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In this work, the molecular mobility at the glass transition of poly(vinyl acetate) (PVAc) and poly(ethylene-co-vinyl acetate) (EVA) amorphous sample series was investigated. The temperature and pressure dependences of the intermolecular interactions were studied from time–temperature–pressure superpositions and from the relaxation time dispersion of the segmental relaxation. The difference in terms of intermolecular interactions due to the lateral group ratio of vinyl acetate (VAc) was then estimated from the activation volume and related to the cooperative behavior. The isobaric fragility and its two contributions (thermal and volumetric) were estimated through high pressure broadband dielectric spectroscopy measurements. The volumetric and thermal contributions show different behaviors as a function of the VAc ratio and as a function of the pressure. Thus, the study of the PVAc/EVA series has allowed us to emphasize that the intramolecular and intermolecular interactions induced by the dipolar pendant groups directly influence the thermal and volumetric contributions to the isobaric fragility. [ABSTRACT FROM AUTHOR]

The blurring around the link between the isobaric fragility and the characteristic size of cooperative rearranging region for glass-forming liquids has been cleared up by considering volumetric and thermal contributions of the structural relaxation. The measurement of these contributions is carried out for three amorphous thermoplastic polymers using broadband dielectric spectroscopy under pressure, providing an understanding of the link between isobaric fragilities, glass transition temperatures, and microstructures. The cooperative rearranging region (CRR) volume is calculated as a function of pressure using the extended Donth's approach, and the values are compared with the activation volume at the glass transition under different isobaric conditions. By combining these different results, a link between the chemical structure and the influence of pressure/temperature on the molecular mobility can be established. Furthermore, this study shows also a strong correlation between the activation volume, leading to the volumetric contribution of the isobaric fragility, and the CRR volume. Finally, this work highlights the influence of inter- and intra-molecular interactions on thermal and volumetric contributions of the isobaric fragility as a function of pressure. [ABSTRACT FROM AUTHOR]

Controlling the cooling rate experienced by a material during a manufacturing process is a challenge and a major issue. Industrial processing techniques are very diverse and may involve a whole range of cooling rates, which are sometimes extremely high for small and/or thin manufactured parts. For polymers, the cooling rate has consequences on both the microstructure and the time-dependent properties. The common cooling rates associated with conventional calorimetric measurements are generally limited to a few tens of degrees per minute. This work combines several calorimetric techniques (DSC, modulated-temperature DSC, stochastically-modulated DSC and Fast Scanning Calorimetry) to estimate the critical cooling rate required to melt-quench fast-crystallizing polyesters to their fully amorphous state, based on the example of a series of poly(alkylene trans-1,4-cyclohexanedicarboxylate) (PCHs) with a number of methylene groups in the main structure of the repeating unit n C H 2 varying from 3 to 6. The even-numbered ones require faster cooling rates (about 3000 K s−1 for n C H 2 = 4, between 500 and 1000 K s−1 for n C H 2 = 6) compared to the odd-numbered ones (between 50 K min−1 and 100 K s−1 for n C H 2 = 3, between 10 and 30 K min−1 for n C H 2 = 5). [ABSTRACT FROM AUTHOR]

We present an experimental and theoretical exploration of well‐dispersed, distinctively stable, fumed SiO2 crosslinked polyethylene (XLPE) nanocomposites. The mechanical properties of fumed SiO2 /XLPE nanocomposites were assessed with different concentrations of fumed SiO2, which had noticed that network morphology was immensely influential for the performance of mechanical properties. A reasonable exploration of micromechanical models of composites indicated that the theories of Nicolais–Narkis, and Pukanszky provided an excellent fit to yield strength data of the composites considering the effect of the interphase between XLPE and SiO2. Furthermore, it highlights that the experimental data can be superimposed with the static micromechanical models of Nicolais–Narkis, and Pukanszky. Owing to the proper dispersion of the SiO2 nanospheres in the XLPE matrix, the filler‐polymer interactions are found to be enhanced. Moreover, it resulted in the excellent insulation properties of the nanocomposites, which makes it a better candidate for electrical cable insulating materials. The combined results of structural characterizations by Fourier Transform Infrared Spectroscopy (FTIR), X‐Ray Diffraction (XRD), Differential Scanning Calorimeter (DSC), Dynamic Mechanical Analysis (DMA), Atomic Force, and Transmission Electron Microscopy (AFM, TEM) confirmed the role of fumed SiO2 as a reinforcing mediator in the current system. [ABSTRACT FROM AUTHOR]

The study of molecular level interactions in elastomer composites has got very scant attention even though a large number of studies are going on in this topic. This work embodies the understanding of confinement effects in natural rubber (NR)/ ZnO composites from micro to nano length scales, and their influence on macroscopic properties of the composites. The interactions between fillers and matrix are characterized from the Donth's approach, which allows estimating the cooperativity size Nα at the glass transition, Nα being directly related to the filler‐matrix interactions. The improved properties of NR‐nano ZnO composites can be attributed to microstructural and morphological changes due to nano ZnO in the NR matrix. A correlation between Nα, the constrained volume Cv and the thickness of immobilized polymer chains χm at the glass transition has also been established. Thus, this work proves that the Donth's approach is a powerful probe to estimate the enhance of mechanical properties in nanocomposites from calorimetric investigations. [ABSTRACT FROM AUTHOR]