水溶液
红外光谱学
溶解度
红外线的
材料科学
化学
分析化学(期刊)
化学工程
有机化学
光学
物理
工程类
作者
Hiroyuki Kakuda,Tetsuo Okada,Takeshi Hasegawa
摘要
The chain conformation and hydration structure of an aqueous solution of linear poly(ethylene imine) (LPEI) have been studied by the use of mid-infrared (mid-IR) and near-infrared (NIR) spectrometries to explore the molecular mechanism of an upper critical solution temperature (UCST)-type solubility change. When LPEI was dissolved in water, the solution became a gel at room temperature. Mid-IR and NIR absorption bands of the LPEI gel appeared at the same positions as the bands of the dihydrate crystal of LPEI in a film, which suggested that LPEI formed dihydrate crystallite in water at room temperature. This means that LPEI is in a planar-zigzag structure even in water at room temperature. When the gel was heated, it was changed to a transparent aqueous solution. Both mid-IR and NIR bands of an LPEI aqueous solution above 64 °C exhibited a broader bandwidth than those at room temperature. Judging from the change of the bandwidth, the LPEI chain in water was disordered by heating to take a random-coil form. In addition, band locations of the CH stretching first-overtone vibration bands in a NIR spectrum of the solution above 64 °C were higher than those of melted dry LPEI, which was reasonably understandable that the disordered LPEI chains in the aqueous solution were in a highly hydrated state. These spectral results have revealed that the change from the planar-zigzag form to the random-coil one in water is a trigger to begin the UCST-like solubility change on heating followed by hydration.
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