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Study of Sol-gel Transition using Various NMR Techniques

使用各种 NMR 技术研究溶胶-凝胶转变

基本信息

批准号：
01550684
负责人：
HIKICHI Kunio
金额：
$ 1.09万
依托单位：
Hokkaido University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1990
项目状态：
已结题

项目摘要

Kappa -Carrageenan gel which is formed by the addition of Rb^+ ion to its aqueous solution undergoes a transition into sol in the vicinity of 55^ﾟC with increasing temperature. In order to examine the behavior of water molecules in the gel, we measured the self-diffusion constant of water molecules by the nuclear magnetic resonance method.The kappa -carrageenan gel was prepared by adding 50mM RbCl to 5wt% kappa -carrageenan aqueous solution. The self-diffusion constant was measured by the combined use of the Carr-Purcell-Meiboom-Gill method and the field gradient method using JEOL JNM-FX60 equipped with a PL502 field gradient unit. The field gradient unit was calibrated using the known self-diffusion constant of pure water at room temperature.We measured the temperature dependence of the self-diffusion constant of pure water molecules in the temperature range from 25 to 75^ﾟC. The observed value was found to agree well with the value in the literature. We also measured the temperature dependence of the self-diffusion constant of water molecules of the 5wt% kappa -carrageenan aqueous solution. The values are almost the same as those of pure water.The temperature dependence of the self-diffusion constant of the kappa -carrageenan gel was measured. It was found that the self-diffusion constant of water molecules in the gel state is smaller than that of pure water, indicating the restricted translational motion of water molecules inside the gel network. In the vicinity of 55^ﾟC where the gel-to-sol transition occurs, the self diffusion constant abruptly increases and approaches the value of pure water. The results indicate that the transition releases the translational freedom of motion of water. When the temperature is lowered, the transition region shifts to lower temperature, showing the hysteresis. The data were found to scatter in the transition region, supposedly implying the critical relaxation.

Kappa-卡拉胶是通过在其水溶液中添加Rb^+离子而形成的，随着温度的升高，在55℃附近转变为溶胶。为了考察水分子在凝胶中的行为，我们采用核磁共振法测量了水分子的自扩散常数。在5wt%的κ-卡拉胶水溶液中加入50mM RbCl制备了κ-卡拉胶凝胶。通过组合使用Carr-Purcell-Meiboom-Gill方法和使用配备有PL502场梯度单元的JEOL JNM-FX60的场梯度法来测量自扩散常数。利用已知的纯水在室温下的自扩散常数来校准场梯度单元。我们测量了纯水分子在25至75^ﾟC温度范围内的自扩散常数的温度依赖性。发现观测值与文献中的值非常吻合。我们还测量了 5wt% kappa -卡拉胶水溶液的水分子自扩散常数的温度依赖性。该值与纯水的值几乎相同。测量了κ-卡拉胶凝胶的自扩散常数的温度依赖性。研究发现，凝胶态水分子的自扩散常数比纯水小，表明水分子在凝胶网络内部的平移运动受到限制。在发生凝胶到溶胶转变的55^ﾟC附近，自扩散常数突然增加并接近纯水的值。结果表明，转变释放了水的平移运动自由度。当温度降低时，过渡区向较低温度移动，表现出滞后现象。发现数据分散在过渡区域，这可能意味着临界松弛。