• Polymer(Korea)
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• v.30 no.1
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• pp.35-44
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• 2006

Poly[1-(cholesteryloxycarbonyloxy)ethylene](PCOE) and poly[1-(cholesteryloxycarbonylheptanoyloxy)ethylene] (PCOSE) were prepared by reacting poly(vinyl alcohol) with cholesteryl chloroformate or 8-cholesteryloxycarbonylheptanoly] chloride (CH8C), and their thermal and optical properties were investigated. CH8C formed a monotropic cholesteric phase whereas PCOE and PCOSE exihibited enantiotropic cholesteric phases. Like in the case of CH8C, the optical pitch $(\lambda_m)$ of PCOSE decreased with increasing temperature. PCOE, contrast with PCOSE, did not display reflection colors, suggesting that the helical twisting power or the cholesteryl group highly depends on the length or the spacer joining the cholesteryl group to the main chain. The mesophase properties of PCOE and PCOSE were entirely different from those of poly $(cholesteryl-\omega-acryloyloxyalkanoates)$. The results indicate that the mode of chemical linkage of the side chain group with the main chain plays an important role in the formation, stabilization, and temperature dependence of $\lambda_m$ of the cholesteric mesophase.

• Polymer(Korea)
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• v.28 no.1
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• pp.41-50
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• 2004

A new hydroxypropyl chitosan capable of forming a thermotropic liquid crystalline phase and two kinds of derivatives based on the hydroxypropyl chitosan (6-cholesteryloxycarbonylpentoxypropyl) chitosans (CHPCTs) and acrylic acid esters of CHPCT (CHPCTEs) were synthesized. The crosslinked films with liquid crystalline order were also prepared by photocrosslinking CHPCTE in mesophase. The liquid crystalline properties for all the samples and the swelling behavior of the crosslinked samples in acetone were investigated. In contrast with the hydroxypropyl chitosan, all the uncrosslinked cholesteryl-bearing samples farmed monotropic cholesteric phases with left-handed helicoidal structures and exhibited reflection colors over the full cholesteric range. This is the first report of a thermotropic cholesteric liquid crystalline chitosan derivative with reflection bands in the visible region. Both the optical pitches (λ$\_$m/'S) of CHPCT and CHPCTE decrease with temperature or with cholesteryl content at a given temperature. However, the λ$\_$m/ of CHPCT was larger than that of CHPCTE at the same temperature and at the same cholesteryl content. All the crosslinked samples did not display reflection colors, indicating that the cholesteric structure of CHPCTE significantly changes upon crosslinking. The two-dimentional anisotropic swelling characteristic of liquid crystalline networks was observed for all the crosslinked samples.

• Polymer(Korea)
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• v.36 no.3
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• pp.380-392
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• 2012

Four kinds of N,O-hydroxypropyl chitosans (HPCTOs) with degree of substitution(DS) and molar substitution (MS) ranging from 2.47 to 2.52 and 4.9 to 7.8, respectively were synthesized, and their molecular chracteristics and thermotropic and lyotropic liquid crystalline properties were investigated. MS was exceedingly larger than DS, showing that in the later stages of reaction, propylene oxide was preferentially added to the side chains rather than the main chain. All the derivatives formed thermotropic cholesteric phases. The glass and clearing temperatures were decreased with increasing MS. The optical pitches (${\lambda}_m$'s) of the thermotropic cholesteric phases increased with temperature. However, the ${\lambda}_m$'s of the derivatives at the same temperature increased with increasing MS. Solutions of HPCTOs in water, methanol, ethanol, acetic acid, and formic acid containing more than 30 wt% polymer also formed cholesteic phases whose ${\lambda}_m$'s decreased exponentially with increasing polymer concentration. The concentration dependence of ${\lambda}_m$ of HPCTO solutions, however, highly depended on the nature of the solvent and MS. The thermotropic and lyotropic mesophase properties of HPCTOs were significantly different from those reported for hydroxypropyl celluloses. The results indicate that the secondary amino group in the C-2 position plays an important role on the formation, stabilization, and temperature and concentration dependencies of ${\lambda}_m$ of the cholesteric mesophase.

