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Ueno N, Sato H. Visualization of isothermal crystallization and phase separation in poly[(R)-3-hydroxybutyrate]/poly(L-lactic acid) by low-frequency Raman imaging. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2024; 312:124052. [PMID: 38394883 DOI: 10.1016/j.saa.2024.124052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2023] [Revised: 01/24/2024] [Accepted: 02/16/2024] [Indexed: 02/25/2024]
Abstract
The visualization of the variation of the inter/intra molecular interaction (C = O⋯CH3) between poly[(R)-3-hydroxybutyrate] (PHB) and poly-L-lactic acid (PLLA) in the PHB/PLLA miscible blend during phase separation and crystallization process was successfully investigated using Raman imaging. Images of the blend were developed using high- and low-frequency Raman spectra acquired during the isothermal crystallization of the blend, and both of them were compared. The low-frequency region allowed to observe the changes in the hydrogen bonds between the molecular chains in the blend during phase separation and crystallization via a band at 75 cm-1 derived from PHB. The imaging results obtained using the band at 75 cm-1 due to hydrogen bonding (C = O⋯CH3) between molecular chains were in good agreement with the results obtained using the C = O stretching band at 1720 cm-1. Herein, we demonstrated that the low-frequency region of the Raman spectrum is more sensitive to detecting the start of the phase separation and crystallization of PHB than the corresponding high-frequency region.
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Affiliation(s)
- Nami Ueno
- Graduate School of Human Development and Environment, Kobe University, Tsurukabuto, Nada-Ku, Kobe 657-8501, Japan
| | - Harumi Sato
- Graduate School of Human Development and Environment, Kobe University, Tsurukabuto, Nada-Ku, Kobe 657-8501, Japan; Molecular Photoscience Research Center, Kobe University, Rokkoudai, Nada-Ku, Kobe 657-8501, Japan.
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2
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Jesionek P, Hachuła B, Heczko D, Lamrani T, Jurkiewicz K, Tarnacka M, Książek M, Kamiński K, Kamińska E. Studies on the nature and pressure evolution of phase transitions in 1-adamantylamine and 1-adamantanol. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2023; 299:122794. [PMID: 37167743 DOI: 10.1016/j.saa.2023.122794] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2023] [Revised: 04/01/2023] [Accepted: 04/26/2023] [Indexed: 05/13/2023]
Abstract
In this paper, several experimental techniques, i.e., differential scanning calorimetry, X-ray diffraction, Fourier transform infrared, Raman, and broadband dielectric spectroscopy were applied to study the nature of the phase transitions in 1-adamantylamine (1-NH2-ADM, C10H17N) and 1-adamantanol (1-OH-ADM, C10H16O). Calorimetric measurements showed one and three endothermic peaks in thermograms for the latter and the former substance, respectively. Indeed, results of spectroscopic investigations indicated that the observed thermal events in 1-NH2-ADM correspond to transitions between various plastic crystal (PC) phases (I, II, III, IV), while the endothermic process in 1-OH-ADM can be assigned to a phase transition between the PC and the ordinary crystal (OC). Especially interesting were the outcomes of dielectric studies carried out both at ambient and high-pressure conditions, during heating and cooling cycles. They showed: i) noticeable changes in the frequency dependencies of the imaginary (ε'') and real (ε') parts of the complex dielectric permittivity that occurred around temperatures of the characteristic endothermic events detected by the calorimetry, and ii) significant fluctuations of ε'' and ε' at pressures attributed to the respective phase transitions. Moreover, the pressure coefficients of the phase transition temperatures were estimated to be approximately equal to 0.2 K/MPa for both compounds. In turn, volume variation (ΔV) at the PC (II)-PC (III) and PC (III)-PC (IV) transition temperatures for 1-NH2-ADM was essentially different than ΔV for the PC-OC transition in 1-OH-ADM.
