Gelation of delaminated layered double hydroxide nanosheets in formamide probed by proton spin-spin relaxation and pulsed field gradient NMR
Gelation of delaminated layered double hydroxide nanosheets in formamide probed by proton spin-spin relaxation and pulsed field gradient NMR
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DOI：
10.1021/jp072273n
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发表时间：
2007-08-16
影响因子：
3.7
通讯作者：
Wu, Qinglan
中科院分区：
文献类型：
--
作者：
Hansen, Eddy Walther;Norby, Poul;Wu, Qinglan
在甲酰胺中超声处理4-5 h，制备了层状双氢氧化物（LDH-NO3）剥离纳米片的胶体分散体。通过质子自旋-自旋弛豫和脉冲场梯度（PFG）核磁共振分析，发现了一个缓慢的凝胶化过程。在核磁共振时间尺度上，LDH颗粒被认为是一种被可移动的甲酰胺分子包围的不移动的基质，因此类似于多孔介质。当LDH颗粒在凝胶过程中重新排列并形成“网络”时，施加在甲酰胺分子上的空间约束（微米范围）随时间单调增加，导致甲酰胺在这种“多孔”介质中的扩散速度更快。通过结合质子核磁共振自旋-自旋弛豫速率测量（1/T-2）和pfg核磁共振测量（扩散），探测LDH粒子形成的空间限制的大小随时间的变化。本文讨论了分析中所采用的物理模型。
A colloid dispersion of exfoliated nanosheets of a layered double hydroxide (LDH-NO3) was prepared by ultrasonic treatment for 4-5 h in formamide. A slow gelation process takes place, which was followed using proton spin-spin relaxation and pulsed field gradient (PFG) NMR. On the NMR time scale, the LDH particles were considered as a nonmobile matrix surrounded by mobile formamide molecules, thus resembling a porous medium. The spatial constraints (micrometer range) imposed on the formamide molecules increase monotonically with time when the LDH particles rearrange and form a "network" during the gelation process, resulting in a faster diffusion of formamide within this "porous" medium. By combining proton NMR spin-spin relaxation rate measurements (1/T-2) and PFG-NMR measurements (diffusion), the size of the spatial restrictions formed by the LDH particles was probed as a function of time. The physical model applied in the analysis is discussed in the text.