Liquid crystalline phases smectic

The most significant differences (i.e. independence) in the analytical methods are provided in the final chromatographic separation and detection step using GC/ MS and LC-FL. GC and reversed-phase LG provide significantly different separation mechanisms for PAHs and thus provide the independence required in the separation. The use of mass spectrometry (MS) for the GC detection and fluorescence spectroscopy for the LG detection provide further independence in the methods, e.g. MS can not differentiate among PAH isomers whereas fluorescence spectroscopy often can. For the GC/MS analyses the 5% phenyl methylpolysiloxane phase has been a commonly used phase for the separation of PAHs however, several important PAH isomers are not completely resolved on this phase, i.e. chrysene and triphenylene, benzo[b]fluoranthene and benzofjjfluoranthene, and diben-z[o,h]anthracene and dibenz[a,c]anthracene. To achieve separation of these isomers, GC/MS analyses were also performed using two other phases with different selectivity, a 50% phenyl methylpolysiloxane phase and a smectic liquid crystalline phase. 

Fig. 6 Molecular structure of compound 6 and a change of its observed photoluminescent color on the nematic-smectic liquid-crystalline phase transition...

PHBA goes through an orthorhombic-to-hexagonal phase transformation (a rotational crystalline phase or a smectic liquid-crystalline phase). Other structures [720-/22] were recently described as belonging to the rotational crystalline state. 

Evans et al. also showed that the 1 1 mixture of BAN and (3, y-distearoyl-phos-photidylcholine (DSPC) gives a smectic A texture in the temperature range of 57.3 to 100°C [21]. This is the first notice of lyotropic lamellar liquid crystals formed in the ionic medium. Additionally, Seddon et al. [28] and Neve et al. [29] have described the long-chained A-alkylpyridinium or l-methyl-3-alkylimidazolium ions to display smectic liquid-crystalline phases above their melting points, when Cl or tetrachloro-metal anions like CoCl " and CuCl " are used as the counter ions. Lin et al. have also noted the liquid crystal behavior of 1-alkylimidazolium salts and the effect on the stereoselectivity of Diels-Alder reactions [30]. However, liquid crystals are classified as ionic liquid crystals (ILCs), and they are distinguished from liquid crystals that are dispersed in ionic liquids. Although the formation of micelles and liquid crystal phases in ionic liquids have been thus reported, there has been no mention of the self-assembly of developed nano-assemblies that are stably dispersed in ionic liquids. In the next section the formation of bilayer membranes and vesicles in ionic liquids is discussed. 

Problem 10.4 How does a smectic liquid-crystalline phase differ from a nematic ... 

Figure 1. Idealized representation of the molecular order in (a) nematic and (b) smectic liquid crystalline phases.

We have discussed the influence of the flexibility of the polymer backbone on the mesophase formation by examples of polyacrylates and polymethacrylates. More flexible polymers should have a stronger tendency to form more stable mesophases. Nevertheless, smectic liquid crystalline phases are the most common mesophases formed, if they do indeed form, by polymers in which no flexible spacers are used to connect main chain and... 

An initial approach to supramolecular H-bonded mesogenic polymer complexes involves a polyacrylate with 4-oxybenzoic acid moieties via a hexamethylene spacer 29 [26]. The 1 1 complexation of the side chain of the polymer and stilbazole 3 n - 2) (nematic, 168-216 °C) results in the formation of an extended supramolecular mesogen in the side chain (Fig. 11). Side-chain polymer complex 30 exhibits a nematic phase up to 252 °C, which shows that a significantly stabilized mesophase is achieved by the complexation of two different components. Liquid-crystalline properties have been examined for the series of complexes formed between polyacrylates and trans-4-alkoxy-4 -stilbazoles [33, 78]. Figure 12 shows transition temperatures against the carbon number of the alkyl chain for the series of complexes 31 [33]. They exhibit thermally stable smectic liquid-crystalline phases. For example, smectic E, B, and A phases are observed until 192 °C after the glass transition at 38 °C for the complex with m = 6 [78a]. 

It often happens that a substance possessing a smectic liquid crystalline phase just above the melting point passes into a nematic liquid crystalline phase at a higher temperature. Account for this type of behavior. 

The smectic liquid crystalline phase can be said to be more highly ordered than the nematic phase. In what sense is this true ... 

PBLG prepared via bacterial methods can form smectic liquid crystalline phases, while ordinary polydisperse PBLG exhibits nematic columnar, and cholesteric order in films and in solution. 

Figure 5.12 Small-angle X-ray scattering of association chain liquid crystalline polymer on cooling, q = 2 nld. The appearance of small-angle scattering indicates polymer exhibits a smectic liquid crystalline phase.

Fig. 1, X-ray diffraction from oriented smectic liquid crystalline phase...

Dantlgraber, G. Eremin, A. Diele, S. Hauser, A. Kresse, H. Pelzl, G. Tschierske, C. Chirality and macroscopic polar order in a ferroelectric smectic liquid-crystalline phase formed by achiral polyphilic bent-core molecules. Angew. Chem. Int. Ed. 2002, 41, 2408-2412. 

Several experiments performed with l,4-didodecyl-2,5-dipropynylbenzene at 150 °C with trifluoroeresol as cocatalyst furnished didodecyl-PPE 13b in excellent isolated yields (95-98%) with very high molecular weights (P 200-640, GPC vs. polystyrene) and polydispersities ranging from 3-7. All samples of 13b display melting points around 130-160°C and feature homeotropically aligned smectic liquid crystalline phases. ... 

In the smectic liquid crystalline phases the molecules exhibit additional... 

Molecular dynamics studies in chiral smectic liquid-crystalline phases by solid-state NMR measurements have been reported. The temperature dependence of the spin-lattice relaxation time Ti was investigated. For the aliphatic carbons in a flexible chain the value of Ti was found to increase with increasing temperature, because the molecular motion characterised by Xc was faster than the Larmor frequency coq-... 

The photoinitiated polymerization of a sterically hindered semi-fluorinated monomer, which is characterized by a hindered radical chain propagation site, was followed both in an isotropic and a highly ordered smectic liquid crystalline phase. The polymerization rate is slower in the smectic phase than in the isotropic phase, presumably a result of a decrease in both the propagation and termination rate constants. The decrease in the propagation rate results in a very slow persistent increase in polymer molecular weight after the initiating light source is removed. Polymerization firom the smectic phase of the monomer proceeds in a non-equilibrium matrix. 

There are a number of noteworthy examples of thermal bimolecular reactions which exploit the ability of liquid crystals to control solute orientations. One of the earliest and most studied examples is the quatern-ization reaction of alkyl p-dimethylamino-benzenesulphonate esters (7) in cholesteric and smectic liquid crystalline phases [357, 359, 363, 422, 423, 425]. 

There were two reports of the same bis(al-koxylsalicylidene) ethylenediamine complexes of Ni(II) and Cu(II), 52. The material was reported as giving a SmA phase at elevated temperature [122] and a noniden-tified mesophase [123]. Ohta later [124] found that the nickel complexes showed two smectic liquid crystalline phases, SmE and SmA. The SmE-SmA phase transition in the nickel complex is accompanied by a reversible stretching of the interlayer distances. This phenomenon can be ascribed to a dimer SmE-monomer SmA phase transition. 

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