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Affiliation(s)
- Paulina Jesionek
- Institute of Chemistry, Faculty of Science and Technology, University of Silesia in Katowice, Szkolna 9, 40-007 Katowice, Poland; Department of Pharmacognosy and Phytochemistry, Faculty of Pharmaceutical Sciences in Sosnowiec, Medical University of Silesia in Katowice, Jagiellonska 4, 41-200 Sosnowiec, Poland
| | - Barbara Hachuła
- Institute of Chemistry, Faculty of Science and Technology, University of Silesia in Katowice, Szkolna 9, 40-007 Katowice, Poland.
| | - Dawid Heczko
- Department of Statistics, Department of Instrumental Analysis, Faculty of Pharmaceutical Sciences in Sosnowiec, Medical University of Silesia in Katowice, ul. Ostrogorska 30, 41-200 Sosnowiec, Poland
| | - Taoufik Lamrani
- Institute of Physics, Faculty of Science and Technology, University of Silesia in Katowice, 75 Pulku Piechoty 1, 41-500 Chorzow, Poland
| | - Karolina Jurkiewicz
- Institute of Physics, Faculty of Science and Technology, University of Silesia in Katowice, 75 Pulku Piechoty 1, 41-500 Chorzow, Poland.
| | - Magdalena Tarnacka
- Institute of Physics, Faculty of Science and Technology, University of Silesia in Katowice, 75 Pulku Piechoty 1, 41-500 Chorzow, Poland
| | - Maria Książek
- Institute of Physics, Faculty of Science and Technology, University of Silesia in Katowice, 75 Pulku Piechoty 1, 41-500 Chorzow, Poland
| | - Kamil Kamiński
- Institute of Physics, Faculty of Science and Technology, University of Silesia in Katowice, 75 Pulku Piechoty 1, 41-500 Chorzow, Poland
| | - Ewa Kamińska
- Department of Pharmacognosy and Phytochemistry, Faculty of Pharmaceutical Sciences in Sosnowiec, Medical University of Silesia in Katowice, Jagiellonska 4, 41-200 Sosnowiec, Poland
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Zhu Z, Bian Y, Zhang X, Zeng R, Yang B. Study on the crystallization behavior and conformation adjustment scale of poly(lactic acid) in the terahertz frequency range. Phys Chem Chem Phys 2023; 25:8472-8481. [PMID: 36883295 DOI: 10.1039/d3cp00208j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/09/2023]
Abstract
The observed properties of crystalline polymers are determined by their internal structure, which in turn is the result of their different crystallization behaviors. Here, we investigate the crystallization behavior of poly(lactic acid) (PLA) by terahertz time-domain spectroscopy (THz-TDS) at varied temperatures. We find that the changes in the chain packing and conformation of PLA are characterized by THz spectroscopy. Combining X-ray diffraction (XRD) and infrared spectroscopy (IR), we attributed the blue-shift of the THz peak to the tightness of the chain packing, while its absorption enhancement is caused by the conformation transition. The effects of chain packing and chain conformation on the characteristic peak are phased. Furthermore, absorption discontinuities of the characteristic peaks of PLA crystallized at different temperatures are observed, which originated from differences in the degree of conformational transition caused by different thermal energies. We find that the crystallization temperature at which the absorption mutation of PLA occurs corresponds to the temperature at which the motion of the segment and molecular chain is excited, respectively. At these two temperatures, PLA exhibits different scales of conformational transitions leading to stronger absorption and larger absorption changes at higher crystallization temperatures. The results demonstrate that the driving force of PLA crystallization is indeed from changes in chain packing and chain conformation, and the molecular motion scale can also be characterized by THz spectroscopy.
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Affiliation(s)
- Zhenqi Zhu
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou, 310018, P. R. China.
| | - Yujing Bian
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou, 310018, P. R. China.
| | - Xun Zhang
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou, 310018, P. R. China.
| | - Ruonan Zeng
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou, 310018, P. R. China.
| | - Bin Yang
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou, 310018, P. R. China.
- Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of Education, Zhejiang Sci-Tech University, Hangzhou, 310018, P. R. China
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Liu TY, Xu PY, Lu B, Zhen ZC, Zheng WZ, Dong YC, Li X, Wang GX, Ji JH. Enhanced degradation of poly(ethylene terephthalate) by the addition of lactic acid / glycolic acid: composting degradation, seawater degradation behavior and comparison of degradation mechanism. JOURNAL OF HAZARDOUS MATERIALS 2023; 446:130670. [PMID: 36580787 DOI: 10.1016/j.jhazmat.2022.130670] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2022] [Revised: 12/08/2022] [Accepted: 12/23/2022] [Indexed: 06/17/2023]
Abstract
The degradability improvement of poly(ethylene terephthalate) (PET), one of the most widely used but non-degradable disposable packaging material, is of great significance. However, the balance between degradability and mechanical properties remains a huge challenge. Herein, simple hydroxy acids, lactic acid (LA) and glycolic acid (GA) as easy hydrolysis sites were introduced into non-degradable PET via melt polycondensation. A series of high molecular weight poly(ethylene terephthalate-co-L‑lactide) (PETL) and poly(ethylene terephthalate-co-glycolate) (PETG) copolyesters were synthesized with an excellent tensile strength greater than 50 MPa, much higher than that of most commercially available degradable polymers. The introduction of hydroxy acid endows PET with significantly improved composting and seawater degradation performance. Furtherly, the degradation rate of PETG with hydrophilic GA unit was faster than that of PETL, and the mineralization rate of PETG80 reaches 22.0%. The density of functional theory (DFT) calculation revealed that adding hydroxy acid to the PET molecular chain reduced the energy barrier of the hydrolysis reaction. The molecular polarity index (MPI) analysis furtherly confirmed that the higher affinity between the GA unit and water may be the primary reason for the faster degradation of PETG.
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Affiliation(s)
- Tian-Yuan Liu
- National Engineering Research Center of Engineering Plastics and Ecological Plastics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Peng-Yuan Xu
- National Engineering Research Center of Engineering Plastics and Ecological Plastics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Bo Lu
- National Engineering Research Center of Engineering Plastics and Ecological Plastics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China; Hainan Degradable Plastics Technology Innovation Center, Haikou 571137, China
| | - Zhi-Chao Zhen
- National Engineering Research Center of Engineering Plastics and Ecological Plastics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China; Hainan Degradable Plastics Technology Innovation Center, Haikou 571137, China
| | - Wei-Zhen Zheng
- National Engineering Research Center of Engineering Plastics and Ecological Plastics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yan-Chao Dong
- National Engineering Research Center of Engineering Plastics and Ecological Plastics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xiao Li
- National Engineering Research Center of Engineering Plastics and Ecological Plastics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Ge-Xia Wang
- National Engineering Research Center of Engineering Plastics and Ecological Plastics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China; Hainan Degradable Plastics Technology Innovation Center, Haikou 571137, China.
| | - Jun-Hui Ji
- National Engineering Research Center of Engineering Plastics and Ecological Plastics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China; Hainan Degradable Plastics Technology Innovation Center, Haikou 571137, China.
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Zhu Z, Bian Y, Zhang X, Zeng R, Yang B. Study of Crystallinity and Conformation of Poly(lactic acid) by Terahertz Spectroscopy. Anal Chem 2022; 94:11104-11111. [PMID: 35881498 DOI: 10.1021/acs.analchem.2c02652] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
During crystallization, conformational changes are often accompanied by the formation of interactions. Terahertz (THz) spectroscopy exhibits strong responses to the crystalline poly(lactic acid) (PLA). Therefore, we estimate the relative crystallinity and investigate the effect of conformational transition on the vibration of PLA by THz spectroscopy. By comparing with the results of X-ray diffraction (XRD) and differential scanning calorimetry (DSC), the validity of THz spectroscopy to calculate crystallinity is verified. Furthermore, the peak intensity of PLA at 2.01 THz increases with crystallinity. Combined with Fourier transform infrared spectroscopy (FTIR), the vibrational intensity of PLA at 2.01 THz is highly correlated with the contribution of gt conformation, showing a linear relationship. In addition, the vibrational peak of PLA also reflects the interchain interactions. We believe that the increase in peak intensity with increasing crystallinity originates from the effect of the dipole-dipole interactions between the carbonyl groups. Our study demonstrates the ability of THz spectroscopy to estimate the crystallinity of PLA, and the peak at 2.01 THz shows conformational and interaction sensitivities.
