Intercalation Mechanism and Interlayer Structure of Hexadecylamine inside Layered $\alpha$-Zirconium Phosphates

Well-defined intercalated structure, either interdigitated layers or bilayers, of hexadecylamines (HDAs) in a confined space of a highly-functionalized layered material, $\alpha$- zirconium phosphate ($\alpha$-ZrP), was prepared using two-step intercalation mechanism and these two distinct intercalated structures can serve as model systems to investigate the interaction of the two monolayers whose amphiphilic tails are adjacent to each other. Interlayer structure of HDAs in $\alpha$- ZrP intergallery was characterized with XRD and TEM, and an intriguing two-step deintercalation behaviors of intercalated HDAs were observed with TGA and in-situ SAXS experiments during heating. This deintercalation behaviors are believed to be due to two different interaction force of intercalated HDAs (i.e., electrostatic interaction between host and guest molecule, and hydrophobic interaction between guest molecules) and this interaction force is found to affect interlayer structure of intercalated HDAs. We also found that the thermal hysteresis for the amphiphilic HDA molecules attached to confined geometries is stronger for the interdigitated layers, which is in reasonably good agreement between DSC and SAXS experiments.