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.

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 PACMAN PERCOLATION AND THE GLASS TRANSITION

Fractals ◽  
2013 ◽  
Vol 21 (03n04) ◽  
pp. 1350021 ◽  
Author(s):  
RAFFAELE PASTORE ◽  
MASSIMO PICA CIAMARRA ◽  
ANTONIO CONIGLIO
Keyword(s):  
Monte Carlo ◽  
Relaxation Time ◽  
Glass Transition ◽  
Monte Carlo Simulations ◽  
Relaxation Process ◽  
Time Scales ◽  
Relaxation Processes ◽  
Percolation Transition ◽  
Glass Model ◽  
Different Time Scales

We investigate via Monte Carlo simulations the kinetically constrained Kob-Andersen lattice glass model showing that, contrary to current expectations, the relaxation process and the dynamical heterogeneities seems to be characterized by different time scales. Indeed, we found that the relaxation time is related to a reverse percolation transition, whereas the time of maximum heterogeneity is related to the spatial correlation between particles. This investigation leads to a geometrical interpretation of the relaxation processes and of the different observed time scales.

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.

Effect of high pressure on glass transition in Zr-Ti-Cu-Ni-Be bulk metallic glass

2002 ◽  
Vol 754 ◽  
Author(s):  
Wei Hua Wang ◽  
Ping Wen ◽  
Yan Hui Zhao ◽  
Ming Xiang Pan ◽  
De Qian Zhao
Keyword(s):  
High Pressure ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Free Volume ◽  
Bulk Glass ◽  
Free Volume Theory ◽  
Glass Forming

ABSTRACTA new method is developed to directly exhibit glass transition in Zr-Ti-Cu-Ni-Be bulk glass-forming alloy under high pressure in metallic glass. Via the method, we derive an increase of glass transition temperature, Tg with pressure of 5.6 K/GPa, and a formation volume (ΔVf) of 6.5 Å3 for diffusion and the migration volume (ΔVm) of 6.5 Å3. The glass transition under high pressure is simulated based on the free-volume theory, and the simulations are consistent with the experimental observations.

scholarly journals Relaxation Phenomena in Chitosan-Au Nanoparticle Thin Films

Polymers ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 3214
Author(s):  
Elodie Strupiechonski ◽  
Marisa Moreno-Ríos ◽  
Erika O. Ávila-Dávila ◽  
Ramón Román-Doval ◽  
Evgeny Prokhorov ◽  
...  
Keyword(s):  
Thin Films ◽  
Glass Transition ◽  
Relaxation Process ◽  
Disordered Systems ◽  
Chemical Reduction ◽  
Sodium Succinate ◽  
Au Nanoparticle ◽  
Relaxation Processes ◽  
Potential Barriers ◽  
Percolation Effect

Chitosan–gold nanoparticle (CS/AuNP) thin films were synthesized through the chemical reduction of HAuCl4 in sodium citrate/chitosan solutions. The dielectric and dynamic mechanical behaviors of CS/AuNP films have been investigated as a function of moisture and HAuCl4 content. Two relaxation processes in the nanocomposites have been observed. The α-relaxation process is related to a glass transition in wet CS/AuNP films. However, in dry composites (with 0.2 wt% of moisture content), the glass transition vanished. A second relaxation process was observed from 70 °C to the onset of thermal degradation (160 °C) in wet films and from 33 °C to the onset of degradation in dry films. This relaxation is identified as the σ-relaxation and may be related to the local diffusion process of ions between high potential barriers in disordered systems. The α- and σ-relaxation processes are affected by the HAuCl4 content of the solutions from which films were obtained because of the interaction between CS, sodium succinate, and gold nanoparticles. With about 0.6 mM of HAuCl4, the conductivity of both wet and dry films sharply increased by six orders, corresponding to the percolation effect, which may be related to the appearance of a conductivity pathway between AuNPs, HAuCl4, and NaCl.

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