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  • 1
    ISSN: 1435-1536
    Keywords: Key words Temperature modulated differential scanning calorimetry ; heat capacity ; glass transition ; relaxation ; polystyrene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  The temperature modulated differential scanning calorimetry (TMDSC) technique can be used for heat capacity spectroscopy in the low frequency range. Measured property is the complex heat capacity C *=C′−iC″. The frequency dependent relaxation transition measured by TMDSC occurs in the temperature range of the thermal glass transition. Thus, the non-equilibrium of the glassy state influences the TMDSC curves. An experimental evidence is the dependence of the shape of the C′-curve on the thermal history. A theoretical description of the influence of the non-equilibrium state on the spectroscopic curves is presented. This description is based on the Tool–Narayanaswamy–Moynihan model.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-8943
    Keywords: melting ; polymers ; signal analysis ; TMDSC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The measured signal of the temperature-modulated differential scanning calorimetry (TMDSC) is discussed in the case of polymer melting. The common data evaluation procedure of TMDSC-signals is the Fourier analysis. The resulting information is the amplitude and the phase shift of the first harmonic of the periodic heat flow component. It is shown that this procedure is not sufficient for quantitative discussions if deviations from the symmetric curve shape occur in the measured heat flow curves. For polymer melting it is demonstrated that asymmetric curves will be measured if the experimental temperature amplitude is too large. In this paper a data evaluation method is presented, which is based on the Fourier transform of the measured curves. The peaks of the first and second harmonics in the resulting spectra are used for the analysis of the asymmetry of the measured curves. In the case of polymer melting this analysis yields the maximum temperature amplitude which follows a correct linear data evaluation. This maximum temperature amplitude depends on the material.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1572-8943
    Keywords: calorimetry ; dielectric ; glass transition ; modulated DSC ; polymers ; relaxation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The results from temperature modulated DSC in the glass transition region of amorphous and semicrystalline polymers are described with the linear response approach. The real and the imaginary part of the complex heat capacity are discussed. The findings are compared with those of dielectric spectroscopy. The frequency dependent glass transition temperature can be fitted with a VFT-equation. The transition frequencies are decreased by 0.5 to 1 orders of magnitude compared to dielectric measurements. Cooling rates from standard DSC are transformed into frequencies. The glass transition temperatures are also approximated by the VFT-fit from the temperature modulated measurements. The differences in the shape of the curves from amorphous and semicrystalline samples are discussed.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1572-8943
    Keywords: cold crystallization ; DSC ; heat capacity ; modulated temperature DSC ; poly(ethylene terephtalate)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The modulated temperature differential scanning calorimetric method (MT-DSC) yields three temperature dependent signals, an underlying heat capacity curve from the underlying heat flow rate (corresponding to the conventional DSC signal), and a complex heat capacity curve with a real part (storage heat capacity) and an imaginary part (loss heat capacity). These curves have been measured in the cold crystallization region for poly(ethylene terephtalate) with a modified Perkin-Elmer DSC-7. The underlying curve shows the well known large exothermic crystallization peak. The storage heat capacity shows a step change which reproduces the change in heat capacity during crystallization. This curve may be used as baseline, to separate the crystallization heat flow rate from the underlying heat flow rate curve. The loss heat capacity curve exhibits a small exothermic peak at the temperature of the step change of the storage curve. It could be caused by changes of the molecular mobility during crystallization.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1572-8943
    Keywords: glass transition ; metallic glass ; silicate glass ; temperature-modulated DSC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The glass transitions of different materials (a silicate glass, a metallic glass, a polymer, a low molecular liquid crystal and a natural product) were investigated. By means of the temperature-modulated DSC (TM-DSC) mode, the frequency was varied. In the case of DSC, the cooling rate was changed. TM-DSC was shown to be a practicable tool for the acquisition of dynamic parameters of glass transitions for all kinds of materials.
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  • 6
    ISSN: 1572-8943
    Keywords: expansivity ; fibers ; modulus ; shrinkage ; temperature calibration ; temperature modulation ; thermomechanical analysis ; TMA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The thermal behavior of a drawn PET fiber has been investigated by thermomechanical analysis, TMA, and by differential scanning calorimetry, DSC. Above the glass transition temperature of 79°C, the fiber shrinks to a maximum of 8% of the initial length. Temperature modulated TMA enabled the separation of the thermal expansion from the overlapping shrinkage during the first heating and to calculate the expansivity, αe and the shrinkage coefficient, αs, independent of each other. Young's modulus, E, was measured by TMA with modulation of the tensile stress. Hence, it was possible to record the behavior of αe, αs and E during the structural changes by combining both modulations in a single measurement. A new technique was developed to calibrate the sample temperature. With this, accurate control of the modulated temperature of the specimen was achieved, independent of the changing heating rate.
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  • 7
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    ISSN: 0887-6266
    Keywords: temperature-modulated differential scanning calorimetry ; DSC ; heat capacity ; glass transition ; thermal relaxation ; polystyrene ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The glass transition can be measured at different experimental conditions. Using spectroscopic methods at relative high frequency the α-relaxation is measured in the thermodynamic equilibrium. In the caloric case we call this phenomenon thermal relaxation transition (TRT). With a conventional differential scanning calorimeter (DSC) the transition of the equilibrium (the melt) into a nonequilibrium (the glassy state) is measured. This effect is called thermal glass transition (TGT). In contrast to the TGT, the TRT can be described using the linear response approach. The temperature-modulated differential scanning calorimetry (TMDSC) technique superimposes a periodical temperature perturbation upon the constant scanning rate of conventional DSC. This technique combines a spectroscopic method with a linear temperature scan. Both the TGT and the TRT are measured simultaneous. Because the frequencies are relatively low in a TMDSC experiment, the temperature ranges of both transitions overlap. In this case, the experimental results show an influence of the TGT on the TRT. The reason of that is the deviation from the nonequilibrium. In this case, the fictive temperature is different from the external temperature. This effect can be described by means of a Tool-Narayanaswamy-Moynihan model for the TGT. Based on this model, a description of the complex heat capacity close to the thermal glass transition is shown. The influence of the beginning freezing-in process on the thermal relaxation is characterized by the fictive temperature. Using the presented description, a quantitative calculation of the nonlinear effects in the thermal relaxation is possible. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2165-2175, 1998
    Additional Material: 7 Ill.
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