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Chung, Jae Woo,Son, Se-Bum,Chun, Sang-Wook,Kang, Tae Jin,Kwak, Seung-Yeop Wiley Subscription Services, Inc., A Wiley Company 2008 Journal of polymer science Part B, Polymer physics Vol.46 No.11
<P>Exfoliated poly(ethylene terephthalate) (PET)-layered silicate nanocomposites (P<SUB>et</SUB>LSNs) excluding (P<SUB>et</SUB>LSN<SUB>eom</SUB>) and including (P<SUB>et</SUB>LSN<SUB>iom</SUB>) organic modifiers were obtained by solution methods with and without solvent-nonsolvent system, respectively. From wide angle X-ray diffraction and high resolution transmission electron microscopy, both P<SUB>et</SUB>LSNs were found to have exfoliated structure attributed to sufficient dispersion of silicate in prepared solvents, regardless of sample preparation method. However, organic modifier in P<SUB>et</SUB>LSN<SUB>eom</SUB> was confirmed to be well removed by elemental analysis, whereas organic modifier was still remained in P<SUB>et</SUB>LSN<SUB>iom</SUB>. Thus, the effect of the presence and absence of organic modifiers in P<SUB>et</SUB>LSNs on the nonisothermal crystallization behavior was investigated by differential scanning calorimetry (DSC) on the basis of a modified Avrami analysis and polarized optical microscopy (POM). From DSC results, it was found that both P<SUB>et</SUB>LSNs had higher degrees of crystallinity and shorter crystallization half-times than neat PET, because of the dispersed silicate layers acted as nucleating agents in both P<SUB>et</SUB>LSNs. However, P<SUB>et</SUB>LSN<SUB>iom</SUB> exhibited a lower degree of crystallinity and longer half-time of crystallization than P<SUB>et</SUB>LSN<SUB>eom</SUB>. Difference of crystallization behavior between P<SUB>et</SUB>LSN<SUB>eom</SUB> and P<SUB>et</SUB>LSN<SUB>iom</SUB> was ascribed to organic modifier in P<SUB>et</SUB>LSN<SUB>iom</SUB>, which may act as crystallization inhibitors. POM measurements also revealed the results which were in good agreement with crystallization behavior observed from DSC measurement. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 989–999, 2008</P>
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이량체액정 ( CBA -10 ) 의 상전이에 따른 열역학적 특성에 관한 연구
강봉근,곽선엽,남수용 ( Bong Geun Kang,Son Yeop Kwak,Su Yong Nam ) 한국공업화학회 1997 공업화학 Vol.8 No.5
주쇄형고분자액정(CBA-10)의 PVT와 ²H-NMR측정으로 상전이에 따른 열역학적 특성을 고찰하였다. 부피 변화에 의한 Nl 및 CN 상전이가 발생하였으며, 일정체적하의 상전이 엔트로피 (△S_NI)_v와 (△S_CN)_v값 12.6, 65.3J/㏖·K를 각각 구하였으며, 체적변화에 따른 엔트로피는 일정압력하에 얻어진 전이엔트로피의 40∼60%정도였다. ²H-NMR/RIS 해석으로 nematic conformation을 결정하였으며, Nl 및 CN 상전이에 의한 conformation entropy를 구하여 PVT측정에서 구한 일정체적하의 엔트로피와 비교한 결과, 거의 대응하다는 것을 알 수 있었다. 이러한 결과로부터 주쇄형액정의 상전이에 있어서 spacer conformation 변화가 중요한 역할을 하고 있음을 밝혔다. The PVT and ²H-NMR characteristic of main-chain dimer liquid crystals having structures such as α,ω-bis[4,4`cyanobiphenyl) oxy] alkane(CBA-10) were studied In this work, V-T curves obtained from isobaris measurements on various pressures, volume changes were observed at the nematic-isotropic and nematic-crystal phase transition. The volume changes at the transition exhibit slight odd-even effect with respect to the number of methylene unit n. The values of the (△S_tr)_v obtained at the NI transition for CBA-10 was 12.6J/㏖·K The values of (△S_CN)_v for the CN transition was estimated on the basis of DSC data : 65.3J/㏖·K For both transition, it was found that the correction about the volume change is significant, ranging from 40 to 60% of the total transition entropy observed under constant pressure. The RIS analysis of the spectra was performed so as to elucidate the conformational characteristics of the spacer in the nematic phase. The conformational entropy changes at both CN and NI interphases were estimated on the basis of the nematic conformations taken from the conformation map as well as those derived from the simulation. The estimated conformational entropy change values were then compared with the corresponding constant-volume entropies obtained from PVT measurements. The correspondence between both entropy values was found to be quite good in consideration of the uncertainties involved in both experiment and calculations.
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