Interlayer structure, hydrogen-bond, hydration and swelling properties of glycine intercalated layered double hydroxides (LDHs-Gly) were investigated with molecular dynamics (MD) methods. The results show that the interlayer spacing dc increases as hydration level increases. The computed hydration energies reach the most negative values at low water contents and change rapidly over the range 1 = NW = 6, and slowly and gradually approach the potential energy for bulk SPC water at NW > 6. But there are no local minima in the energy over the entire hydration range. This result suggests that LDHs-Gly tend to absorb water continuously in water-rich environments and enhance swelling to delaminate the hydroxide layers. The interlayers of LDHs-Gly exhibit complex hydrogen-bond network. With water content increasing, the glycine molecules progressively change their orientation from parallel to the layers to nearly perpendicular. Water molecules firstly form hydrogen-bond with M-OH layers at low water contents. While the hydroxide layers gradually get to saturation state at Nw > 3. And then water molecules continuously fill the interlayer to expand interlayer spacing.
A molecular dynamics framework to explore the structure and dynamics of layered double hydroxides