1,720,971 research outputs found
Hybrid Nanofillers for Polymer ReinforcementSynthesis, Assembly, Characterization, and Applications
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Hybrid Nanofillers for Polymer ReinforcementSynthesis, Assembly, Characterization, and Applications
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Study of PVAc/EVA polymer series: Influence of the inter-/intra-molecular interaction ratio on the molecular mobility at the glass transition
No full textInternational audienceIn 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
Highlighting the interdependence between volumetric contribution of fragility and cooperativity for polymeric segmental relaxation
No full textInternational audienceThe 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
Distinct dynamics of structural relaxation in the amorphous phase of poly(l-lactic acid) revealed by quiescent crystallization
No full textFast scanning calorimetry (FSC) experiments were performed to investigate physical aging in amorphous and semi-crystalline poly(L-lactic acid)s (PLLAs) that were thermally crystallized under conditions leading to the α′- or α-crystalline form, and either favouring or inhibiting the development of a rigid amorphous fraction (RAF). The enthalpy of recovery was calculated after two procedures of rescaling to the content of the whole amorphous phase and also to the only content of the mobile amorphous fraction (MAF), which helped in clarifying the contribution of the RAF. From the dependence of the structural relaxation rate on the aging temperature, two regimes were evidenced for all samples. In the aging temperature domain situated close to the glass transition, the structural relaxation occurs significantly faster in the MAF. Its rate is independent of the aging temperature and is not influenced by the microstructure. However, the distance to equilibrium is higher in samples for which the coupling is strong between crystal and amorphous, implying that the time to reach equilibrium is also higher. In contrast, at low aging temperatures, for which the whole amorphous phase can be considered as solid, MAF and RAF exhibit the same structrural relaxation rate. This convergence in the relaxation kinetics by decreasing the temperature of physical aging was interpreted as the evolution of relaxation dynamics in the MAF from segmental to local. This change is highlighted by the comparison between MAF and RAF relaxation kinetics, but it occurs similarly in a pure amorphous system.Peer reviewe
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Influence of strain rate and Sn in solid solution on the grain refinement and crystalline defect density in severely deformed Cu
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