• Polymer(Korea)
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• v.31 no.2
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• pp.148-152
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• 2007

The prototype of color fitters for the liquid crystal displays (LCD) using cholesteric liquid crystal monomers was produced. Cholesteric liquid crystal is characterized by the unique optical features of selective reflection, which is due to the helical twisting structures of LCs comparable to the wavelength of the incident light under certain conditions of substrate treatment. In the results of the experiment, cholesteric films for red, green, and blue light reflections respectively were produced and the viewing angle dependence of these films were investigated. Reflective light of red and green films shifted to shorter wavelength regions as viewing angle becomes greater, but blue one shifted very little. Periodic micrometer-sized half-spherical photoresist formed by thermal reflow method after photo-lithography was patterned on glass substrates. The viewing angle dependence of reflective light colors of red, green, and blue films on the patterned substrates compared with those on no patterned substrates was investigated. We could confirm the dependences were much smaller on the patterned substrates by bare eyes and Lab-color coordination methods qualitatively.

• Proceedings of the Optical Society of Korea Conference
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• 2007.07a
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• pp.129-130
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• 2007

• Polymer(Korea)
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• v.34 no.3
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• pp.242-246
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• 2010

FTIR spectroscopy has been employed in order to quantitatively investigate the relationship between planar arrangements and selective reflectance of cholesteric liquid crystals. It was found that the selective reflection was enhanced as the amount of planar arrangements in cholesteric liquid crystals increased. Although the planar arrangements of cholesteric liquid crystals can be induced only by the shear force effect, it was more effective to use the alignment layer to obtain the perfect planar arrangements.

• Korean Journal of Optics and Photonics
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• v.15 no.1
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• pp.63-67
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• 2004

We have obtained optical constants for cholesteric liquid crystal (CLC) films by fitting theoretical spectra of transmittance and reflectance with measured ones. Berreman's 4${\times}$4 matrix approach was used for the calculation of theoretical spectra. The fitting method was applied to three samples with different reflection bands and fitted results of refractive indices for CLC samples were compared with measured ones for a parallel-aligned LC sample. It was found that the two results were in fairly good agreement within the error of the fitted results for the three CLC samples.

• Polymer(Korea)
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• v.30 no.5
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• pp.422-425
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• 2006

Due to their periodic helical structure, cholesteric liquid crystals (CLC) have a unique ability to selectively reflect visible light. CLC films reflecting a broad wavelength band were prepared by inducing a pitch gradient in CLC layers through a diffusion of small molecules and through a thermal mixing of cyclic siloxane CLC molecules with different pitch lengths. Various pitch gradients in the CLC cell were observed using UV/Vis spectrometer and SEM technique.

• Polymer(Korea)
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• v.35 no.3
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• pp.272-276
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• 2011

The induction mechanisms of planar arrangements in cholesteric liquid crystals (CLC) which showed selective reflections of visible light were investigated by measuring the selective reflectivity and FTIR peak intensity of $C{\equiv}N$ stretching band. Although the planar arrangement of CLC was not as perfectly induced as the cases prepared with using alignment layers, it could be also induced by stretching polymer substrate or by applying shear forces. The planar arrangements were induced by forming CLC helical structures on top of liquid crystal molecules which were in contact with the substrate and oriented all in the same direction.

• Polymer(Korea)
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• v.31 no.1
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• pp.58-67
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• 2007

Fully cholesteryloxycarbonated and (8-cholesteryloxycarbonyl) heptanoated disaccharide derivatives were synthesized by reacting cellobiose, maltose, and lactose with cholesteryl chloroformate or 8- cholesteryloxycarbonylheptanoyl chloride, and their thermotropic liquid crystalline properties were investigated. All the cholesteryloxycarbonated derivatives (CH1DSs) formed enantiotropic cholesteric phases, whereas all the (8-cholesteryloxycarbonyl) heptanoated derivatives (CH8DSs) exhibited monotropic cholesteric phases with left-handed helicoidal structures whose optical pitches (${\lambda}m's$) decrease with increasing temperature. All the CH1DSs, contrast with the CH8DSs, did not display reflection colors over the full cholesteric range, suggesting that the helicoidal twisting power of the cholesteryl group highly depends on the length of the spacer joining the cholesteryl group to the disaccharide chain. The thermal stability and degree of order in the mesophase and the temperature dependence of the ${\lambda}m$ observed for EH8DSs were entirely different from those reported for the cholesterol-bearing dimers and triplet and the (8-cholesteryloxycarbonyl) heptanoated polysaccharide derivatives. The results were discussed in terms of the difference in the number of the mesogenic units per mole of repeating unit and the flexibility of the main chain.