Temperature modulated calorimetry and dielectric spectroscopy in the glass transition region of polymers

Hensel, A.; Dobbertin, J.; Schawe, J.E.K.; Boller, A.; Schick, Christoph

doi:10.1007/bf01983612

Cited by 122 publications

(68 citation statements)

References 28 publications

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“…This peak corresponds to the segmental a relaxation associated with the glass transition. It is well established that, because of the similar range of the equivalent frequency of TSDC and of DSC measurements of about 10 À2 -10 À4 Hz, 30,33 the TSDC a peak is in the temperature region of calorimetric T g . 34 For pure Jeffamine D2000 the TSDC a peak is at about À75 C (inset to Fig.…”

Section: Resultsmentioning

confidence: 98%

Polymer dynamics in rubbery epoxy networks/polyhedral oligomeric silsesquioxanes nanocomposites

Kourkoutsaki

Logakis

Kroutilová

et al. 2009

J of Applied Polymer Sci

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Dielectric techniques, including thermally stimulated depolarization currents (TSDC, À150 to 30 C) and, mainly, broadband dielectric relaxation spectroscopy (DRS, 10 À2 -10 6 Hz, À150 to 150 C) were employed, next to differential scanning calorimetry (DSC), to investigate molecular dynamics in rubbery epoxy networks prepared from diglycidyl ether of Bisphenol A (DGEBA) and poly (oxypropylene)diamine (Jeffamine D2000, molecular mass 2000) and modified with polyhedral oligomeric silsesquioxanes (POSS) units covalently bound to the chains as dangling blocks. Four relaxations were detected and analyzed: in the order of increasing temperature at constant frequency, two local, secondary c and b relaxations in the glassy state, the segmental a relaxation associated with the glass transition and the normal mode relaxation, related with the presence of a dipole moment component along the Jeffamine chain contour. Measurements on pure Jeffamine D2000 helped to clarify the molecular origin of the relaxations observed. A significant reduction of the magnitude and a slight acceleration of the a and of the normal mode relaxations were observed in the modified networks. These results suggest that a fraction of polymer is immobilized, probably at interfaces with POSS, due to constraints imposed by the covalently bound rigid nanoparticles, whereas the rest exhibits a slightly faster dynamics due to increaseof free volume resulting from loosened molecular packing of the chains (plasticization by the bulky POSS units).The increase of free volume is rationalized by density measurements.

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Section: Resultsmentioning

confidence: 98%

Polymer dynamics in rubbery epoxy networks/polyhedral oligomeric silsesquioxanes nanocomposites

Kourkoutsaki

Logakis

Kroutilová

et al. 2009

J of Applied Polymer Sci

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“…DSC heating rate was transformed to an equivalent frequency. 42,43 By fitting logarithm frequency from DSC and DMA with reciprocal glass transition temperature (determined by tan d peak position in DMA), we obtained best fit lines in an Arrhenius plot (not shown in the interest of brevity). The slope of the best fit lines is the activation energy.…”

Section: Mechanical Propertiesmentioning

confidence: 99%

Nanocomposites of poly(vinylidene fluoride) with multiwalled carbon nanotubes

Huang

Edenzon

Fernández

et al. 2009

J of Applied Polymer Sci

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ABSTRACT:The preparation and characterization of nanocomposites of poly(vinylidene fluoride), PVDF, with acid treated multiwalled carbon nanotubes (MWCNT) with a wide composition range, from 0.1 to 5.0% MWCNT by weight, is reported. Effect of uniaxial orientation by zone drawing on these nanocomposites is discussed and compared with unoriented compression molded films. Static room temperature two-dimensional wide angle X-ray scattering and Fourier transform infrared spectroscopy were used for phase identification. Differential scanning calorimetry, polarizing optical microscopy, dynamic mechanical analysis (DMA), and thermogravimetic analysis (TGA) were used to study the thermal and mechanical properties. Incorporation of MWCNT into PVDF has no obvious effect in forming beta phase crystal in the PVDF/ MWCNT bulk films, while zone drawing cause a significant alpha to beta transition in PVDF/MWCNT. Results indicate that MWCNTs act as nucleation agent during crystallization and slightly increase the degree of crystallinity of PVDF/MWCNT bulk films. TGA indicates the thermal stability is improved when MWCNT concentration increases for unoriented PVDF/MWCNT film. The modulus also increases significantly when MWCNT concentration increases. The glass transition temperature measured by the peak position of tand from DMA does not change with MWCNT concentration, but a slightly higher glass transition can be obtained by zone drawing.

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“…For the DSC experiment, such an exact assignment is not possible. From a relationship between cooling rate and relaxation frequency [15,28], a frequency of nearly 10 -3 Hz can be estimated for the thermal glass transition at a cooling rate of 10 K min -1.…”

Section: _ As (5) Asamentioning

confidence: 99%

Dielectric spectroscopy and calorimetry in the glass transition region of semi-crystalline poly(ethylene terephthalate)

Dobbertin

Hensel

Schick

1996

Journal of Thermal Analysis

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120

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Confinement of the glass-forming regions in the nanometer range influences the (x-relaxation which is associated with the glass transition. These effects were investigated for semicrystalline poly(ethylene terephthalate) by dielectric spectroscopy and differential scanning calorimetry. The. results are discussed within the concept of cooperative length, i.e. the characteristic length of the cooperative process of glass transition. Both experiments showed a dependence of the glass transition on the mean thickness of the amorphous layers. For the dielectric relaxation, the loss maximum was found to shift to higher temperatures with decreasing thickness of the amorphous layers, but no differences were observed in the curve shape for the differently crystallized samples. For the calorimetric measurements, in contrast, there was no correlation for the glass transition temperature, whereas the curve shape did correlate with the layer thickness of the mobile amorphous fraction. From the structure parameters, a characteristic length of approximately (2.5+1) nm was estimated for the unconfined glass relaxation (transition).

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Temperature modulated calorimetry and dielectric spectroscopy in the glass transition region of polymers

Cited by 122 publications

References 28 publications

Polymer dynamics in rubbery epoxy networks/polyhedral oligomeric silsesquioxanes nanocomposites

Polymer dynamics in rubbery epoxy networks/polyhedral oligomeric silsesquioxanes nanocomposites

Nanocomposites of poly(vinylidene fluoride) with multiwalled carbon nanotubes

Dielectric spectroscopy and calorimetry in the glass transition region of semi-crystalline poly(ethylene terephthalate)

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