Dobies Maria, Kozak Maciej, Jurga Stefan
Department of Macromolecular Physics, Institute of Physics, Adam Mickiewicz University, Umultowska 85, Poznań 61-614, Poland.
Solid State Nucl Magn Reson. 2004 Jan;25(1-3):188-93. doi: 10.1016/j.ssnmr.2003.03.019.
The Fast Field Cycling Relaxometry and the dynamical rheology were applied to study the gelation process in aqueous low methoxyl pectin solution in the presence of divalent cations from the calcium chloride. The model-free approach to the analysis of 1H NMRD data was used to separate the information on the static and dynamic behaviour of the system provided by the dispersion profiles of the systems tested. Mechanical spectroscopy was applied as a complementary method to probe the network formation. The structural changes were most pronounced for the concentration of calcium chloride between 10 and 15 mM (the static parameter beta was found to vary from 0.936 x 10(7) to 1.27 x 10(7) 1/s2) revealing the sol-gel transition on visual inspection. The presence of the gel network was confirmed by the rheological measurements. All mechanical spectra exhibited the gel like character, and the solid like response was more evident at higher concentrations of calcium cations. The mean correlation time <tau(c)> increased with increasing salt concentration, but remained unchanged for the concentrations above 15 mM. The dynamical changes were most significant at the phase transition from the sol to the gel state.
采用快速场循环弛豫测量法和动态流变学方法，研究了在氯化钙提供的二价阳离子存在下，低甲氧基果胶水溶液中的凝胶化过程。采用无模型方法分析1H NMRD数据，以分离由测试系统的色散曲线提供的关于系统静态和动态行为的信息。应用机械光谱法作为探测网络形成的补充方法。当氯化钙浓度在10至15 mM之间时，结构变化最为明显（静态参数β从0.936×10⁷变化至1.27×10⁷ 1/s²），通过目视检查可观察到溶胶-凝胶转变。流变学测量证实了凝胶网络的存在。所有机械光谱均呈现出凝胶状特征，并且在较高浓度的钙阳离子下，固体状响应更为明显。平均相关时间<τ(c)>随盐浓度的增加而增加，但在浓度高于15 mM时保持不变。在从溶胶到凝胶状态的相变过程中，动态变化最为显著。
