• 한국염색가공학회지
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• 제3권1호
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• pp.28-36
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• 1991

Thermotropic behavior was observed in a number of aromatic copoly (ester amide)s containing a flexible spacer based on 4,4'$-dicarboxyalpha,\varpi-diphenoxy$ alkanes as an A component, di-acetylated p-aminophenol as a B, di-acetylated hydroquinone as a C gave the thermotropic copoly (ester amide)s containing a flexible spacer in the polymer backbone. 4,4'-diamino-3,3'-dimethoxybiphenyl as an amino group containing monomer as a D components. In the last case, up to 60 mol% of amide group was allowed to afford thermotropic liquid-crystallinity. The polymer structure and thermotropic nature were examined by solid-state and solution $^{13}C$ NMR spectroscopy, differential scanning calorimeter, polarizing microscopy, and IR spectroscopy.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.736-742
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• 2000

Mass removed from crystalline silicon samples during high power single-pulse laser ablation was studied by measuring the resulting crater morphology with a white light interferometric microscope. The volume and depth of the craters show a strong nonlinear change as the laser irradiance increases across a threshold value, that is, approximately $2.2{\times}10^{10}\;W/cm^2$. Time-resolved shadowgraph images of the ablation plume show the ejection of large particulates from the sample for laser irradiance above the threshold, with a time delay of about 300-400 nsec. The thickness of superheated liquid layer near the critical temperature was numerically estimated, considering the transformation of liquid metal into liquid dielectric near the critical state (i.e., induced transparency). The estimated thickness of the superheated layer at a delay time of 200 nsec agreed with the measured crater depths, suggesting that induced transparency promotes the formation of a deep superheated liquid layer which leads to an explosive boiling responsible for the sudden increase of crater volume and depth.

• Journal of information and communication convergence engineering
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• 제1권3호
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• pp.133-138
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• 2003

The preparation of $Al_{2}O_{3}-SiO_{2}$ thin films from less than one micron to several tens of microns in thickness had been prepared from metal alkoxide sols. Two methods, dip-withdrawal and electrophoretic deposition, were employed for thin films and sheets formation. The requirements to be satisfied by the solution for preparing uniform and strong films and by the factors affecting thickness and other properties of the films were examined. For the preparation of thin, continuous $Al_{2}O_{3}-SiO_{2}$ films, therefore, metal-organic-derived precursor solutions contained Si and Al in a chemically polymerized form has been developed and produced in a clear liquid state. In the process of applying to substrates, this liquid left a transparent, continuous film that could be converted to crystalline $Al_{2}O_{3}-SiO_{2}$ upon heating to $1000^{\circ}C$. And, a significant change of the film density took place in the crystallization process, thus leading to the strict requirements as to the film thickness, which could survive crystallization.

• Bulletin of the Korean Chemical Society
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• 제35권6호
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• pp.1613-1618
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• 2014

Perovskite-type oxides are promising oxygen carriers in producing oxygen-enriched $CO_2$ gas stream for oxyfuel combustion. In this study, a new series of $SrCo_{1-x}Fe_xO_{3-{\delta}}$ (x = 0.2, 0.4, 0.6, 0.8) was prepared and used to produce $O_2/CO_2$ mixture gas. The phase, crystal structure, and morphological properties of $SrCo_{1-x}Fe_xO_{3-{\delta}}$ were investigated through X-ray diffraction, specific surface area measurements, and environmental scanning electron microscopy. The oxygen desorption performance of $SrCo_{1-x}Fe_xO_{3-{\delta}}$ was studied in a fixed-bed reactor system. Results showed that the different x values of $SrCo_{1-x}Fe_xO_{3-{\delta}}$ have no obvious effects on crystalline structure. However, the oxygen desorption performance of $SrCo_{1-x}Fe_xO_{3-{\delta}}$ is improved by Co doping. Moreover, $SrCo_{0.8}Fe_{0.2}O_{3-{\delta}}$ synthesized via a new EDTA method has a larger BET surface area ($40.396m^2/g$), smaller particle size (48.3 nm), and better oxygen production performance compared with that synthesized through a liquid citrate method.

• Archives of Pharmacal Research
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• 제11권3호
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• pp.181-184
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• 1988

The effect of clover saponin on the phase transition of liposomal lipid bilayers of dimyristoyl phosphatidylcholine was investigated with differential scanning calorimetry. The thermograms of the liposomal bilayers incorporated with the clover saponin were obtained, and the enthalpy changes and the sizes of cooperative unit of the transition were calculated. The results showed that incorporation of the clover saponin into the liposomal bilayers effectively reduced the transition temperature at which the transition from solid state to liquid-crystalline state occurs, and broadened the thermogram peaks. It also reduced the size of cooperative unit of the transition. These results indicate that the clover saponin might have significant effect on the fluidity of biological membranes.

• 한국식품영양과학회지
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• 제27권3호
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• pp.518-524
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• 1998

Liposomes have been widely employed as biomembrane-mimetic system and drug-delivery system. In these applications, the low stability of liposomes has been the most serious problem. They have relatively short half-lives and easily lysed through interactions with biological components. This study was performed to investigate the effects of godulbaegi extracts on the fludity of phospholipid liposomes. We used dipalmitoyl phosphatidylcholine(DPPC) liposomes which make most stable liposomes among the other phosphatidylcholines. The thermograms of the DPPC liposomal bilayers incorporated with the hexane extract of godulbaegi(Ixeris sonchifolia H.) were obtained, and the enthalpy changes and the sizes of cooperative unit of the transition were calculated. The incorporation of the Ixeris sonchifolia H. into the liposomal bilayers effectively reduced the transition temperature at which the transition from gel state to liquid-crystalline state occurs, broadened the thermogram peaks, and reduced the ratio of van't Hoff to calorimetric enthalpies. These results indicate indicate that the godulbaegi extracts (Ixeris sonchifolia H.) have significant effects on the fluidity of biological membrance.

