• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.2
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• pp.188-194
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• 2000

Thermochromic liquid crystal reflect a unique color at even temperature. Therefore, they have been successfully applied to non-intrusive heat transfer research. Hue capturing method is widely used in the quantitative measurement from the TLC image. However it is affected by several measurement conditions. The distances of camera and light source have little influence on the color, but the value of hue is seriously affected by the measurement angle. In this study, the hue capturing method is improved by considering the effect of measurement angle. This improved calibration method can diminish the misreading of temperature caused by curvature of test surface.

• Polymer(Korea)
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• v.32 no.2
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• pp.169-177
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• 2008

The thermal and optical properties of cellulose tri(cholesteryloxy) carbonate(CCE0) and cellulose tri(cholesteryloxycarbonyl)alkanoates (CCEn, n=$2{\sim}8$, 10, the number of methylene units in the spacer) were investigated. CCE0 formed an enantiotropic cholesteric phase, whereas all the CCEn exhibited monotropic cholesteric phases. CCEn with n=$3{\sim}8$ formed cholesteric phases with left-handed helical structures whose optical pitches (${\lambda}_m's$) decrease with increasing temperature. On the other hand, CCE0 and CCEn with n=2 or 10 did not display reflection colors over the full cholesteric range, suggesting that the helical twisting power of the cholesteryl group highly depends on the length of the spacer connecting the cholesteryl group to the main chain. The thermal stability and degree of order in the mesophase and the temperature dependence of the ${\lambda}_m$ observed for CCEn highly depended on n. The results were discussed in terms of the differences in the internal plasticization, the arrangement of the side groups, and the conformation of the molecules.

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.2
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• pp.164-170
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• 2001

The influence of unsteady wake on the flow and heat transfer characteristics in a four-vane linear cascade was experimentally investigated. The unsteady wake was generated with four rotating rectangular plates located upstream of the cascade. Tested inlet Reynolds number based on chord length was set to 66,000 by controlling free-stream velocity. A hot-wire anemometer system was employed to measure turbulent velocity components. For the convective heat transfer coefficients measurement on turbine blade surface, thermochromic liquid crystal and gold film Intrex were used. It was found that the unsteady wake enhances the turbulent motion in the cascade passage and accordingly promotes the development and transition of boundary layer. It was found that the heat transfer coefficients on the blade surface increase as the plate rotating speed increases. However, the increasing of heat transfer coefficients is not significant in the case that Strouhal number is higher than 0.503.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.7
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• pp.864-870
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• 1999

An experimental study Is conducted in a four-vane linear cascade in order to examine the influence of the wake behind rectangular bars on the flow and heat transfer characteristics. Flow and heat transfer measurements are made for the inlet Reynolds number of 66000(based on chord length and free-stream velocity). Turbulent intensity and stress are measured using a hot-wire anemometer, and to measure the convective heat transfer coefficients on the blade surface liquid crystal/gold film Intrex technique is used. Each of experimental cases is characterized by the unsteadiness measured at the entrance of the cascade. The wake behind the rectangular bars enhances the turbulent motion of the flow in the cascade passage. It also promotes the boundary layer development and transition. The results show that heat transfer coefficients on the blade surface increase with increasing unsteadiness.

• 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.30 no.4
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• pp.338-349
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• 2006

Fully or nearly fully(8-cholesteryloxycarbonyl)heptanoated polysaccharide derivatives were synthesized by reacting cellulose, amylose, chitosan, chitin, alginic acid, pullulan or amylopectin with (8-cholesteryloxycarbonyl)heptanoyl chloride (CH8C), and their thermotropic liquid crystalline behaviors were investigated. Like in the case of CH8C, all the polysaccharide derivatives formed monotropic cholesteric phases with left-handed helicoidal structures whose optical pitches $({\lambda_m}'s)$ decrease with increasing temperature. Amylopectin derivative also formed a monotropic cholesteric phase with lefthanded helicoidal structures but, in contrast with the other derivatives, did not display reflection colors over the full cholesteric range, suggesting that the helicoidal twisting power of the cholesteryl group highly depends on the branched structure in amylopectin. The thermal stability and degree of order in the mesophase, the magnitude of ${\lambda}_m$ at the same temperature, and the temperature dependence of the ${\lambda}_m$ observed for polysaccharide derivatives were entirely different from those reported for the polymers in which the cholesteryl groups are attached to flexible or semiflexible backbones through flexible spacers. The results were discussed in terms of the difference in the chemical structures of the main and side chains and flexibility of the main chain.

