Observation and Analysis of Molecular Vibration Modes in Polylactide at Terahertz Frequencies

Abstract

Terahertz (THz) spectra were obtained for polylactide, and they were analyzed by numerical calculations based on density functional theory. An absorption band was observed at approximately 50 cm À1 , which becomes larger when the THz electric field is parallel to the sample drawing direction. An absorption peak with a similar directional dependence appears at approximately 40 cm À1 in the simulation, which is due to normalmode molecular vibrations parallel to the molecular helix. Since the 50 cm À1 absorption decreases with an increase in crystallinity and the permittivity shows a step-like decrease, the molecular vibrations responsible for the 50 cm À1 band seem to be subjected to strong damping in amorphous regions. On the other hand, another absorption peak at 65 cm À1 with a positive absorption dependence on the sample's crystallinity is likely to be due to lattice vibration, since it does not appear in the calculations, which only deal with intramolecular vibration.

Terahertz spectral change associated with glass transition of poly-ε-caprolactone

“…It is expected that THz waves provide many pieces of valuable information on various intermolecular vibrations, lattice vibrations, and skeletal vibrations in many substances. [6][7][8][9][10][11] Therefore, THz absorption spectroscopy is useful, especially when we use it in addition to conventional instrumental analyses such as X-ray diffraction (XRD) and infrared (IR) absorption. [9][10][11][12] In recent years, several attempts to measure the glass transition of polymers through the observation of change in free volume of polymer by THz spectroscopy were carried out.…”

“…[6][7][8][9][10][11] Therefore, THz absorption spectroscopy is useful, especially when we use it in addition to conventional instrumental analyses such as X-ray diffraction (XRD) and infrared (IR) absorption. [9][10][11][12] In recent years, several attempts to measure the glass transition of polymers through the observation of change in free volume of polymer by THz spectroscopy were carried out. [13][14][15] In the present paper, we have carried out a basic study aiming at detecting T g of poly-e-caprolactone (PCL, -[(CH 2 ) 5 -COO] n -), a biodegradable polymer widely used in various fields, [16][17][18] by THz spectroscopy.…”

Detection of rust in coated steel plates using terahertz waves

“…Electro-magnetic wave measurement using X-rays, infrared (IR) light, and terahertz (THz) waves offer fast non-contact detection of degradation under opaque materials [1,2]. Especially, THz waves are expected to analyze rust states such as molecular structural changes by applying chemical findings and first-principle calculations [3]. In order to evaluate the applicability of THz waves, the present paper compares experimental results obtained from rust under paints using several kinds of electromagnetic waves as well as those obtained from the impedance measurement, which is one of the promising methods for the rust state estimation [4].…”

Experimental and numerical analyses of molecular vibrations in poly-ε-caprolactone at terahertz frequencies

“…The THz spectroscopy is one of typical such examples. For instance, material analyses using THz spectroscopy have been carried out for many substances such as electrical insulating materials, biodegradable polymers, and western arts [3][4][5][6][7][8][9][10], and relating database websites have been constructed [11]. However, for some substances, analyses of observed spectra have not progressed that far, since their molecular motions in the THz region are very complicated.…”