Abstract-Exploring the Dynamics of Bound Water in Nylon Polymers with Terahertz Spectroscopy

 Hiromichi Hoshina,  Takuro Kanemura, Chiko Otani, Michael Ruggiero

https://chemrxiv.org/articles/Exploring_the_Dynamics_of_Bound_Water_in_Nylon_Polymers_with_Terahertz_Spectroscopy/10007027

Terahertz (THz) spectroscopy was used to observe adsorbed water structure and dynamics within polymer films, ultimately providing a strong rationale for the observed rates of water desorption. The THz absorption spectra of nylon-6 films undergoes drastic changes during the hydration and drying process. Additionally, the structural change from g to a crystals, induced by the hydration, was observed by the characteristic band of a-nylon-6 at 6.5 THz. Importantly, the THz spectra of adsorbed water, as well as deuterated water, within in the nylon films were observed by the continuous measurement of a-nylon during dehydration. The differential spectra clearly show three absorption bands of water molecules named Peak I, II and III, which behaved differently between the H₂O and D₂O materials. The spectra were assigned using a combination of ab initio molecular dynamics simulations and solid-state density functional theory calculations, and were compared to previous spectral assignments of bulk water. The results show that the inclusion of H₂O and D₂O 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. These results highlight the significant utility of using THz spectroscopy to study the hydration dynamics and spectral signature of bound water in this important class of materials.

Abstract-Correlation Between Saturated Fatty Acid Chain-Length and Intermolecular Forces Determined with Terahertz Spectroscopy

 Shuting Fan,  Michael Ruggiero,  Zhengfang Qian,  Vincent P. Wallace

https://chemrxiv.org/articles/Correlation_Between_Saturated_Fatty_Acid_Chain-Length_and_Intermolecular_Forces_Determined_with_Terahertz_Spectroscopy/7553054

We measured crystalline (C-form) saturated fatty acids with even carbon numbers ranging from 12 to 20 using temperature dependent terahertz time-domain spectroscopy (THz-TDS). Absorption features between 0.5 to 2.75 THz were identified at temperatures from 96 K to 293 K, and a systematic red-shift was observed with the increasing carbon chain length. The origins of these absorption bands were uncovered using state-of-the-art ab initio density functional theory (DFT) calculations. Similar vibrational motions in the absorption bands of the different materials highlight the unique role that THz-TDS has for probing weak non-covalent interactions in these materials. Our results showcase the utility of the terahertz region, which is beyond the scope of related vibrational techniques, providing direct evidence of the effect of chain length on the intermolecular interactions of these molecules.