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Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals
Published on: May 29, 2018
Temperature-dependent structural changes in hydrogen bonds in microcrystalline cellulose studied by infrared and
Akihiko Watanabe1, Shigeaki Morita, Yukihiro Ozaki
1Department of Chemistry and Research Center for Near Infrared Spectroscopy, School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan.
Abstract:
Temperature-dependent structural changes in hydrogen bonds (H-bonds) in microcrystalline cellulose (MCC) were investigated by infrared (IR) and near-infrared (NIR) spectroscopy. The O-H stretching fundamentals and their first overtone bands were employed to explore the structural changes. In order to analyze the overlapping OH bands due to various H-bonds, perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy was applied to the IR and NIR data. Typical spectral variation temperatures were visualized by the PCMW2D correlation analysis. Structural changes in the strong H-bonds in MCC gradually occur in the temperature region of 25-130 degrees C, and they become greater above 130 degrees C. Both OH groups with H-bonds of intermediate strength and very weak H-bonds arise from the structural change of strong H-bonds in the temperature region of 40-90 degrees C, whereas the appearance of the latter OH groups with very weak H-bonds gradually becomes dominant above 90 degrees C. It is revealed from the present study that the glass transition at 184 degrees C induces the changes in the H-bonds in the Ibeta and the O3-H3...O5 intrachain H-bonds. Band assignments for the O-H stretching first overtone vibration region are proposed based on the results of the PCMW2D correlation analyses.
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