scholarly journals EXPLORING RELATIONSHIP BETWEEN LOCAL DYNAMICS AND RELAXATION PROCESSES ON THE TERAHERTZ FREQUENCIES IN POLYMERS WITH HYDROGEN BONDS

2021 ◽  
pp. 109-118
Author(s):  
Валерий Александрович Рыжов
Keyword(s):  
Glass Transition ◽  
Hydrogen Bonds ◽  
Low Frequency ◽  
Far Infrared ◽  
Polyamide 6 ◽  
Relaxation Processes ◽  
Temperature Dependent ◽  
Disordered Solids ◽  
Common Features ◽  
Terahertz Frequencies

На терагерцовых частотах либрационно-колебательное движение связано с диэлектрической релаксацией в неупорядоченных твердых телах с водородными связями. Взаимодействие между этими процессами ещё мало изучено, особенно при температурах ниже температуры стеклования, что особенно существенно для молекулярной подвижности в полимерах. Изучены полимеры с водородными связями (полиамид-6 и поливинилхлорид) при температурах от 90 до 4000К в диапазоне 0,25 - 4 ТГц с использованием дальней ИК-спектроскопии. Три общих особенностей наблюдались в спектре диэлектрических потерь, Ɛ"(ν):(а) при температурах значительно ниже стеклования (T) эти потери представлены низкочастотным крылом пика поглощения, обусловленного либрацией мономерных звеньев полимеров. (б) При 0.7 T < T < T наблюдаются дополнительные температурно-зависимые потери, которые могут быть связаны с проявлением вторичных релаксационных процессов. (с) При температурах выше T преобладающим вкладом в терагерцовые потери становятся первичные процессы α-релаксации. Полученные результаты показывают, что эволюция терагерцовых потерь с температурой вызвана изменением структуры водородных связей, которое, по-видимому, является универсальным для систем с подобными межмолекулярными взаимодействиями At terahertz frequencies, torsional-vibrational motion is associated with dielectric relaxation in disordered solids with hydrogen bonds. The interaction between these processes has not been studied much, especially at temperatures below the glass transition temperature, which is especially important for molecular mobility in polymers. Polymers with hydrogen bonds (polyamide-6 and polyvinyl chloride) were studied at temperatures from 90 to 4000 K in the range 0.25 - 4 THz using far-infrared spectroscopy. Three common features were observed in the spectrum of dielectric losses, Ɛ"(ν):(А)at temperatures well below glass transition (T), these losses are represented by the low-frequency wing of the absorption peak due to libration of the monomer units of the polymers. (B) At 0.7 T < T < T , additional temperature-dependent losses are observed, which may be associated with the manifestation of secondary relaxation processes. (C) At temperatures above T, the primary relaxation processes become the dominant contribution to terahertz losses. The results show that the evolution of terahertz losses with temperature is caused by a change in the structure of hydrogen bonds, which, apparently, is universal for systems with similar intermolecular interactions.

Past Results and Future Prospects of the Far-Infrared Studies of Hydrogen Bonding

1968 ◽  
Vol 22 (6) ◽  
pp. 641-649 ◽  
Author(s):  
R. J. Jakobsen ◽  
J. W. Brasch ◽  
Y. Mikawa
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Hydrogen Bonds ◽  
Low Frequency ◽  
Far Infrared ◽  
Future Prospects ◽  
The Past ◽  
Ir Studies ◽  
Infrared Studies ◽  
Order Of Magnitude

In the past five years the number of papers concerned with far-ir studies of hydrogen bonding has increased by an order of magnitude. The results of some of these papers are presented in this review. Most of this work is concerned with the assignment of low frequency hydrogen bond vibrations. Since the major problem is reliable assignments, we discuss techniques used in making the assignments and emphasize the past work in which attempts have been made to substantiate those assignments. These assignments are discussed in terms of the different hydrogen bond vibrations associated with various types of hydrogen bonds. The main needs for future far ir hydrogen bond studies are listed.

