• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.10
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• pp.69-74
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• 2017

In this study, cholesteryl 4-n-alkoxybenzoates (Chol-n), with alkyl groups used for controlling the temperature of transition to the liquid crystal phase, were synthesized, and the effects of the length of the alkyl groups on the physical properties of the liquid crystal compounds were investigated. The chemical structures and thermal and liquid crystalline properties of the synthesized compounds were investigated by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy ($^1H$-NMR), differential scanning calorimetry (DSC), and polarizing optical microscopy (POM). The synthesized compounds showed melting transition temperatures ($T_m$) in the range of $103^{\circ}C$ to $143^{\circ}C$ and all of the compounds except Chol-6 exhibited a wide liquid crystal phase temperature range of about $60^{\circ}C$ to $100^{\circ}C$. No correlation between the number of carbon atoms in the molecule and the thermal properties of the compounds was found. All of the synthesized compounds showed an enantiotropic cholesteric phase, which was accompanied by a chiral smectic phase in the compounds Chol-6, Chol-8, Chol-9, and Chol-10. All of the compounds exhibited thermochromism in the liquid crystal state, and their color changed from red to blue as the temperature was increased.

• Journal of the Korean Chemical Society
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• v.42 no.6
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• pp.679-695
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• 1998

A series of ${\alpha}{\omega}-bis[4-(4'-(S)-(+)-2-methylbutylbiphenyl-4-carboxy)phenoxy]alkanes$, were synthesized, and their thermal and liquid crystalline properties were studied. The chain length of the central polymethylene spacers, x, of the chiral twin compounds was varied from 3 to 12. These compounds were characterized by elemental analysis, IR and NMR spectroscopy, differential thermal analysis (DSC), and crosspolarized microscopy. All compounds were found to be enantiotropic liquid crystalline, and the values of melting $(T_m)$ and isotropization temperature $(T_i)$ as well as ${\delta}H_I$ and ${\delta}S_I$ decreased in a zig-zag fashion, revealing the so called odd-even effect as x increased. Their mesomorphic properties fell into four categories depending upon x; (a) compounds with x=3, 4 and 5 formed only a cholesteric phase on heating, while on cooling they went through two transitions of isotropic (I)-to-cholesteric (Ch) and Ch-to-smectic $A\;(S_A)$ phases before crystallization. (b) compounds with x=6, 8 and 10 exhibited only a cholesteric phase both on heating and on cooling. (c) compounds with x=7 and 9 went through three transitions of crystal $(C)-to-S_A,\;S_A-to-Ch,$ and Ch-to-I phases on heating while on cooling they went through four transitions of I-to-Ch, $Ch-to-S_A,\;S_A-to-Smectic\;C\;(S_C),\;and\;S_c-to-C$ phases in that order, and (d) compounds with x=11 and 12 went reversibly through four transitions of $C-to-S_C,\;S_C-to-S_A,\;S_A-to-Ch,$ and Ch-to-I phases.

• Korean Journal of Optics and Photonics
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• v.4 no.2
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• pp.168-172
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• 1993

We measured the spectral transmittance of the cholesteric mixtures of ZLI-1167 and CB15 for various weight fractions of CB15 in the mixture to find out the relationship between the center wavelength of the selective reflection band and the weight fraction of CB15 in the mixture. Left handed circular polarizer for 632.8 nm was designed and fabricated with this mixture whose weight fraction of CB15 was 33.19%. The ellipticity of the elliptical polarization of the transmitted light was measured to be 0.98 showing excellent property of the CLC circular polarizer.

• Korean Journal of Materials Research
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• v.3 no.3
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• pp.223-229
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• 1993

A homologous series of cholesteryl biphenyl ester derivatives was prepared. The thermal behaviors of compounds were studied by differential scanning calorimetry and by polarizing microscope equipped with a hot-stage. The cholesteric phase is present in all the compounds, whereas the smectic one is absent in the compounds with R = 1 and 2. The compounds possessed higher phase transitiof' temperature and wider temperature range of meso phase in comparison with known cholesteric liquid crystal phases.

