Crystallinity of poly(ethylene naphthalate) and its relation to terahertz absorption

The crystallinity of poly(ethylene naphthalate) (PEN) was changed by thermal annealing and its effects on terahertz absorption spectra and X-ray diffraction patterns were examined. As a result, the intensity of a relatively sharp absorption peak at around 2.2 THz was found to be proportional to the crystallinity. As a plausible cause of this absorption, a lattice vibration, a torsional vibration, or their combination mode associated with (010) planes in crystal a of PEN is proposed. Therefore, the crystallinity of PEN can be estimated from the intensity of this absorption. (c) 2017 The Japan Society of Applied Physics