Insights into the Structural Dynamics of PLGA at Terahertz Frequencies

2018 ◽  
Author(s):  
Talia A. Shmool ◽  
J. Axel Zeitler
Keyword(s):  
Glass Transition ◽  
Relaxation Process ◽  
Free Volume ◽  
Variable Temperature ◽  
Dipole Moments ◽  
Relaxation Processes ◽  
Segmental Motion ◽  
Terahertz Time Domain Spectroscopy ◽  
Free Volume Theory ◽  
Terahertz Frequencies

The mechanical properties of an amorphous copolymer are directly related to the dynamic processes occurring at the molecular level. Poly lactic-co-glycolic acid (PLGA) is a biodegradable co-polymer, and in this work we investigate the dynamics of PLGA and its glass transition behaviour by performing variable temperature terahertz time-domain spectroscopy (THz-TDS) experiments. We correlate PLGA dynamics, as measured at terahertz frequencies, their temperature dependence, molecular weight (MW), lactide to glycolide ratio, and free volume. The THz-TDS data can be used to detect two distinct glass transition processes, T<sub>g,α</sub> and T<sub>g,β</sub>. To complement our analysis, we use dynamic mechanical analysis (DMA) to probe the β- and α-relaxation processes in PLGA, and compare the results obtained from the DMA experiments with those obtained using THz-TDS. We attribute T<sub>g,β</sub> to the change in dipole moments associated with the β-relaxation process, originating from the local rotation of C-O macromolecular chain segments, and T<sub>g,α</sub> to the change in dipole moments due to large segmental motion of the copolymer backbone associated with the α-relaxation process. We connect our experimental results to the free volume theory proposed by Fox and Flory, and demonstrate our results are consistent with the relationship between the experimentally determined T<sub>g,β</sub> and T<sub>g,α</sub> and free volume and PLGA dynamics.

Anisotropy in the Far Infrared Conductivity of Magnetically-Oriented YBa2Cu3O7-δ Between 50–300K

1989 ◽  
Vol 169 ◽  
Author(s):  
F. Lu ◽  
C.H. Perry ◽  
K. Chen ◽  
R.S. Markiewicz
Keyword(s):  
Energy Gap ◽  
Low Frequency ◽  
Far Infrared ◽  
Free Carrier ◽  
Low Energy ◽  
Phonon Modes ◽  
Temperature Dependent ◽  
Insulating Material ◽  
Gap Anisotropy ◽  
Reflectance Data

AbstractThe far infrared reflectance of magnetically-oriented YBa2Cu3O7-δ has been measured from 30–600 cm-1 over the temperature range 300–50 K. A strongly temperature dependent optical anisotropy is observed in this region. The low energy Ē⊥c spectrum displays a high reflectivity associated with the dominant free carrier contribution. Peaks corresponding to phonons are present in the spectrum associated with the direction perpendicular to the high conductivity Cu - O planes. However the reflectivity for Ē∥c is not characteristic of an insulating material but rather shows a metallic-like rise with decreasing photon energy. The plasma frequencies for both polarizations, obtained from fits to the reflectance data, decrease with decreasing temperature. There is some evidence in the parallel conductivity data taken below Tc, for the onset of an energy gap that is substantially smaller than that deduced for the in-plane value; such a result suggests a large gap anisotropy. The parameters describing a number of low frequency phonon modes for Ē∥c have been determined from fits to the R∥ data. Most show a slight softening as Tc is traversed.

scholarly journals Intermolecular vibrational modes of crystalline Poly-(r)-3-Hydroxybutyrate observed at Terahertz frequencies investigated by molecular dynamics

2020 ◽  
Vol 26 (2) ◽  
pp. 21-31
Author(s):  
Md Khorshed Alam ◽  
Md Saif Ishtiaque ◽  
Md Imran Hossain ◽  
Hiromitsu Takaba
Keyword(s):  
Molecular Dynamics ◽  
Hydrogen Bonds ◽  
Absorption Spectra ◽  
Md Simulation ◽  
Vibrational Transition ◽  
Vibrational Modes ◽  
Temperature Dependent ◽  
Terahertz Frequencies ◽  
Thz Absorption ◽  
Oriented Parallel

Terahertz (THz) absorption spectra of poly 3-hydroxyalkanoates (PHB) for different conformations were investigated using molecular dynamics (MD) method. Temperature-dependent THz absorption spectra of PHB were measured over a temperature range of 10 K to 200 K. Peaks around (2.4-2.6THz) and (3.1-3.2THz) were observed due to vibrational transition of PHB, 1stpeaks are polarized perpendicular to c(┴)axis (along a, b axis) and next peaks are oriented parallel to the c(//) axis. The peak around (2.4-2.6THz) was assigned due to vibrational transition of PHB and C-H…O=C hydrogen bonds are oriented perpendicular to the c(┴) axis. We have also investigated orientation of the intermolecular hydrogen bonds by MD simulation and confirmed that it was mainly along the b axis of PHB. THz absorption spectra shifted to the lower frequencies and noticed widening of the absorption peaks that visualized from characteristics of peaks within creasing temperature, which is well reproduce of experimental observation. Bangladesh Journal of Physics, 26(2), 21-31, December 2019

