Brill transition of nylon-6 characterized by low-frequency vibration through terahertz absorption spectroscopy

With the aim of opening a route toward new applications of terahertz (THz) spectroscopy to studies of polymer science, the conformations and structural transitions of polycaprolactam (nylon-6) were investigated by THz spectroscopy in the α, γ, pseudo-hexagonal, and amorphous phases. A Brill transition from the α form to the pseudo-hexagonal form was detected at 160 °C from a temperature variation of the peak intensity at 6.6 THz in the second-derivative spectrum of nylon-6. In the amorphous phase, a glass transition was observed at 60 °C, and a new anomaly was found at 110 °C.