Low-Frequency Vibrational Modes of Nylon 6 Studied by Using Infrared and Raman Spectroscopies and Density Functional Theory Calculations

• DOI: 10.1021/acs.jpcb.9b04347
• Publication Date: 2019-06-12T19:20:43Z
• Authors: Shigeki Yamamoto; Erika Ohnishi; Harumi Sato; Hiromichi Hoshina; Daitaro Ishikawa; Yukihiro Ozaki
• Keywords: Methylene; Amide

Far-infrared (FIR) and low-frequency Raman bands in the 90–400 cm–1 region of crystalline nylon 6 α form were assigned based on comparisons experimental spectra quantum mechanical calculations. A fragment methodology was applied calculations for explicit consideration interchain interactions crystal symmetry. The main features both FIR reproduced well, which enabled band assignments density functional theory significant improvement conventional there had been a big dispute. Temperature dependence has revealed that at 222 111 are characteristic α-form structure. Their intensities linearly decreased with increasing temperature marked two transition points, correspond to glass Brill transitions. Both can be indicators lattice length 6. On basis calculations, ∼100 successfully methylene torsion transverse motion amide groups NH O atoms move out plane. Decomposition calculated mainly originate from only secondarily groups. Moreover, nearly perfectly governed by groups, could reason why this is particularly sensitive hydrogen bonds among bands. contain perpendicular motions This will their sensitivity Contrarily, 294 parallel polarization chain direction deformation C–CH2–CH2 bending C═O not structural transitions Our previous works regions 125 70 cm–1, specific vibrational peaks polyesters primarily arising out-of-plane ester We find similarity between polymers show around 100 polymer chains.