• 한국산학기술학회논문지
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• 제18권10호
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• pp.69-74
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• 2017

본 연구에서는, 화합물의 액정 형성을 위한 메소젠기로써 콜레스테릴기를, 고체에서 액정상으로의 열 전이온도를 조절하기 위한 구조로써 알킬기를 포함하고 있는 콜레스테릭 액정 화합물인 콜레스테릴 4-n-알콕시벤조에이트 (Chol-n)를 합성하고, 이들 분자 내에 있는 알킬기의 탄소 사슬의 길이가 액정 화합물의 물성에 미치는 영향을 조사하였다. 합성된 액정화합물의 화학 구조와 열적 성질 및 액정성은 적외선 분광분석 (FT-IR), $^1H$-핵자기공명 분광분석 ($^1H$-NMR), 시차주사열량분석 (DSC) 그리고 편광현미경 (POM)을 이용하여 조사되었다. 연구 결과에 의하면, 합성된 화합물들의 용융 전이온도 ($T_m$)는 $103{\sim}143^{\circ}C$였고, 화합물 Chol-6을 제외한 모든 화합물들은 약 $60{\sim}100^{\circ}C$의 넓은 액정상 온도 구간을 나타냈으며, 분자내의 탄소 원자 수와 화합물의 열적 성질 사이의 상관성은 발견할 수 없었다. 합성된 모든 화합물들은 양방성 콜레스테릭 액정상을 보였고, 화합물 Chol-6, 8, 9, 및 10은 카이랄 스멕틱 액정상을 동반하였다. 그리고, 모든 화합물들은 액정 상태에서, 온도가 높아질수록 붉은 색 계통에서 푸른 색 계통으로 색이 변하는, 열 변색 현상을 나타내었다.

• 공업화학
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• 제32권5호
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• pp.541-546
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• 2021

세라마이드와 인지질, 콜레스테롤 등과의 상호적 자가회합이 가능한 최적의 조성을 구성하여 세라마이드 고함량의 수화 액정형 베시클을 제조하였다. 혼합조성을 달리하여 다양한 베시클을 제조한 결과, 에지 액티베이터인 sodium deoxycholate (SDOC)와 가용화제인 PEG-60 hydrogenated castor oil (HCO 60)을 혼합하여 베시클을 만들었을 때, 가장 작은 나노 사이즈의 입자가 만들어지고, 베시클 분산액은 약산성이면서 가장 안정한 상태를 유지하였다. 또한 편광현미경과 열분석을 통해 SDOC와 HCO 60의 첨가가 세라마이드 등 지질 성분의 결정성 억제에 영향을 미치는 것으로 확인되었다. 베시클 분산액은 8주 동안의 고온의 장기 보관에서도 외관 및 점도의 변화없이 안정성이 그대로 유지되었다.

• Journal of Pharmaceutical Investigation
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• 제34권6호
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• pp.443-452
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• 2004

Habit is the description of the outer appearance of a crystal. If the environment of a growing crystal affects its external shape without changing its internal structure, a different habit results. Crystal habit and the internal structure of a drug can affect bulk and physicochemical properties, which range from flowability to chemical stability. A polymorph is a solid crystalline phase of a given compound resulting from the possibility of at least two different arrangements of the molecules of that compound in the solid state. Chemical stability and solubility changes due to polymorphism can have an impact on a drug's bioavailability and its development program. During crystallization from a solution, crystals separating may consist of a pure component or be a molecular compound. Solvates are molecular complexes that have incorporated the crystallizing solvent molecule in their lattice. When the solvent incorporated in the solvate is water, it is called a hydrate. To distinguish solvates from polymorphs, which are not molecular compounds, the term pseudopolymorph is used. Identification of possible hydrate compounds is important since their aqueous solubilities can be significantly less than their anhydrous forms. Conversion of an anhydrous compound to a hydrate within the dosage form may reduce the dissolution rate and extent of drug absorption. An amorphous solid may be treated as a supercooled liquid in which the arrangement of molecules is random. Amorphous solids lack the three-dimensional long-range order found in crystalline solids. Since amorphous forms are usually of higher thermodynamic energy than corresponding crystalline forms, solubilities as well as dissolution rates are generally greater. A study on crystal form includes characterization of (l)crystal habit, (2)polymorphism, (3)pseudopolymorphism, (4)amorphous solid.

• 대한전자공학회논문지
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• 제10권3호
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• pp.10-22
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• 1973

파정은 이것을 구성하고 있는 분자의 위치에 관하여서는 유동적이지만 분자축의 방향 변화에 대하여서는 탄성적인 것으로 그 탄성계수는 극히 적고 10-6dyne 정도다. 액정은 일반적으로 굴절율, 유전율, 자화율, 확산계수등에 있어 비교적 큰 비등방성을 가지는 것이 많다. 이와같은 액정이 지니는 성질을 잘 조합하면 다양한 응용의 가능성을 가진다. 전자공업의 표시장치, 또는 열효과를 이용한 비파괴 검사의 응용, 검지기 수용기의 응용, 시계, 광학기계, 분석기기에의 응용성 등이 주목되고 있다. 이 총설은 필자가 1972년 동경대학생산기술연구소에서 연구한 nematic 액정에 관한 전기화학적 및 광학적 연구를 최근의 액정에 관한 기초적 화학지식과 응용의 가능성에 대하여 소개한다.