Characterizing polymorphism and crystal transformation of polylactide by terahertz time-domain spectroscopy

The Necessity of Periodic Boundary Conditions for the Accurate Calculation of Crystalline Terahertz Spectra

“…As such, terahertz spectroscopy becomes an immensely useful tool for the characterization crystalline materials, rivaling X-ray diffraction in some cases, and surpassing X-ray diffraction in acquisition time. 23,[25][26][27]91 But while he ability of terahertz vibrational spectroscopy to characterize weak forces and complex dynamics in crystals is one of its most significant assets, it simultaneously leads to its most unfortunate aspects, namely, difficulties in interpreting and assigning the experimental spectra. As mentioned, each individual solid exhibits a unique terahertz spectrum, governed by a complex combination of forces, which ultimately does not result in any functional/structural-motif-specific vibrations or trends, unlike in the mid-IR.…”

“…Over the last decade, methods for assigning and interpreting terahertz spectra have advanced significantly, in line with the growing use of terahertz spectroscopy, providing significant insight into many condensed phase phenomena. 5,[20][21][22][23][24][25][26][27][28] For example, the determination of low-frequency vibrations in organic semiconductors, in tandem with experimental terahertz spectra, has enabled a more thorough understanding of the effect of lowfrequency vibrations on charge carrier mobilities in these materials. 15,16 However, such insight is entirely dependent upon the correct prediction of both the vibrational frequencies as well as the associated mode-types, which is fundamentally related to the ability of the simulations to reconstruct the potential energy hy-persurface to a level of accuracy that enables a proper determination of the weak forces responsible for terahertz dynamics.…”

Characterizing the Structure and Phase Transformation of Poly(ethylene Oxide)–Urea Complexes Using Terahertz Time-Domain Spectroscopy

“…[1][2][3] Among them, THz spectroscopy has been reported to show specific responses to the intermolecular modes in hydrogen-bonded networks of various polymeric systems. [4][5][6][7][8] For example, Hoshina et al had suggested that the THz absorption peak at 2.49 THz of poly(R-3-hydroxybutyrate) (PHB) to the intermolecular hydrogen bonding interaction; 4,9 furthermore, they demonstrated that the CÀHÁÁÁO¼C hydrogen bonds are initially formed before establishment of well-defined crystal structures using twodimensional correlation THz spectroscopy. 10 Fischer et al proved that the THz spectral features of DNA is dominated by discrete vibrations mainly associated with the intermolecular motion between individual nucleosides held together by hydrogen bonds; and the hydrogenbonded sheets stack in the c-direction.…”

“…5 Recently, we have proved that THz spectroscopy is an alternative and highly sensitive method to identify the stereocomplex crystals of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) from the homocrystals based on the strong absorption peak at 1.43 THz, which could be assigned to the collective vibration of L-lactic unit and D-lactic unit pairs connecting by hydrogen bonds. 6 By analogy, THz spectroscopy might also have the potential to be of benefit for studying complexes formed between polymers and small molecules through hydrogen bonding interactions.…”

Internal Status of Visibly Opaque Black Rubbers Investigated by Terahertz Polarization Spectroscopy: Fundamentals and Applications

“…In particular, the terahertz time-domain spectroscopy (THz-TDS) based on ultrafast pulsed lasers has been widely used, because of its characteristic feature which allows us to directly obtain spectroscopic information for the complex refractive index, that is, the complex dielectric functions and conductivity. Thus, many terahertz applications involving polymers have been developed; the fingerprint spectroscopy [29], the differentiation between the enantiomer and stereo-complex [30], the determination of the glass transition temperature [31] and the monitoring of the phase transition [26,32,33]. Very recently, the polarization-sensitive (PS) THz-TDS has attracted interest from the viewpoints of both fundamental research [34,35,36,37,38,39,40] and potential terahertz applications [41,42,43,44].…”