Dependence of Pitch on Composition in Cholesteric Liquid Crystals

Adams, James E.; Haas, W.; Wysòcki, J. J.

doi:10.1103/physrevlett.22.92

Cited by 45 publications

(10 citation statements)

References 9 publications

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“…It is to be noted that a similar effect has been observed in mixtures of certain two-cholesteric liquid crystals. 8 However, at the present stage it is quite difficult to give a detailed discussion of this effect as no reliable theory exists yet.…”

mentioning

confidence: 94%

Helical Twisting Power in Mixtures of Nematic and Cholesteric Liquid Crystals

1971

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mentioning

confidence: 94%

Helical Twisting Power in Mixtures of Nematic and Cholesteric Liquid Crystals

1971

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“…reported for a similar dye-doped cholesteric system [19]. As can be seen from equation (1), the re ected wavewhere N 0 is the number of azo compound molecules per length can be aOE ected by a change of the helical pitch unit volume (before irradiation all of them are present or a change in the refractive indices of the mixture, both in the trans-form), U(x, y, t) is the radiation intensity, b of which can depend on the cis-isomer dopant concenis the quantum yield of photo-isomerization , K 0 is the tration.…”

Section: Resultsmentioning

confidence: 83%

“…It has the relative average amount of cis-isomers N(r 1 , r 2 ) 5 been reported previously that a dye-doped cholesteric 7 N cis 8 /N 0 in each concentric domain to be calculated. system exhibited a dP/dT > 0 with the dye in the pure N 0 , the amount of azo moieties per unit volume, can trans-form, but a negative dP/dT with the dye in the be estimated according to the formula N 0 5 CN A r/M, pure cis-form [19]. It would appear that in the material where C is the concentration of the azo moiety, N A is reported here, the cis-isomers also induce a negative Avogadro's number, r is the density (1 g cmÕ 1 ) and M variation of pitch with temperature, and, given the large is the molar mass (approximately 300 g molÕ 1 ).…”

Section: Theoretical Estimations and Discussionmentioning

confidence: 99%

Laser-induced concentric colour domains in a cholesteric liquid crystal mixture containing a nematic azobenzene dopant

Serak¹,

Arikainen²,

Gleeson³

et al. 2002

Liquid Crystals

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“…This is because the intensity of the scattered light increases over all the visible range, as is seen in the spectrum at 68.5 ~ in Figure 3. From these spectra, we may speculate that the scattered light is due to a selective reflection similar to that in a cholesteric liquid crystal [28][29][30] but not due to fluorescence. Note that the benzene solvent absorbs the light in the region of less than 280 nm wavelength, although the transparency spectrum has been measured in a double beam set-up with pure solvent as a reference.…”

Section: N 296mentioning

confidence: 94%

Thermochromism of polypropylene gels

Fujimatsu

Kuroiwa

1987

Colloid & Polymer Sci

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It is found that polypropylene gels in some solvents of benzene-derivatives show a striking change of colour. The colour changes from blue to yellow as the temperature rises from the melting point of the solvent to around 70-80 ~ The apparent characteristic of the phenomenon resembles the thermochromism of cholesteric liquid crystals although potypropylene itself is colourless and has no asymmetric carbons in the molecules. Polypropylene flakes swelled in these solvents also show similar thermochromism. [14][15][16][17][18][19][20]. However, all these investigations have been carried using dilute and quasi-concentrated solutions.We have previously reported on the gelation of the concentrated solutions of polyethylene in cyclohexane and carbondisulfide mixed solvent [21][22][23], successively, the gelation of the concentrated solutions of polyethylene [24][25][26] and polypropylene [27] also in a single organic solvent such as benzene, toluene, xylene, decalin, and tetralin. In preparing the gels, these solvents were added to polypropylene contained in glass tubes. The glass tubes were then sealed and the temperature raised up to near boiling point of the solvents. The polymer solutions were then cooled with running water until the gels were formed.When isotactic polypropylene flakes, prepared from xylene solution by addition of methanol, were swelled with benzene-derivative solvents prior to heating, the flakes were faintly coloured. A subsequent change of the temperature of these swelled polymer flakes resulted in the colour change. The yellowish colour at higher temperatures changed to a bluish colour at lower temperatures. N 296The gels prepared with these polymer flakes and the benzene-derivative solvents mentioned above also showed a faint colouring. On cooling the gels, the colour change was not as clear as that of the swelled polymer flakes. These gels were formed by gradual cooling of the polymer solution with running water. We therefore thought that the method of cooling might affect the thermochromic characteristics of the gels. In order to determine this, the polymer solutions were rapidly cooled to about-20 ~ Some of the solutions were frozen and others were not, but gels were formed anyway. Thus formed gels all showed clear thermochromism. Photographic plates (a) to (d) in Figure 1 show the thermochromism of the polypropylene gel in benzene.In order to make this more quantitative, the wavelength dependent transparency and the spectrum of light scattered in the direction perpendicular to the incident light were also measured. These are shown in Figures 2 and 3, respectively.The colour of the gels, as shown in the photographic plates in Figure 1, may be explained on the basis of the shape of the spectra in Figure 3. The spectrum of the light scattered from the gel at 26.5 ~ has a peak near 300 nm and a tailing edge in the wavelength range of 400 to 470 nm. Therefore, the scattered light itself appears to be bluish, resulting in the photographic plate, Figure la. As the temperature of the gel...

show abstract

Dependence of Pitch on Composition in Cholesteric Liquid Crystals

Cited by 45 publications

References 9 publications

Helical Twisting Power in Mixtures of Nematic and Cholesteric Liquid Crystals

Helical Twisting Power in Mixtures of Nematic and Cholesteric Liquid Crystals

Laser-induced concentric colour domains in a cholesteric liquid crystal mixture containing a nematic azobenzene dopant

Thermochromism of polypropylene gels

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