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排序方式: 共有66条查询结果,搜索用时 15 毫秒
41.
Zumailan A. Denis G. Dargent E. Saiter J. M. Grenet J. 《Journal of Thermal Analysis and Calorimetry》2002,68(1):5-13
PET films uniaxially drawn in hot water are studied by means of conventional DSC and modulated DSC (MDSC).Glass transition
is studied by MDSC which allows to access the glass transition temperature T
g and the variations of ΔC
p=C
p1−C
pg (difference between thermal capacity in the liquid-like and glassy states at T=T
g). Variations of T
g with the water content (which act as plasticizer) and with the drawing (which rigidifies the amorphous phase) are discussed
with regard to the structure engaged in these materials. The increments of ΔC
p at T
g are also interpreted using a three phases model and the 'strong-fragile’ glass former liquid concept. We show that the ‘fragility’
of the medium increases due to the conjugated effects of deformation and water sorption as soon as a strain induced crystalline
phase is obtained. Then, ‘fragility’ decreases drastically with the occurring rigid amorphous phase.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
42.
M. E. Godard F. Burel J. M. Saiter J. Grenet 《Journal of Thermal Analysis and Calorimetry》1998,51(3):897-903
This work presents new results concerning characterization of polymethyl(α-n-pentyl)acrylate polymer by means of thermal analysis. In differential scanning calorimetry investigations, the measured values of T g, T f and ΔC p, i.e. the glass transition temperature, the fictive temperature and the heat capacity step at T g, show that the polymer can be considered as fragile. Thermogravimetric analysis revealed two mass losses, the first, at low temperature, being associated with the evaporation of water molecules, and the second, at high temperature, corresponding degradation of the polymer. This degradation is a two-step phenomenon. Finally, study of the β and the α transitions by elementary and complex TSDC led to the following values: T β=?40°C, T α=36°C, T c=47°C, τc=2.5 s and ΔH=85 to 165 kJ mol?1. 相似文献
43.
44.
This work compares the equilibrium states reached by glassy selenium (g-Se) after several ageing durations at temperatures lower than the glass transition temperature T g, with the forecasts given by the configurational entropic model. The comparison is carried out through experimental data collected both on glassy samples after short-term ageing and on glassy samples older than 20?years, kept at room temperature. It is shown that the configurational entropic model is not able to describe the behaviour of g-Se, both at short- and long-ageing terms with the same set of fitting parameters. For short-term ageing, the forecasts given by the entropic model are in good agreement with the experimental data; the hypothesis that the heat capacities corresponding to the equilibrium state and to the state extrapolated from the liquid differ by an amount δ is therefore properly justified. For long-term ageing, the amount δ vanishes and the assumption does not hold any longer. Indeed, experimental results support the idea that at least two separate mechanisms of relaxation coexist in the physical ageing of g-Se, one with very fast kinetics and the other with much slower kinetics. 相似文献
45.
Ledru J. Saiter J. M. Grenet J. Youssef B. Burel F. Bunel C. 《Journal of Thermal Analysis and Calorimetry》1999,58(1):13-18
Polyurethane acrylate resins cured by two different ways, a thermal way and a photochemical way, are investigated by means of differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC). Even if both curing methods lead to the same material from a chemical point of view, we show that important differences exist between the thermocured resin and the photocured resin in terms of molecular relaxation behaviour.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
46.
N. Delpouve A. VuillequezA. Saiter B. YoussefJ.M. Saiter 《Physica B: Condensed Matter》2012,407(17):3561-3565
Molecular dynamics at the glass transition of three lactose/oil glassy systems have been investigated according to the cooperativity and fragility approaches. From Donth's approach, the cooperativity length is estimated by modulated temperature calorimetric measurements. Results reveal that modification of the disaccharide by oil leads to increase the disorder degree in the lactose, the size of the cooperative domains and the fragility index. These particular hydrogen-bonded organic glasses follow the general tendency observed on organic and inorganic polymers: the higher the cooperativity length, the higher the value of the fragility index at Tg. 相似文献
47.
J. M. Saiter N. Delahaye A. Bardat E. Chatenet 《Journal of Thermal Analysis and Calorimetry》1998,51(3):905-911
Different aqueous solutions of sucrose-NaCl-protein with different sucrose/NaCl contents were investigated by DSC and OTA (optical thermal analysis). The crystallization, melting and also the kinetics of freeze drying were analyzed. The first results show that coupling these analyzes might lead to a better understanding of the events which occur during the phase changes. In particular the kinetics of freeze drying were found to be drastically different for systems with different compositions. 相似文献
48.
Two types of bacterial semi-crystalline copolyesters, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB) are studied neat or with 8 wt% of Cloisite® C30B (C30B) organoclays. Wide Angle X-ray Diffraction (WAXD) and Differential Scanning Calorimetry (DSC) reveal that the nanoclays are partially intercalated, exfoliated and agglomerated. With selected sample preparation, the crystalline phase is unaffected by the C30B presence. Broadband Dielectric Spectroscopy (BDS) measurements showed no influence of the nanoclays on the secondary local relaxations modes of both polymers and on the segmental relaxation of P3HB4HB. Nevertheless, a strong modification of the α relaxation of PHBV has been observed after incorporation of C30B. A strong decrease of the fragility index and of the glass transition temperature revealed an increase of the molecular mobility in the amorphous fraction influenced by the nanoclays. 相似文献
49.
Steven Araujo Florian Batteux Wenlong Li Lena Butterfield Nicolas Delpouve Antonella Esposito Li Tan Jean-Marc Saiter Mehrdad Negahban 《Journal of polymer science. Part A, Polymer chemistry》2018,56(20):1393-1403
Kinetic fragility and cooperativity length, two major characteristics of the relaxation dynamics at the glass transition, are, respectively, investigated by dynamic mechanical analysis and modulated temperature differential scanning calorimetry in a series of interpenetrated polymer networks based on acrylate and epoxy systems. The relaxation dynamics are impacted by two variables: the rigidity of the network, and the structural heterogeneity resulting from blending. However, the fragility and the cooperativity do not vary similarly. The glass transition progressively broadens as the mass fractions of acrylate and epoxy become equivalent, leading to a strong decrease in cooperativity. On the other hand, under the same conditions, the fragility transitions between the lower value of pure acrylate and the higher value of pure epoxy. This divergence helps concluding that the variations in the temperature dependence of the relaxation time are not purely related to the more or less cooperative nature of the glass transition. By splitting the fragility index in a volume contribution and an energetic contribution, it is shown that the contribution of cooperativity to the variations of the relaxation time with temperature is increased under two structural conditions: low backbone rigidity and high intermolecular interactions. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1393–1403 相似文献
50.
Caroline Terrié Larisa Dobircau Preetha Gopalakrishnan Antoine Galandon Redouan Saiah Richard Gattin Nathalie Leblanc Jean Marc Saiter 《Macromolecular Symposia》2010,290(1):132-136
Summary: A new biodegradable thermoplastic material based on a wheat flour by-product has been developed. The influence of various additives (glycerol, silica) and fibers (flax, cotton, hemp) on the mechanical properties of the material has been investigated. The development of expanded materials is also presented. 相似文献