Molecular dynamics simulation of anionic clays containing glutamic acid

Supra-molecular structure of glutamic acid intercalated ZnAl layered double hydroxides (Glu–ZnAl–LDH) was modeled by molecular dynamics (MD) methods. Hydrogen bonding, hydration and swelling properties of Glu–LDH have been investigated. For Nw < 8, interlayer spacing dc increased slowly. For Nw ⩾ 8, the variation of dc followed the linear equation dc = 0.432 Nw + 8.837 (R2 = 0.9983). The hydration energy gradually increased as water content increased until Nw = 36. Glu–LDH exhibited a tendency to adsorb water continuously at high water content. Hydration of Glu–LDH occurred as follows: Water molecules initially formed hydrogen bond with layers and anions. When A–W type H-bonds gradually reached a saturation state, water molecules continued to form hydrogen bonds with the hydroxyls of the layers. The L–W type H-bonds gradually substituted the L–A type H-bonds and Glu anions moved to the center of an interlayer and then separated with the layers. Last, a well-ordered structural water layer was formed on the surface hydroxyls of Glu–LDH. The lower releasing content of Glu–LDH maybe was influenced by the lower balance hydration energy and existence of L–A type H-bonds in high water content.