• Polymer(Korea)
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• v.31 no.4
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• pp.356-367
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• 2007

Three kinds of amylose derivatives such as: cholesteryloxycarbonated amyloses(CAMs) with degree of esterification(DE) ranging from 1.8 to 3, (6-cholesteryloxycarbonyl)pentanoated amyloses(PAMs) with DE ranging from 0.3 to 3, and fully cholesteryloxycarbonated PAMs(CPAMs) were synthesized, and their thermotropic liquid crystalline properties were investigated. CAMs with $DE{\geq}2.6$, PAM with DE=1.6 and all the CPAMs formed enantiotropic cholesteric phases, whereas PAM with $DE{\geq}2.2$ exhibited monotropic cholesteric phases. PAM with $DE{\geq}2.2$ and CPAMs with (6-cholesteryloxycarbonyl)pentanoyl DE (DS) more than 1.0 formed cholesteric phases with left-handed helical structures whose optical pitches (${\lambda}_{m'}s$) decrease with increasing temperature. However, the ${\lambda}_{m'}s$ of these samples decreased with increasing DS at the same temperature. On the other hand, CAMs, PAM with DE=1.6, and CPAM with DS=0.3 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 main chain and DS. The thermal stability and degree of order in the mesophase observed for the amylose derivatives highly depended on DE or DS. The results were discussed in terms of the difference ul the hydrogen bond, the internal plasticization, and the decoupling of the motion of side group with the main chain.

• Polymer(Korea)
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• v.33 no.3
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• pp.254-262
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• 2009

Nine kinds of hydroxypropyl celluloses (HPCs) with degree of substitution (DS) and molar substitution (MS) ranging from 2.10 to 2.71 and 2.3 to 6.7, respectively and seven kinds of fully butanoated HPCs (BPCs) based on the HPCs with $2.3\;{\le}\;MS\;{\le}\;6.7$ were synthesized, and the molecular characteristics of HPCs and the thermotropic liquid crystalline properties of the derivatives were investigated. MS was nearly equal to DS for small value of DS, but it became exceedly larger than DS for $DS{\gtrsim}1$, showing that in the later stages of reaction, propylene oxide preferentially adds to the side chains rather than the main chain. All the derivatives formed enantiotropic cholesteric phases with right-handed helical structures. The glass and clearing transition temperatures of both HPCs and BPCs were decreased with increasing MS. The optical pitches (${\lambda}_m'S$) of BPCs, as well as HPCs themselves, increased with increasing temperature. However, the ${\lambda}_m'S$ of both HPCs and BPCs at the same temperature increased with increasing MS. Moreover, the temperature dependence of ${\lambda}_m$ of HPCs was weaker than that of BPCs, suggesting that the helical twisting power of the cellulose chain highly depends on the length and chemical structure of the side chain introduced in cellulose chain.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.351-351
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• 2010

OLED(organic light emitting diode)는 액정디스플레이를 대체할 차세대 평판디스플레이로 많은 주목을 받고 있다. 현재 많이 사용되고 있는 OLED의 기판재료는 Glass기판이지만 차세대 Flexible한 display에서의 적용을 위해서는 가볍고 유연한 plastic을 기판 재료로 사용 할 것으로 보인다. 하지만 plastic이 기판재료로 된 OLED의 가장 큰 단점중의 하나가 수분과 산소에 민감하여 열화를 초래한다는 것이다. 이런 수분침투와 열화 과정으로 인해 OLED의 발광효과가 약해져 OLED의 수명과 직접적으로 연결된다. 하여 외부에서 OLED내부로 유입되는 산소, 수분으로 부터 발광재료와 전극의 산화를 방지하며 외부의 충격으로부터 소자를 보호하기 위한 봉지기술은 반드시 필요하다. 따라서 본 연구에서는, flexible한 OLED에 적용되는 금속 코팅한 막의 적층구조 및 기판의 노출온도에 따른 금속 코팅막의 수분침투 특성에 대해 MOCON의 weight gain test (WGT)를 통해 barrier layer에 대해 평가하고 이에 대한 mechanism을 확립하는데 그 목적이 있다. 금속을 코팅한 막은 OLED의 cathode와 anode 재료로 많이 사용되는 Al과 ITO를 sputter장비를 이용해 single layer와 double-layer의 두 가지 구조로 PET기판에 증착하였다. 증착한 Al막의 두께는 각각 50 nm, 100 nm, 200 nm, 400 nm 등 4가지로 하였다. double-layer의 경우에는 총 두께를 절반씩 기판의 양쪽에 증착하였다. 적층구조에 따른 수분침투 특성 평가 결과로 보면 같은 두께일 때 double-layer는 single layer에 비해서 모든 시편에서 수분의 투습율이 낮음으로써 더 좋은 수분침투의 barrier 특성을 나타내었다. 특히 100 nm이상인 경우 투습율은 예상한 값보다 50%이상 낮게 나타났다.