• Elastomers and Composites
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• 제52권3호
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• pp.173-179
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• 2017

Side-chain liquid crystalline polymers having polysiloxane skeletons were synthesized by a thiol-ene reaction, using two kinds of mesogenic groups: a cholesteryl group for induction into a cholesteric liquid crystal phase and a triazomesogenic group for imparting light-sensitivity. All the synthesized polymers were crystalline, except the one with a single cholesteryl group. Crystallinity, glass transition temperature, and melt transition temperature increased with increasing content of the azomesogenic group. The polymer (P-C10A0) with a single cholesteryl group has a cholesteric phase, the one (P-C0A10) with a single azomesogenic group has a smectic phase, and those with both types of mesogenic groups showed both smectic and cholesteric phases. The temperature ranges of the two liquid crystalline phases in the co-polymers were independent of the contents of the two types of mesogenic groups. The rate of photoisomerization of the light-sensitive azobenzene group in the polymer decreased with increasing azobenzene content due to steric hindrance between the azomesogenic groups.

• Bulletin of the Korean Chemical Society
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• 제28권5호
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• pp.795-799
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• 2007

The bulk properties of poly(γ-benzyl-L-glutamate)-poly(ethylene glycol), PBLG-PEO, diblock copolymer were investigated. The helical transition from 7/2 to 13/5 for pure PBLG was at 120 oC while those of GE-1 and GE-2, which contain flexible PEO block 40 wt% and 60 wt% respectively, were shown at 135℃ on DSC experiments. FT-IR and XRD experiments were shown that the diblock copolymers maintained their α-helical structure in the temperature range between 25℃ and 175℃. Increasing relative size of coil part resulted in the increase of intermolecular packing distances. Due to well-maintained helical structure, lyotropic LC phases were observed for the PBLG-PEO block copolymer by the polarized optical microscope (POM). Especially, GE-3 copolymer, which has 12.5 wt% PEO contents, showed the smectic C phase. The competition of favorable aggregation energy between rod-rod and coil-coil, and unfavorable aggregation energy of rod-coil give rise to change the supramolecular structure in mixed solvent.

• 대한화학회지
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• 제42권6호
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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.

• Bulletin of the Korean Chemical Society
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• 제21권1호
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• pp.110-117
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• 2000

A series of new liquid crystalline dimesogenic compounds with chiral tails was synthesized, and their thermal and liquid crystalline properties were studied. The chain length of the central polymethylene spacers (x) was varied from dimethylene (2) to decamethylene (12). These compounds were characterized by elemental analysis, IR and NMR spectroscopy, differential scanning calorimetry (DSC), and cross-polarizing microscopy. All compounds were found to be enantiotropically liquid crystalline, and the values of melting ($T_m$) and isotropization temperature ($T_i$) as well as enthalpy change (Δ$H_i$) and entropy change for isotropization (Δ$S_i$) decreased in a zig-zag fashion revealing the so-called odd-even effect as x increases. Their mesomorphic properties fall into three categories depending upon x; (a) compounds with x=2 and 4 formed two different mesophases, smectic and cholesteric phases in that order on heating, and vice versa on cooling, (b) compounds with x=3, 7, 8, 10 and 11 reversibly formed only the cholesteric phase, and (c) compounds with x=5, 6, 9 and 12 exhibited only a cholesteric phase on heating, whereas on cooling they formed two different mesophases, cholesteric and smectic phases, sequentially.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2004년도 Asia Display / IMID 04
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• pp.1225-1228
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• 2004

We have studied the Polymer Stabilized Continuous Director Rotation (PSCDR) mode to solve the thermal shock problem which is core and main problem in CDR mode. The cell filled 95wt. % R2301 FLC and 5wt. % UCL-001 polymer is applied a low DC voltage only near the phase transition temperature from cholesteric to chiral smectic C phase transition to get defect-free alignment. In the previous work, we also confirmed layer deformation induced by an applied DC field only near the phase transition temperature from Ch to $SmC^{\ast}$. Results of layer structure, and characteristics of electro-optical properties between CDR and PSCDR mode will be discussed in this paper. We are also in progress to finalize the layer structures compared between CDR and PSCDR mode by x-ray measurements.

