Gelation of Delaminated Layered Double Hydroxide Nanosheets in Formamide Probed by Proton Spin−Spin Relaxation and Pulsed Field Gradient NMR

A colloid dispersion of exfoliated nanosheets of a layered double hydroxide (LDH-NO 3 ) 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.