THz Spectroscopy Reveals the Dynamics of Bound Water in Polymer Films

Terahertz (THz) spectroscopy was used to observe adsorbed water structure and dynamics within polymer films. The THz spectra of adsorbed water, as well as deuterated water, within in the nylon films were observed by the continuous measurement of α-nylon during dehydration. The difference spectra clearly show three absorption bands of water molecules, which behave differently between the H
₂
O and D
₂
O. The spectra were assigned using a combination of ab initio molecular dynamics simulations and solid-state density functional theory calculations. The results show that the inclusion of H
₂
O and D
₂
O into polymer films results in a distinct set of spectral features that, while similar in frequencies to the dynamics of bulk water, represent significantly different motions owing to the unique chemical environment within the material.