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Affiliation(s)
- Zhenqi Zhu
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou 310018, P. R. China
| | - Yujing Bian
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou 310018, P. R. China
| | - Xun Zhang
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou 310018, P. R. China
| | - Ruonan Zeng
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou 310018, P. R. China
| | - Bin Yang
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou 310018, P. R. China.,Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of Education, Zhejiang Sci-Tech University, Hangzhou 310018, P. R. China
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Bian Y, Wu X, Zhu Z, Zhang X, Zeng R, Yang B. Terahertz spectroscopy for interpreting the formation and hierarchical structures of silk fibroin oligopeptides. Analyst 2022; 147:1915-1922. [PMID: 35364604 DOI: 10.1039/d1an02088a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Determining the configuration and conformation of peptides is crucial for interpreting their structure-property relationships. In this work, we present nondestructive terahertz time-domain spectroscopy combined with density functional theory (DFT) and potential energy distribution (PED) analysis to identify the hierarchical structures of oligopeptides. The characteristic THz spectra of silk fibroin oligopeptides have been measured. Supported by DFT and PED analysis, the intrinsic differences among the dipeptides were identified by the collective vibrational modes of "R" groups and terminal groups linked by molecular chains of amido bonds or benzene rings. For tetrapeptides and hexapeptides, a few weak resonances and intensity differences were distinguished by the vibration mode of the molecular collective network formed by the interaction of amide planes and intramolecular hydrogen bond interactions. According to the THz absorption analyses of amide planes and intramolecular interactions within the molecular chains of silk fibroin oligopeptide isomer pairs, the formation and hierarchical structures were successfully interpreted using THz spectroscopy. This investigation develops a better understanding of the peptide formation mechanism, which further provides guidance in interpreting the formation of silk.
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Affiliation(s)
- Yujing Bian
- Key Laboratory of Advanced Textile Materials and Manufacturing Technology of Ministry of Education, Zhejiang Sci-Tech University, Hangzhou, 310018, Zhejiang, China.
| | - Xiaodong Wu
- Key Laboratory of Advanced Textile Materials and Manufacturing Technology of Ministry of Education, Zhejiang Sci-Tech University, Hangzhou, 310018, Zhejiang, China.
| | - Zhenqi Zhu
- Key Laboratory of Advanced Textile Materials and Manufacturing Technology of Ministry of Education, Zhejiang Sci-Tech University, Hangzhou, 310018, Zhejiang, China.
| | - Xun Zhang
- Key Laboratory of Advanced Textile Materials and Manufacturing Technology of Ministry of Education, Zhejiang Sci-Tech University, Hangzhou, 310018, Zhejiang, China.
| | - Ruonan Zeng
- Key Laboratory of Advanced Textile Materials and Manufacturing Technology of Ministry of Education, Zhejiang Sci-Tech University, Hangzhou, 310018, Zhejiang, China.
| | - Bin Yang
- Key Laboratory of Advanced Textile Materials and Manufacturing Technology of Ministry of Education, Zhejiang Sci-Tech University, Hangzhou, 310018, Zhejiang, China.
