 50 s (concentration c = 29.5 wt. % and R = [Dec]/[SDS] = 0.33). As shown in the iso-intensity contour plot (Fig. 28b), the patterns are characterized by two crescent-like peaks aside from the velocity axis. The maximum scattering corresponds to the first order of the structure factor, from which the distance between the center-of-mass of the micelles can be estimated (here 6 nm for a radius of nm). The modulation of the azimuthal intensity is also of interest since it reflects the distribution of micellar orientations. The spectra were analyzed in terms of angular distribution of the scattered intensity. The scattering was integrated over an elementary surface dgvdgvv = where corresponds typically to the half width at half... 

However, anisometry of the micellar aggregates is a necessary (yet not sufficient) prerequisite of liquid crystal formation. Indeed, at higher concentrations many perfluoro surfactants are known to form nematic, lyotropic, liquid, and crystalline phases [109]. One such system is the tetramethylammoniumperfluorononanoate (TMAPFN) which exhibits a nematic phase over a relatively large concentration range but only in a small temperature interval [91]. This system has been studied in detail by SANS [92]. The experiments showed that... 

Many cellulose derivatives form Hquid crystalline phases, both in solution (lyotropic mesophases) and in the melt (thermotropic mesophases). The first report (96) showed that aqueous solutions of 30% hydroxypropylceUulose [9004-64-2] (HPC) form lyotropic mesophases that display iridescent colors characteristic of the chiral nematic (cholesteric) state. The field has grown rapidly and has been reviewed from different perspectives (97—101). 

Lyotropic liquid crystalline nanoparticles have also been described. Concentrated solutions of gold nanorods in water in the presence of a surfactant (cetyltrimethyl-ammonium bromide) display a nematic mesophase stable up to 200 °C [74[. The N mesophase was identified by optical microscopy by their typical nematic droplets texture. 

Reinitzer discovered liquid crystallinity in 1888 the so-called fourth state of matter.4 Liquid crystalline molecules combine the properties of mobility of liquids and orientational order of crystals. This phenomenon results from the anisotropy in the molecules from which the liquid crystals are built. Different factors may govern this anisotropy, for example, the presence of polar and apolar parts in the molecule, the fact that it contains flexible and rigid parts, or often a combination of both. Liquid crystals may be thermotropic, being a state of matter in between the solid and the liquid phase, or they may be lyotropic, that is, ordering induced by the solvent. In the latter case the solvent usually solvates a certain part of the molecule while the other part of the molecule helps induce aggregation, leading to mesoscopic assemblies. The first thermotropic mesophase discovered was a chiral nematic or cholesteric phase (N )4 named after the fact that it was observed in a cholesterol derivative. In hindsight, one can conclude that this was not the simplest mesophase possible. In fact, this mesophase is chiral, since the molecules are ordered in... 

Discotic LC are formed by disk-like molecules with aromatic cores and side chains that are either hydrophobic (i.e., thermotropic) or hydrophilic (i.e., lyotropic). The discotic nematic (No) phase behaves like a normal nematic phase formed by rod-like molecules, and the disk-like molecules are oriented with their short molecular axes parallel to the director but show no positional order. More ordered columnar phases are commonly formed by thermotropic discotics. The two-dimensional structure can pack the columns into a hexagonal or rectangular columnar phase, while within the columns, disks can be... 

Lyotropic polymeric LC, formed by dissolving two aromatic polyamides in concentrated sulphuric acid, have been studied using variable-director 13C NMR experiments.324 The experimental line shapes at different angles w.r.t the external field were used to extract macromolecular order and dynamic in these ordered fluids. An interesting application of lyotropic LC is for the chiral discrimination of R- and S-enantiomers, and has recently been demonstrated by Courtieu and co-workers.325 The idea was to include a chiral compound 1-deutero-l-phenylethanol in a chiral cage (e.g., /1-cyclodextrin) which was dissolved and oriented by the nematic mean field in a cromolyn-water system. Proton-decoupled 2H NMR spectrum clearly showed the quad-rupolar splittings of the R- and S-enantiomers. The technique is applicable to water-soluble solutes. 

Quasi-nematic or compensated cholesteric phases were formed by CTC dissolved in mixtures of methylpropyl ketone (MPK) and DEME. CTC/MPK has a right-handed twist but CTC/DEME a left-handed one (109). Siekmeyer et al. (IIQ) studied the phase behavior of the ternary lyotropic system CTC/3-chlorophenylurethane/triethyleneglycol monoethyl ether. 

Note 3 In lyotropic systems, biaxial nematic mesophases have been identified from the biaxial symmetry of their tensorial properties. 

Note 5 If the mesogenic side-groups are rod-like (calamitic) in nature, the resulting polymer may, depending upon its detailed structure, exhibit any of the common types of calamitic mesophases nematic, chiral nematic or smectic. Side-on fixed SGPLC, however, are predominantly nematic or chiral nematic in character. Similarly, disc-shaped side-groups tend to promote discotic nematic or columnar mesophases while amphiphilic side-chains tend to promote amphiphilic or lyotropic mesophases. 

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