“…This coalescence with increasing temperature or bifurcation with decreasing temperature is a well-known phenomenon. However, direct observation in isothermal frequency scans as opposed to isochronal temperature scans is still a rather sparsely documented situation. ,, 15 α process region. Dielectric loss vs log frequency for PEN homopolymer between 383 and 428 K at 5 K intervals.…”
Section: Experimental Results and Phenomenological
Analysis For Glass...mentioning
confidence: 99%
“…As a consequence, it has been very widely studied scientifically. The relation between its physical properties and mechanical, dielectric, and NMR relaxational behavior has been of one the areas of study. − In the completely amorphous state obtained by quenching from the melt PET shows a dielectric relaxation process, α, associated with the glass transition region that is typical of amorphous polymers. In addition, it shows a prominent β subglass process well separated in temperature from the α region.…”
The dielectric loss spectra of poly(ethylene 2,6-naphthylene dicarboxylate) (PEN) and several
copolymers of 2,6-naphthylene dicarboxylic acid and terephthalic acid with ethylene glycol have been
studied over a wide range of frequency and temperature. Previously, Ezquerra, Balta-Calleja, and
Zachmann have reported the presence, in isochronal temperature scans of dielectric loss, of a subglass
process (β*) in PEN homopolymer in addition to the subglass process (β) similar to that in poly(ethylene
terephthalate) (PET). In the present work both the β and β* processes in PEN and PET/PEN copolymers
are resolved and characterized in isothermal frequency scans. It was found that the lower temperature
β loss peak in PEN and the copolymers has a complex or composite frequency domain structure requiring
two Cole−Cole processes in its representation. The β* process in the copolymers is found to shift to higher
frequency isothermally (or lower temperature isochronally) with increasing terephthalic acid content.
Analysis of previous dielectric data for PET shows that its β subglass process is also complex in the log
frequency axis but must be represented by three Cole−Cole processes. The two higher frequency
components are essentially identical to the two Cole−Cole processes making up the β process in PEN.
The third and lowest frequency component is interpreted as of the same origin as the β* process in PEN
and the copolymers but shifted to higher frequency isothermally (or lower temperature isochronally) to
where it overlaps with the β process.
“…This coalescence with increasing temperature or bifurcation with decreasing temperature is a well-known phenomenon. However, direct observation in isothermal frequency scans as opposed to isochronal temperature scans is still a rather sparsely documented situation. ,, 15 α process region. Dielectric loss vs log frequency for PEN homopolymer between 383 and 428 K at 5 K intervals.…”
Section: Experimental Results and Phenomenological
Analysis For Glass...mentioning
confidence: 99%
“…As a consequence, it has been very widely studied scientifically. The relation between its physical properties and mechanical, dielectric, and NMR relaxational behavior has been of one the areas of study. − In the completely amorphous state obtained by quenching from the melt PET shows a dielectric relaxation process, α, associated with the glass transition region that is typical of amorphous polymers. In addition, it shows a prominent β subglass process well separated in temperature from the α region.…”
The dielectric loss spectra of poly(ethylene 2,6-naphthylene dicarboxylate) (PEN) and several
copolymers of 2,6-naphthylene dicarboxylic acid and terephthalic acid with ethylene glycol have been
studied over a wide range of frequency and temperature. Previously, Ezquerra, Balta-Calleja, and
Zachmann have reported the presence, in isochronal temperature scans of dielectric loss, of a subglass
process (β*) in PEN homopolymer in addition to the subglass process (β) similar to that in poly(ethylene
terephthalate) (PET). In the present work both the β and β* processes in PEN and PET/PEN copolymers
are resolved and characterized in isothermal frequency scans. It was found that the lower temperature
β loss peak in PEN and the copolymers has a complex or composite frequency domain structure requiring
two Cole−Cole processes in its representation. The β* process in the copolymers is found to shift to higher
frequency isothermally (or lower temperature isochronally) with increasing terephthalic acid content.
Analysis of previous dielectric data for PET shows that its β subglass process is also complex in the log
frequency axis but must be represented by three Cole−Cole processes. The two higher frequency
components are essentially identical to the two Cole−Cole processes making up the β process in PEN.
The third and lowest frequency component is interpreted as of the same origin as the β* process in PEN
and the copolymers but shifted to higher frequency isothermally (or lower temperature isochronally) to
where it overlaps with the β process.
“…A detailed line shape analysis in the β-relaxation regime was not made. Such an analysis was attempted in dielectric relaxation experiments of poly(ethylene terephthalate) [17]. The experiments are complicated by the fact that poly(ethylene terephthalate) has a high tendency to crystallize, and that a β-peak masks the MCT β-process.…”
We present simulation results for a model polymer melt, consisting of short, nonentangled chains, in the supercooled state. The analysis focuses on the monomer dynamics, which is monitored by the incoherent intermediate scattering function. The scattering function is recorded over six decades in time and for many different wave-vectors which range from the size of a chain to about three times the maximum position of the static structure factor. The lowest temperatures studied are slightly above T c , the critical temperature of mode-coupling theory (MCT), where T c was determined from a quantitative analysis of the β-and α-relaxations. We find evidence for the space-time factorization theorem in the β-relaxation regime, and for the time-temperature superposition principle in the α-regime, if the temperature is not too close to T c . The wave-vector (q-) dependence of the nonergodicity parameter, of the critical amplitude, and the α-relaxation time are in qualitative agreement with calculations for hard spheres. For q larger than the maximum of the structure factor the α-relaxation time τ q already agrees fairly well with the asymptotic MCT-prediction τ q ∼ q −1/b . The behavior of the relaxation time at small q can be rationalized by the validity of the Gaussian approximation and the value of the Kohlrausch stretching exponent, as suggested in neutron-scattering experiments.
“…Reflecting the importance of the semicrystalline polymer poly(ethylene terephthalate) PET, considerable scientific effort has been made to elucidate its properties. The research in connection with PET covers virtually all aspects of polymer physics such as correlation between X-ray structure and force field methods, , dielectric measurements , and their relation to mode coupling theory, crystal structure, the relation between morphology and mechanical properties, − or the characterization of orientation. , Important aspects can be studied by the use of solid-state NMR spectroscopy to determine morphology, , orientation, − and mobility − in the bulk material. Previous solid-state NMR studies concerning mobility were restricted to information deduced from relaxation times or line shape analysis.…”
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