Low-frequency vibrational mode anomalies and glass transition: Thermal stability, phonon scattering, and pressure effects

2008 ◽  
Vol 78 (9) ◽  
Author(s):  
Gerardo G. Naumis ◽  
Hugo M. Flores-Ruiz
Keyword(s):  
Thermal Stability ◽  
Glass Transition ◽  
Phonon Scattering ◽  
Vibrational Mode ◽  
Low Frequency ◽  
Pressure Effects

A Raman study of B203 through the liquid-glass transition range

1992 ◽  
Vol 02 ◽  
pp. C2-265-C2-270
Author(s):  
A. K. HASSAN ◽  
L. M. TORELL ◽  
L. BORJESSON
Keyword(s):  
Glass Transition ◽  
Correlation Length ◽  
Room Temperature ◽  
Vibrational Mode ◽  
Low Frequency ◽  
Boson Peak ◽  
Transition Range ◽  
Structural Correlation ◽  
Raman Study ◽  
Correlation Range

The low frequency Raman spectrum of B203 and the boroxol ring vibrational mode at 808 cm-1 have been studied from room temperature to 1273 K as the glass transforms to a melt. Both the low frequeney "boson" peak and the boroxol mode are markedly influenced by the glass transition. Raising the temperature above Tg the strength of the 808 cm-1 mode decreases linearly indicating the Similar behavior of the boroxol ring concentration. The boson peak shows a different temperature behavior, which mirrors that of the sound velo city. The structural correlation length demostrates the same correlation range in the liquid and the glass. The results, when compared with neutron diffraction measurements contradict a recently proposed relation between the "boson correlation length" and the position of the first sharp diffraction peak of the structure factor.

Investigating the role of GeO2 in enhancing the thermal stability and proton mobility of proton-conducting phosphate glasses

2021 ◽  
Author(s):  
Takahisa Omata ◽  
Aman Sharma ◽  
Takuya Kinoshita ◽  
Issei Suzuki ◽  
Tomohiro Ishiyama ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Phosphate Glasses ◽  
Proton Mobility ◽  
Proton Conducting

In this study, the effect of GeO2 on the thermal stability and proton mobility (μH) of proton-conducting phosphate glasses was experimentally investigated using 22HO1/2−3NaO1/2−(12−x)LaO3/2−xGeO2−63PO5/2 glasses. Increasing glass transition temperature (Tg)...

The effect of methyl and methoxy substituents on dianilines for a thermosetting polyimide system

2020 ◽  
Vol 32 (7) ◽  
pp. 801-822 ◽  
Author(s):  
John J La Scala ◽  
Greg Yandek ◽  
Jason Lamb ◽  
Craig M Paquette ◽  
William S Eck ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Molecular Weight ◽  
Glass Transition ◽  
Elevated Temperature ◽  
Methyl Substituent ◽  
Glass Transition Temperatures ◽  
High Performing ◽  
Methoxy Substituent ◽  
Acidic Conditions ◽  
Thermal Stability Of

4,4′-Methylenedianiline (MDA) is widely used in high-temperature polyimide resins, including polymerization of monomer reactants-15. The toxicity of MDA significantly limits the manufacturability using this resin. Modifying the substitution and electronics of MDA could allow for the reduction of toxicity while maintaining the high-performing properties of the materials derived from the modified MDA. The addition of a single methyl substituent, methoxy substituent, location of these substituents, and location of the amine relative to the phenolic bridge were modified as were other non-aniline diamines. Various anilines were condensed with paraformaldehyde under acidic conditions to yield dianilines. These dianilines and diamines were reacted with nadic anhydride and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride in methanol to form the polyamic acid oligomers and heated at elevated temperature to form polyimide oligomers. It was found that the molecular weight of the oligomers derived from MDA alternatives was generally lower than that of MDA oligomers resulting in lower glass transition temperatures ( T gs) and degradation temperatures. Additionally, methoxy substituents further reduce the T g of the polymers versus methyl substituents and reduce the thermal stability of the resin. Methyl-substituted alternatives produced polyimides with similar T gs and degradation temperatures. The toxicity of the MDA alternatives was examined. Although a few were identified with reduced toxicities, the alternatives with properties similar to that of MDA also had high toxicities.

Thermal stability, decomposition and glass transition behavior of PANI/NiO composites

2009 ◽  
Vol 98 (2) ◽  
pp. 533-537 ◽  
Author(s):  
Yanni Qi ◽  
Jian Zhang ◽  
Shujun Qiu ◽  
Lixian Sun ◽  
Fen Xu ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Glass Transition ◽  
Transition Behavior

Donor-acceptor complexes formed by perfluoro-organo bromides and iodides with nitrogenous and other bases. II. Band shapes and widths in the absorption spectrum of gaseous CF3I-N(CH3)3

1971 ◽  
Vol 24 (12) ◽  
pp. 2493 ◽  
Author(s):  
A Mishra ◽  
ADE Pullin
Keyword(s):  
Vibrational Mode ◽  
Low Frequency ◽  
Molecular Complexes ◽  
Wave Number ◽  
Centrifugal Distortion ◽  
Band Shape ◽  
Gaseous Mixtures ◽  
Factors Affecting ◽  
Donor Acceptor ◽  
Vibration Rotation

The absorption band centred at c. 77 cm-1 in gaseous mixtures of CF3I and N(CH3)3 previously reported and attributed to the N-I stretching mode of the complex CF3I-N(CH3)3 has been carefully re-examined. This band is of interest as an example of a low frequency ?dissociative type? vibrational mode of a weak molecular complex. The band is asymmetric and apparently structureless with a half intensity width at room temperature of 28-30 cm-1. The width of the band may be accounted for as arising from transitions vi + vi+1 where vi is the vibrational quantum number of the N-I stretching mode with vi up to c. 10 making appreciable contribution to the intensity on the low wave-number side. Centrifugal distortion in the complex is considered. Centrifugal stretching and consequent weakening of the bond may shift the band envelope 2-3 cm-1 to lower wave numbers. Assessment of these and other factors affecting the band shape suggest that the fundamental frequency is probably c. 90 cm-1. The band shape of the vibrational mode of the complex at c. 272 cm-1 is briefly discussed. Many of the considerations presented in this paper should apply to vibration-rotation band shapes in other weak molecular complexes. Some general consequences of anharmonicity for the interpretation of the spectra of weak molecular complexes are discussed.

Sign in / Sign up

Export Citation Format

Share Document