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Alves, Natália M.; Mano, João F.; Ribelles, J.L. Gómez

doi:10.1023/a:1021609531577

Cited by 14 publications

(19 citation statements)

References 29 publications

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“…Assuming an Arrhenius form for (T), due to the short range of that are acceded (see data in Figure 7), the activation energy and the pre- T / ºC exponential factor may be calculated for each TS curve. More details on the calculation of thermokinetic parameters from TSR data may be found elsewhere [11]. It would be interesting to predict how TSR information could be compatible with usual DMA results, such as the one presented in section 3.1.…”

Section: Tsr Resultsmentioning

confidence: 82%

“…In all the experiments carried out in this work we used a heating rate of 4 K.min -1 and for the TS experiments T w =3 ºC. More details about these tests, including more experimental details can be found elsewhere [11,12].…”

Section: Techniquesmentioning

confidence: 99%

“…Similarly to Eq. (13) the fragility index may be calculated with m= h*/[ln (10)RT g ]. Different DSC traces obtained at 10ºC.min -1 , after different cooling rates are shown in Figure 10.…”

Section: Fragilitymentioning

confidence: 99%

“…TSR has been shown to be a very sensitive technique in polymer systems, including composites, semicrystalline polymers, inter-penetrated polymer networks and thermosets, especially if combined with DMA [8][9][10][11][12][13]. By means of the Thermal Sampling procedure (TS), the TSR technique also offers the possibility of experimentally decompose a complex process, characterised by a distribution of characteristic times, into its quasi-individual components.…”

Section: Introductionmentioning

confidence: 99%

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Departure from the Vogel behaviour in the glass transition—thermally stimulated recovery, creep and dynamic mechanical analysis studies

Alves

Mano

Ribelles

et al. 2004

Polymer

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Elsevier Alves, N.; Mano, J.; Gómez Ribelles, JL.; Gómez-Tejedor, JA. (2004). Departure from the Vogel behaviour in the glass transition -thermally stimulated recovery, creep and dynamic mechanical analysis studies. Polymer. 45(3): 1007-1017. doi:10.1016/j.polymer.2003.04.002. N.M. Alves et al. / Polymer 45 (2004 AbstractIn this work the study of the dynamics of the segmental motions close to T g of a poly(methyl methacrylate), PMMA, network was analysed by distinct mechanical spectroscopy techniques. Three techniques were employed: dynamic mechanical analysis (DMA), creep and thermally stimulated recovery (TSR). The timetemperature superposition principle was applied to the DMA and creep results, and master curves were successfully constructed. A change from a Vogel to an Arrhenius behaviour was observed in these results.Above T g it was found a distinct temperature dependence for the retardation times calculated from creep and the relaxation times calculated from DMA. This unexpected behaviour was attributed to the merging of the and the relaxations that occurs in PMMA systems. The activation energies (E a ) were also calculated from DMA, creep and TSR experiments. Above T g the E a values obtained agreed very well for all the techniques. In addition, the fragility exhibited by this material was investigated by the mechanical spectroscopy techniques referred above and by differential scanning calorimetry (DSC). The obtained values of the fragility index m indicated that the PMMA network is a kinetically fragile system. The thermodynamic manifestation of the fragility was also analysed.

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Section: Tsr Resultsmentioning

confidence: 82%

Section: Techniquesmentioning

confidence: 99%

Section: Fragilitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Departure from the Vogel behaviour in the glass transition—thermally stimulated recovery, creep and dynamic mechanical analysis studies

Alves

Mano

Ribelles

et al. 2004

Polymer

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“…This technique offers the interesting possibility of decomposing a complex process, characterised by a distribution of characteristic times, into narrow distributions of relaxations, by applying the thermal sampling procedure. It was shown that a commercial dynamic mechanical analyser can be used to perform TSR experiments [37,38].…”

Section: Some Years Ago a New Model Was Proposed By Gómez Ribelles Anmentioning

confidence: 99%

Molecular dynamics in polymeric systems

2004

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It is well known that the properties of polymeric materials depend strongly upon their chemical structure. Other more specific factors that may be related to the chemical structure also determine the macroscopic behaviour of such materials, namely the relative position of the different segments of the polymeric chain, the molecular architecture (molecular weight distribution, branching, copolymer organisation, cross-linking extent, etc.), the crystalline environment and the pressure/temperature conditions. All these factors have a common impact in the material: they are strongly correlated to the mobility on the molecular level. That is why a huge amount of work has been devoted to the study of translational/rotational mobility that occurs within the polymeric chains. This review is intended to provide a brief survey on such kinds of mobilities, how they can be studied and what are their main characteristics. Examples on systems studied in our groups will be provided, obtained by dielectric and mechanical spectroscopies and differential scanning calorimetry. It will be mainly focused on molecular motions that occur in the solid phase (i.e., to temperatures up to the rubbery plateau). The dynamics in blends or copolymers will be avoided here, as they would deserve a special discussion in their own context. Special attention will be paid to the glass transition and the mobility that occurs below and above it. The dynamics that are observed in peculiar systems, such as semi-crystalline or liquid crystalline polymers, will be addressed.

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Study of the Segmental Dynamics in Semi‐Crystalline Poly(lactic acid) using Mechanical Spectroscopies

Mano

2005

Macromolecular Bioscience

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The glass transition of poly(L-lactic acid) (PLLA) occurs not far above typical service temperatures (room or body temperatures) which has consequences on the material properties during its use, such as damping or the occurrence of structural relaxation. This work aims at characterising the glass transition dynamics of a semi-crystalline PLLA using both dynamic mechanical analysis (DMA) and thermally stimulated recovery (TSR). The main viscoelastic parameters have been characterised at 1 Hz using DMA and the master curve obtained after isothermal experiments at different temperatures provided a full picture of the solid-state rheological behaviour throughout a wide frequency range. The activation energies calculated from the shift factors agree with the TSR ones, exhibiting a maximum near the T(g). Above the T(g), the results can be described with the WLF model. In the glassy state, the activation energy decreases with decreasing temperatures being always higher than the prediction of the Adam and Gibbs theory, at least down to temperatures 30 degrees C below the T(g). This suggests the existence of non-arrested degrees of freedom in the glassy state, being consistent with the existence of a significant degree of cooperativity in the TSR results.

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Cited by 14 publications

References 29 publications

Departure from the Vogel behaviour in the glass transition—thermally stimulated recovery, creep and dynamic mechanical analysis studies

Departure from the Vogel behaviour in the glass transition—thermally stimulated recovery, creep and dynamic mechanical analysis studies

Molecular dynamics in polymeric systems

Study of the Segmental Dynamics in Semi‐Crystalline Poly(lactic acid) using Mechanical Spectroscopies

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