• Elastomers and Composites
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• v.54 no.1
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• pp.14-21
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• 2019

Main-chain/side-chain liquid crystalline polymers (MCSCLCPs) combined with an azobenzene group and a cholesteryl group were synthesized to impart light and temperature sensitivity to the polymer. The polymers were designed with the azobenzene unit as the mesogenic group of the main-chain and various compositions of the azobenzene and cholesteryl units as the mesogenic group of the side-chain. The chemical structures and physical properties of the synthesized polymers were investigated by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, differential scanning calorimetry, thermogravimetric analysis, polarized optical microscopy, and ultraviolet-visible (UV-Vis) spectroscopy. All the MCSCLCPs were amorphous and exhibited enantiotropic liquid crystal phases; these polymers achieved the nematic phase with increasing content of the azobenzene group and exhibited the cholesteric phase with weak liquid crystallinity as the content of the cholesteryl group was increased. Furthermore, the polymers containing the azobenzene group showed photoisomerization when exposed to UV-Vis light, and the CP-A3C7 and CP-A5C5 polymers exhibited thermochromism in the temperature range of the liquid crystal phase.

• Proceedings of the Optical Society of Korea Conference
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• 2001.08a
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• pp.234-235
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• 2001

No Abstract.See Full-text

• Proceedings of the Korean Society of Potoscience Conference
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• 2005.06a
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• pp.136-136
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• 2005

• Proceedings of the Optical Society of Korea Conference
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• 2002.07a
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• pp.162-163
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• 2002

1-D photonic band-gap structure is identified in a cholesteric liquid crystal system. The optical transmission spectrum is measured and compared with the theoretical analysis. Nonlinear transmission is measured near the band edge. Also 3-D photonic band-gap structures are fabricated from dielectric colloidal polystyrene beads through a centrifuge method. The fabricated photonic crystals exhibit opalescent colors under white light and show a clear diffraction peak dependent on the incident angle of the light beam. Also the scanning electron microscope image was taken to verify the face-centered cubic crystal structure. Bragg's law and Snell's law are employed to describe the position of angle resolved diffraction peaks. It was shown that the optically deduced effective refractive index and lattice constants were in good agreement with the crystal structure identified by scanning electron microscope.

• Korean Journal of Crystallography
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• v.13 no.1
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• pp.21-24
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• 2002

The crystal structure of cholesteryl crotonate was investigated by X-ray diffraction. Crystallo-graphic data for the title compound: P2₁, a = 13.446(4) , b = 11.802(3) , c = 18.782(5) , β = 103.99(2)°, Z = 4. Reflections were collected with an Enraf-Nonius CAD-4 diffractometer equipped with a graphite monochromator. The structure was solved by direct methods and refined by least-squares analyses. The final R value was 0.092 for 1604 reflections. The cholesterol fragment of the title compound were in good agreement with those for related cholesterol derivatives. The molecules were stacked in clearly separated layers. At the center of the layers, there were cholesterol-cholesteryl interactions between the symmetry-related A molecules and the cholesteryl-C(17) side chain of B molecules. There were also interactions between the C(17) side chain of A molecules and the crotonate chains off and B molecules in the interface region between layers. The crystal structure of the title compound turned out to be isostructural with those of cholesteryl ethylcarbonate, cholesteryl propylcarbonate, and cholesterol crotylcarbonate. The crystals show the liquid crystalline state having the cholesteric phase.

• Journal of Biomedical Engineering Research
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• v.15 no.1
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• pp.89-96
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• 1994

The ether-type chitin derivatives were synthesized by reacting chitin with chloropropane, propylene oxide and chloropropane diol to form propyl chitin(PPC), hydroxypropyl chitin(HPC) and dihydroxypropyl chitin(DHPC). These derivatives formed a lyotropic cholesteric liquid crystallinity in concentrations over 30 wt% solution in formic acid (99%). Cast films from liquid crystalline solutions were degraded by lysozyme in pseudo-extra cellular tluid(PECF)solutions, at pH 1.2, pH 6.7 and pH 8.2. Three ether-type chitin derivatives rapidly degraded within the first week, and showed a decreased mechanical strength in neutral pH range. Dihydroxypropyl chitin showed the best biodegradation among these derivatives.