• 대한화학회지
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• 제40권5호
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• pp.365-373
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• 1996

Diethylenedisiloxyl 유연격자를 갖는 일련의 새로운 액정화합물을 합성하여 이들의 액정특성 및 말단의 페닐기에 para 치환기들의 스멕틱 그룹 효율성을 조사하였다. 또 말단그룹의 크기 영향을 알아보기 위하여 para 치환된 페닐 대신 $\beta$-naphthyl 그룹을 도입한 화합물도 아울러 합성하였다. 모든 화합물들은 85-95%의 높은 수율로 합성되었으며, 합성된 화합물들은 모두 양방성 액정 특성을 보여주었다. 이중 $X=NO_2$ 화합물은 $S_A$상을 보였고, 나머지 화합물들은 모두 $S_B$상을 보여주었다. 화합물들의 녹음열은 일반적인 액정화합물들과 비교하여 낮은 값을 나타내었으며 등방화열은 비슷한 값을 보였는데, 치환기의 스멕틱그룹 효율성은 $H 순이었다.

• Bulletin of the Korean Chemical Society
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• 제28권10호
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• pp.1651-1655
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• 2007

Rod-like polymerizable LC molecules having two different reactive groups, i.e. acryl and diacetylene groups were prepared. 4-Hydroxyphenyldiacetylenes were synthesized by the coupling reaction of 1-bromoalkynes with 4-ethynylphenol and then reacted with 4-(6-acryloyloxyalkyloxy)benzoic acid to give polymerizable LC molecules 4a-d. The mesomorphic properties of compounds 4a-d were investigated by differential scanning calorimetry, polarized optical microscopy and X-ray diffractometry. Compounds 4a-c exhibited smectic and nematic phases, but compound 4d having a longest alkyl tail among the series formed only a smectic phase. Photopolymerizability of acryl and diacetylene groups was investigated by IR spectroscopy. An anisotropic polymer film could be prepared by selective polymerization of acryl groups with 365 nm UV light in the presence of a photoinitiator (2,2-dimethoxy-2-phenylacetophenone). The subsequent reaction of diacetylene groups with 254 nm UV light disrupted the anisotropic structure, suggesting that these LC molecules could be used for imaging on the film.

• 한국응용과학기술학회지
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• 제13권3호
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• pp.51-60
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• 1996

A new one series of chiral schiff's base containing benzylidene aniline moieties was synthesized and characterized by IR, $^1H$ NMR. elementary analysis, and polarized optical microscopy(POM). The yield of these synthetic compounds was in the range of $62{\sim}67^{\circ}C$. The results showed that most of the synthetic compounds were monotropic liquid crystal and exhibited chiral smectic C($Sc^{\ast}$) liquid crystal phases, and the range of phase transition temperature was to $71.4^{\circ}C$ from $45.0^{\circ}C$.

• Near Infrared Analysis
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• 제1권2호
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• pp.21-27
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• 2000

Temperature-dependent changes in near-infrared (NIR) spectra have been measured for oleic acid, and nonanoic acid in the pure liquid state. Particular attention has been paid to the 5400-4800 cm$\^$-1/ region where a number of combination bands appear. The NIR spectra of oleic acid show that a band at 5303 cm$\^$-1/ increases with temperature while that at 5270 cm/sup-1/ decreases. It ha been found from their second derivative spectra that these spectral changes take place stepwisely with two break points at 30 and 53$\^{C}$, which correspond to the phase transition temperatures oleic acid reported previously. Principle component analysis (PCA) has been carried out for the NIR spectra of oleic acid in the 5400-4800 cm$\^$-1/ region measured over a temperature range of 15-80$\^{C}$. core plots of the first and second principal components (PCs) show that the NIR spectra are classified into three groups; the spectra measured in the temperature range of 15-30$\^{C}$, those in the range of 31-53$\^{C}$, and those in the range of 54-80$\^{C}$. These temperature ranges correspond to those for quasi-smectic liquid crystal, disordered liquid crystal, and isotropic liquid of oleic acid in the pure liquid state. In other words, PCA provides unambiguous evidence for the phase transitions. similar studies have been carried out for petroselinic acid and nonanoic acid in the pure liquid states, but they do not show any evidence for phase transitions.

• Bulletin of the Korean Chemical Society
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• 제27권9호
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• pp.1364-1370
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• 2006

New liquid-crystalline biphenyl carboxylates with an achiral swallow-tail derived from 1,3-dialkoxy-2-propanol $[(ROCH_2)_2CHOH$] where R is methyl, ethyl, propyl, butyl, $CH_2CF_3$, and $CH_2CF_2CF_3$ were prepared. These achiral liquid crystals having 1,3-dialkoxy-2-propyl moieties exhibit diverse phase sequences [I-SmA-(SmC)-(SmCalt)-Cr] depending on the substituent R group of the swallow-tail. The compounds carrying a fluorinated swallow-tail exhibit antiferroelectric-like smectic C phases, and their temperature ranges are broader than the corresponding non-fluorinated swallow-tailed ones.