Mixture cholesteric

Induction of chirality in No phases was also shown to be possible using charge transfer interactions, via jt-jt stacking. The binary mixture of mesogen 8, which is electron rich, with chiral electron-deficient molecule 9 was shown to induce a twist in the mesophase.15 Furthermore, nonmesogenic 8 gave rise to a cholesteric mesophase, denoted as being of the columnar type (N ), when present in a ternary system with TNF (trinitrofluorenone, an electron acceptor)... 

AY Bobrovski, NI Boiko, VP Shibaev, and JH Wendorff, Cholesteric mixtures with photochemi-cally tunable, circularly polarized fluorescence, Adv. Mater., 15 282-287, 2003. 

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. 

Sensitized for blue-green or red light, photoconductive polyimides and liquid crystal mixtures of cyanobiphenyls and azoxybenzene have been used in spatial light modulators [255-261]. Modulation procedure was achieved by means of the electrically controlled birefringence, optical activity, cholesteric-nematic phase transition, dynamic scattering and light scattering in polymer-dispersed liquid crystals. 

For CD observation, pyrene-2-carboxylic acid methyl ester was dissolved into a cholesteric mixture of 55.5 mole percent of cholesteryl nonanoate and 44.5 mole percent of cholesteryl chloride, which exhibited a pitch band CD with plus sign... 

Fig. 29. Inverse wavelength of reflection LR 1 vs. concentration in mole % of the chiral component for induced cholesteric phases = copolymer No. 5, Table 8 O = monomer-polymer mixture...

In each mesophase mixture, the dominant atropisomer after photo or thermal resolution experiments was S(+). The sole exception occurred during irradation of a 3% BN solution in mixture C. Since the sample solidified partially during the experiment, the mechanism by which the R(-) atropisomer arose is unclear. The thermal lability of the atropisomers toward interconversion and the possible contribution of cholesteric contaminants in recovered BN samples make an accurate assessment of atropisomeric excess a formidable task. Extreme care was taken to handle all solutions containing BN during work-up at temperatures which preclude significant thermal racemization at 25°C, the half-life for racemization is ca. 10 h in normal isotropic solvents all manipulations were conducted at 4°C or below. 

Addition of a ca. 10% concentration of CA to a mesophase solution (mixture E) of BN quenches completely its photoresolution. CA quenches singlet states of BN in n-hexane at a nearly diffusion-controlled rate (kq = 101- -tf -s- assuming tbn = 3 ns (34-36)). Thus, even In a very viscous medium like cholesteric mixture E, static and dynamic quenching should preclude formation of BN triplets. 

Our spectroscopic studies of BN in mixture B and in hexane support our contention that ground state conformers are forced by cholesteric mesophases toward extremes of 0 (i.e., closer to 0° or 180° than in hexane solvent). As the two naphthyl groups become more coplanar, their u-overlap increases. Consequently, the 0-0 transitions in absorption (and excitation) occur at longer wavelengths (lower energies) (43). For the same reasons, the cholesteric solvent compresses excited singlets of BN, causing their fluorescence spectra to be red-shifted with respect to those in hexane. 

We arrive at this conclusion from the lack of more than a slight atropisomeric excess (ca. 0.1% in all but one anomalous experiment) after equilibration of racemic BN in the cholesteric phases at several temperatures (TablelV). The lack of change in the ratio of atropisomers in the cholesteric phases is consistent with our observation that liquid-crystal induced circular dichroism spectra (67) of ISN in cholesteric mixture D are due to a macroscopic property of the solvent the LCICD spectra disappear when mixture D is heated to an isotropic temperature. 

Figure 3. Plot of ln[ ([a]t-[a] )/[a]0-[a] >)] versus time for the thermal raceraization of S(+)-BN in cholesteric mixture C at 23.0°C. Data from three independent kinetic runs represented by 0, , and A are fitted to a single line.

That both phenomena arise as a consequence of macroscopic solvent order and not Intimate solvent-solute Interactions Is clear Saeva and 01In (75) have shown that solute LCICD spectra can be observed In twisted nematic phases only Nakazaki et al. (76) find an excess of one enantiomer of hexahelicene Is produced photochemlcally from achiral precursors In twisted nematic phases no LCICD spectra or optical Induction occurs In untwisted nematic phases and the handedness of the twist can be correlated with the sign of the LCICD and the preferred product enantiomer. Furthermore, Isotropic phases of cholesteric mixtures display no discernible LCICD spectra (12, 67) and the enantiomeric excesses In products of photolablle reactants In Isotropic phases are near zero (51). 

It was really only a matter of time until researchers in the field started doping blue phases with quasi-spherical nanoparticles. This area is very much in its infancy, but the few recent reports already show some promising results. Yoshida et al., for example, reported on an expansion of the temperature range of cholesteric blue phases from 0.5 to 5°C by doping blue phases with gold nanoparticles (average diameter of 3.7nm) as well as a decrease in the clearing point of approximately 13°C [427]. A similar effect was also observed by Kutnjak et al. for CdSe quantum dots simultaneously capped with oleyl amine and TOP (diameter of the core 3.5 nm) in CE8 (Merck) and CE6 (BDH). The authors found that particularly blue phase III was stabilized in these mixtures, blue phase II destabilized, and... 

For example, the selective reflection of a cholesteric mixture of derivative 1 ( 45 wt %)/monomer 2 (diethylene glycol dimethacrylate) covered the whole visible spectrum in a narrow temperature range i.e., the mixture was bluish at 20 °C, greenish at 30 °C, and reddish at 50 °C. Therefore, by successive photo-crosslinking of the liquid-crystalline sample at different temperatures through a mask, a colored picture or pattern could be fixed onto the resulting composite film. 

Fig. 14 UV-VIS spectra of a cholesteric elastomer, based on a mixture of derivative 2 (44 wt %), monomer 1 (52wt%), and monomer 2 (3wt%), crosslinked at 32 °C. Arrows indicate the maximum position of the selective light-reflection band. (Reproduced from [233])...

Lanolin and lanolin alcohols are excellent emulsifiers, giving oil-in-water emulsions, and can be combined with additional emulsifiers such as cetearyl alcohol to improve stability.8 The ability of anhydrous lanolin and especially lanolin alcohols to form stable emulsions with up to 300% (w/w) of water distinguishes lanolin from petrolatum in its physical properties.1 The chemical compositions of lanolin and petrolatum are also very different, as petrolatum is composed completely of hydrocarbons.16 Lanolin alcohols and petrolatum can be combined to form cholesterized petrolatum, which also has the capacity to form emulsions. For example, a mixture of 65% (w/w) lanolin, 20% (w/w) water, and 15% (w/w) petrolatum can incorporate an equivalent weight of water without changing its consistency.15,52... 

The valency of the hydrogen bond donors and acceptors can be varied to produce chiral mesophases [85]. Mixtures of the divalent 4,4 -bipyridine with 4-[(S)-2-methylbutoxy]benzoic acid in ratios between 1 9 and 4 6 show LC behaviour, but the chiral mesophases are exhibited for only a small range of compositions [86]. Here, the cholesteric and a blue LC phase were observed. The association of the acid to the bipyridine was confirmed by a crystal structure of the 1 2 complex. 

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