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( Oc Hee Han ),( Suk Bong Hong ) 한국공업화학회 2002 한국공업화학회 연구논문 초록집 Vol.2002 No.0
Even for the aluminosilicate zeolites with the same framework structure and composition, the location of catalytically active sites can differ according to the manner in which AI atoms are spatially distributed over the available tetrahedral sites in a given zeolite lattice. Thus, detailed knowledge concerning the local order of AI in these nanoporous materials is the starting point for systematically manipulating the distribution of acidic sites within their pore architecture.Results from the <sub>27</sub>AI MAS and MQMAS NMR measurements on a series of as-made ZSM-5 zeolites with 0.3 - 6.4 AI atoms per unit cell (Si/AI = 250 -14) provide the first direct evidence that the substitution of AI atoms over the 12 distinct tetrahedral sites (T-sites) in this particular structure type of zeolites during their crystallization process occurs in a non-random manner. Our detection methods are expected to be applied to other partially substituted samples also.
Characterization of Drawn Polyethylene by Solid State $^{13}C$ Magic Angle Spinning NMR
Han, Oc-Hee Korean Magnetic Resonance Society 1998 Journal of the Korean Magnetic Resonance Society Vol.2 No.1
Drawn polyethylene was studied by 13C cross polarization magic angle spinning techniques. Solid-solid phase transition from orthorhombic to monoclinic crystalline phase by drawing was observed. In addition, using a synchronized magic angle spinning 2 dimension technique, we confirmed that macroscopic ordering of the polyethylene was produced by drawing.
Possible Misinterpretation in Surface Adsorption Studies by CP-MAS NMR
Han, Oc-Hee,Bae, Yoon-Kyung Korean Magnetic Resonance Society 2008 Journal of the Korean Magnetic Resonance Society Vol.12 No.1
Cross-polarization (CP) signals were observed even from liquid samples such as neat toluene. Therefore, CP signals of liquid molecules in the presence of high surface materials do not necessarily mean the molecules are adsorbed on solid surface, especially when no signal from the tertiary observing nuclei such as carbons of the molecules is detected.
Solid State NMR Study of PAZO-6 and Related Materials
Han, Oc Hee,Jin, Jung-Il,Kim, Jong-Sung,Yoon, Yong-Kook,Huh, Sung-Mu 한국분석과학회 1995 분석과학 Vol.8 No.4
PAZO-6 is a new combined type liquid crystalline polymers (LCP) which has two types of mesogens combined non linearly. Ordering of branch mesogen azo group, in PAZO-6 is an important parameter to observe as well as the substitution effect on the backbone. The related small molecules sllch as monomers as well as the polymer itself are studied by solid state NMR techniques. Preliminary $^{13}C$ CP/MAS (cross polarization/ magic angle spinning) spectral results suggest that the azo groups in the monomers are not aligned with themselves. Azo groups in the monomers seem to be poorly ordered between well ordered p-phenylene terephthalate moeities. Similar disordering tendency of the azo group in PAZO-6 is deduced from the overall aromatic carbon peak positions which are not much different from those of the monomer.
Water Content Reduction in Poly(vinyl butylal) during Magic Angle Spinning
Han, Oc Hee,Jeong, SoonYong Korean Magnetic Resonance Society 2003 Journal of the Korean Magnetic Resonance Society Vol.7 No.2
Proton magic angle spinning spectra and thermogravimetric analysis data of poly(vinyl butylal) with water in it indicate water contents in the poly(vinyl butylal) samples were reduced during magic angle spinning. Our observation implies that the centrifugal force on the samples due to magic angle spinning cannot be neglected, especially on inhomogeneous and soft samples like poly(vinyl butylal) we tested in this work.
Han, Oc-Hee,Kim, Sun-Ha,Ko, Tae-Jung Korean Chemical Society 2009 Bulletin of the Korean Chemical Society Vol.30 No.5
To minimize the variance in the quantification of solid-state phases in powder samples, gently placing polycrystalline samples one next to another directly in a sample holder is better than trying to mix them homogeneously prior to transferring to a sample holder. However, the solid-state cross polarization-magic angle spinning (CP-MAS) nuclear magnetic resonance (NMR) spectroscopy results demonstrated that it is essential in this sampling method to place all the samples in the location of consistent signal sensitivity. The same sampling method may be employed in other spectroscopic quantification techniques of solid-state phases if the method to limit the sample to the location with uniform signal sensitivity in the sample holder is adapted to each technique.