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Singh K, Garg D, Bandyopadhyay A, Sengupta A. Dual spectroscopic detection of THz energy modes of critical chemical compounds. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2022; 271:120923. [PMID: 35121475 DOI: 10.1016/j.saa.2022.120923] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2021] [Revised: 01/14/2022] [Accepted: 01/17/2022] [Indexed: 06/14/2023]
Abstract
Precise identification and sensing of organic and inorganic molecular systems are key factors in several applications in present industrial and scientific domains. While high energy modes, due to electronic interactions, are mostly impervious to the initial thermodynamic or chemical conditions, the low energy modes are sensitive to such alterations which makes them suitable for quality control purpose with sensitive spectral identification methods. Here we report for the first time, several low frequency peaks of specific nitrogen-based compounds and their derivatives, using the dual spectroscopic approach of Terahertz Time-Domain Spectroscopy (THz-TDS) and THz Raman Spectroscopy (THz-RS). Two different isomeric molecular systems have also been investigated to assess both the selectivity and specificity of low energy modes in their identification and spectral correlation in terms of molecular interactions. This information of low frequency modes can be utilized readily by pharmaceutical and agri-food industries, chemical engineering and crystal growth communities in identification, detection, quality control and industrial waste management.
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Affiliation(s)
- Khushboo Singh
- Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India
| | - Diksha Garg
- Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India
| | - Aparajita Bandyopadhyay
- Joint Advanced Technology Center - Indian Institute of Technology Delhi, New Delhi 110016, India
| | - Amartya Sengupta
- Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India; School of IT and Electrical Engineering, University of Queensland, Brisbane, QLD 4072, Australia.
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Zhu Z, Bian Y, Zhang X, Zeng R, Yang B. Evaluation of formation and proportion of secondary structure in γ-polyglutamic acid by terahertz time-domain spectroscopy. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2022; 271:120940. [PMID: 35093819 DOI: 10.1016/j.saa.2022.120940] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2021] [Revised: 01/13/2022] [Accepted: 01/19/2022] [Indexed: 06/14/2023]
Abstract
The study of secondary structure is essential for understanding peptides and proteins. Here, we measured the terahertz (THz) spectra of γ-polyglutamic acid (γ-PGA) dominated by α-helix and random coil (RC) respectively. The α-helix has two absorption peaks in the THz region, but no absorption peak is observed in the RC conformation. We believe this is because the hydrogen bonding effect leads to a higher orientation in the helix-dominated γ-PGA. At lower pH, the absorption intensity of γ-PGA increases with the induction time. Similar changes were obtained in the Fourier infrared spectroscopy (FTIR). Through the correlation analysis of THz and IR spectroscopy, it is found that the characteristic peak at 1.2 THz can be used as a sensitive indicator of the intermediate conformation of the α-helical structure. In addition, the transformation of α-helix-RC conformation is related to the peak intensity at 1.99 THz (R2 = 0.991), which preliminarily indicates that terahertz time-domain spectroscopy (THz-TDS) has the potential to become a new effective method for characterizing and evaluating secondary structure.
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Affiliation(s)
- Zhenqi Zhu
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou 310018, PR China
| | - Yujing Bian
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou 310018, PR China
| | - Xun Zhang
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou 310018, PR China
| | - Ruonan Zeng
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou 310018, PR China
| | - Bin Yang
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou 310018, PR China; Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of Education, Zhejiang Sci-Tech University, Hangzhou 310018, PR China.
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9
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Visualization of judgment regions in convolutional neural networks for X-ray diffraction and scattering images of aliphatic polyesters. Polym J 2021. [DOI: 10.1038/s41428-021-00531-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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10
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Nishimae A, Sato H. Study of Co-crystallization and Intermolecular Hydrogen Bondings of Poly(glycolide- co- l-lactide) Copolymers by Terahertz and Low-Frequency Raman Spectroscopy. Macromolecules 2021. [DOI: 10.1021/acs.macromol.1c00561] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Atsushi Nishimae
- Graduate School of Human Development and Environment, Kobe University, 3-11 Tsurukabuto, Nada, Kobe, Hyogo 657-8501, Japan
| | - Harumi Sato
- Graduate School of Human Development and Environment, Kobe University, 3-11 Tsurukabuto, Nada, Kobe, Hyogo 657-8501, Japan
- Molecular Photoscience Research Center, Kobe University, 1-1 Rokkodai, Nada, Kobe, Hyogo 657-8501, Japan
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