Boson peak dynamics of natural polymer starch investigated by terahertz time-domain spectroscopy and low-frequency Raman scattering

Abstract

Terahertz time-domain spectroscopy and low-frequency Raman scattering were performed on the natural polymer starch to investigate the boson peak (BP) dynamics. In the infrared spectrum, the BP was observed at 0.99THz at the lowest temperature. Compared to the result from a previous study for vitreous glucose, both the frequency of the BP and absorption coefficient show lower values than those of the vitreous glucose. These behaviors originate from the longer correlation length of the medium-range order and lower concentration of hydroxyl groups in the starch. In the Raman spectrum, the BP was observed at 1.1THz at room temperature, although the BP was not observed around room temperature due to the excess wing of the fast relaxation modes in the infrared spectrum. The temperature dependence of ε″(ν) during the heating process and cooling process shows a hysteresis below 230K. During the heating process, kinks were observed at 140K and 230K. These kinks are attributed to the β-relaxation and the β-relaxation, respectively.

Low-energy optical phonons induce glassy-like vibrational and thermal anomalies in ordered crystals

“…In particular, [21] has reported experimental observations of a strong boson peak in perfectly ordered crystals of halomethanes due to low-lying optical modes, whereas [22,23] experimentally observed the upturn of the VDOS predicted here in organic molecular systems with high degree of crystallinity (and presumably very soft optical modes) such as starch and glucose. Similar behaviors have been measured also in thermoelectric crystals [24,25] where a boson peak in the VDOS is also observed, and where, interestingly, low-energy vibrations (so-called rattling) of caged compounds give rise to an upturn in the VDOS at vibrational energies below the boson peak [18].…”

Glass Transition in Rice Pasta as Observed by Combined Neutron Scattering and Time-Domain NMR

“…In consequence, the total neutron cross-section values decrease below the level predicted by the AFGA model. Importantly, changes in the vibrational structure of starch due to changes in the secondary structure and relative crystallinity level have been reported in the literature [ 79 , 80 , 81 , 82 , 83 , 84 , 85 ]. Specifically, for the low-energy modes, terahertz time-domain spectroscopy and low-frequency Raman scattering were performed on the natural polymer starch to investigate the boson peak (BP) dynamics.…”

Non-destructive broadband terahertz spectroscopy for investigating degradation of poly(2-ethylcyanoacrylic) adhesive

“…The lack of observable spectral bands in the low frequency region due to our instrumental setup prevents in-depth discussion of the ne nanostructure of the amorphous structure based on the boson peaks. 11,12 However, we believe that the differences in this region should be considered in further investigations to provide a wider understanding of the curing processes and nanostructures of adhesive polymer materials.…”

“…10 In recent years, the high-order structures of amorphous polymers have also been investigated using boson peak model analysis of the low-frequency region of their THz spectra. 11,12 Adhesive systems undergo polymerisation to become polymer materials. While some THz spectroscopic investigations have been carried out on adhesives under limited conditions, there have been no systematic investigations of adhesives systems and their degradation processes using broadband THz spectroscopy.…”