Insights into the Structural Dynamics of PLGA at Terahertz Frequencies

2018 ◽  
Author(s):  
Talia A. Shmool ◽  
J. Axel Zeitler
Keyword(s):  
Glass Transition ◽  
Relaxation Process ◽  
Free Volume ◽  
Variable Temperature ◽  
Dipole Moments ◽  
Relaxation Processes ◽  
Segmental Motion ◽  
Terahertz Time Domain Spectroscopy ◽  
Free Volume Theory ◽  
Terahertz Frequencies

The mechanical properties of an amorphous copolymer are directly related to the dynamic processes occurring at the molecular level. Poly lactic-co-glycolic acid (PLGA) is a biodegradable co-polymer, and in this work we investigate the dynamics of PLGA and its glass transition behaviour by performing variable temperature terahertz time-domain spectroscopy (THz-TDS) experiments. We correlate PLGA dynamics, as measured at terahertz frequencies, their temperature dependence, molecular weight (MW), lactide to glycolide ratio, and free volume. The THz-TDS data can be used to detect two distinct glass transition processes, T<sub>g,α</sub> and T<sub>g,β</sub>. To complement our analysis, we use dynamic mechanical analysis (DMA) to probe the β- and α-relaxation processes in PLGA, and compare the results obtained from the DMA experiments with those obtained using THz-TDS. We attribute T<sub>g,β</sub> to the change in dipole moments associated with the β-relaxation process, originating from the local rotation of C-O macromolecular chain segments, and T<sub>g,α</sub> to the change in dipole moments due to large segmental motion of the copolymer backbone associated with the α-relaxation process. We connect our experimental results to the free volume theory proposed by Fox and Flory, and demonstrate our results are consistent with the relationship between the experimentally determined T<sub>g,β</sub> and T<sub>g,α</sub> and free volume and PLGA dynamics.

scholarly journals Tetragonal–Cubic Phase Transition and Low-Field Dielectric Properties of CH3NH3PbI3 Crystals

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4215
Author(s):  
Roxana E. Patru ◽  
Hamidreza Khassaf ◽  
Iuliana Pasuk ◽  
Mihaela Botea ◽  
Lucian Trupina ◽  
...  
Keyword(s):  
Dielectric Properties ◽  
Current Knowledge ◽  
Cubic Phase ◽  
Relaxation Processes ◽  
Temperature Dependent ◽  
Thermally Activated ◽  
Low Field ◽  
Conduction Mechanisms ◽  
Temperature Ranges ◽  
Nyquist Plots

The frequency and temperature dependence of dielectric properties of CH3NH3PbI3 (MAPI) crystals have been studied and analyzed in connection with temperature-dependent structural studies. The obtained results bring arguments for the existence of ferroelectricity and aim to complete the current knowledge on the thermally activated conduction mechanisms, in dark equilibrium and in the presence of a small external a.c. electric field. The study correlates the frequency-dispersive dielectric spectra with the conduction mechanisms and their relaxation processes, as well as with the different transport regimes indicated by the Nyquist plots. The different energy barriers revealed by the impedance spectroscopy highlight the dominant transport mechanisms in different frequency and temperature ranges, being associated with the bulk of the grains, their boundaries, and/or the electrodes’ interfaces.

Far Infrared Group Frequencies. V. Oximes and Aldoximes

1973 ◽  
Vol 27 (1) ◽  
pp. 22-26 ◽  
Author(s):  
S. M. Craven ◽  
F. F. Bentley ◽  
D. F. Pensenstadler
Keyword(s):  
Hydrogen Bond ◽  
Infrared Spectra ◽  
Low Frequency ◽  
Far Infrared ◽  
Torsional Vibrations ◽  
Lattice Vibrations ◽  
Dilute Solutions ◽  
Solid Samples ◽  
Bending Modes ◽  
Bond Stretch

The low frequency infrared spectra from 450 to 75 cm−1 of seven oximes and five aldoximes have been recorded for pure samples and for dilute solutions in cyclohexane. An intense characteristic band is present in the solution spectra at 367 ± 10 cm−1. This characteristic band shifts to 275 ± 10 cm−1 in the spectra of the OD compounds. The 367 ± 10 cm−1 and 275 ± 10 cm−1 bands are assigned to OH and OD torsional vibrations. A comparison of the solution spectra with spectra of the solid samples indicated that the OH … N hydrogen bond stretch of oximes and aldoximes occurs in 300 to 200 cm−1 region. Strong bands also are present in 140 to 100 cm−1 region which are due to OH … N bending modes or perhaps lattice vibrations.

Sign in / Sign up

Export Citation Format

Share Document