Glass transition of an epoxy resin induced by temperature, pressure and chemical conversion: a configurational entropy rationale

A comparative study is reported on the dynamics of a glass-forming epoxy resin when the glass transition is approached through different paths: cooling, compression, and polymerization. In particular, the influence of temperature, pressure and chemical conversion on the dynamics has been investigated by dielectric spectroscopy. Deep similarities are found in dynamic properties. A unified reading of our experimental results for the structural relaxation time is given in the framework of the Adam-Gibbs theory. The quantitative agreement with the experimental data is remarkable, joined with physical values of the fitting parameters. In particular, the fitting function of the isothermal tau(P) data gives a well reasonable prediction for the molar thermal expansion of the neat system, and the fitting function of the isobaric-isothermal tau(C) data under step- polymerization conforms to the prediction of diverging tau at complete conversion of the system.Comment: 16 pages, 8 figures, from the talk given at the 4th International Discussion Meeting on Relaxations in Complex Systems (IDMRCS), Hersonissos, Helaklion, Crete (Greece), 17-23 June 200

Polymer dynamics interpreted in terms of Adam-Gibbs theory

The investigation of dynamic properties of polymeric materials near the glass transition is one of the most important topics in the field of amorphous materials. Many theories were proposed in order to rationalise the dependence of dynamics on temperature, pressure and aging time. In this paper we briefly review recent works where the thermodynamic theory of Adam and Gibbs was successfully applied to reproduce dynamic properties in polymeric systems above and below the glass and discuss the main points of the debate in progress concerning the applicability of the theory

Trace elements in the atmospheric particulate of Milan and suburban areas. A study carried out by INAA

A preliminary part of a study initiated for monitoring the trace element levels in the atmosfere particulate of the city of Milan (north Italy) and of its suburban areas is presented. More than 25 elements were detd. along a period of 3 yr and in different weather conditions. The granulometric distribution of selected potentially toxic elements (such as V, Pb, Cd, Ni) was also detd. to evaluate their concns. in different inhalable fractions (alveolar and bronchial-tracheal). ree. Instrumental neutron activation anal. (INAA) was used for the determination of the great part of the elements while graphite furnace at. absorption spectroscopy (GF-AAS) was employed for the detn. of Pb and, in some cases, for Ni, Cd, and Cu

Evidences of a Common Scaling under Cooling and Compression for slow and fast relaxations: relevance of local modes for the glass transition

The present study demonstrates, by means of broadband dielectric measurements, that the primary α- and the secondary Johari-Goldstein (JG) β-processes are strongly correlated, in contrast with the widespread opinion of statistical independence of these processes. This occurs for different glass-forming systems, over a wide temperature and pressure range. In fact, we found that the ratio of the α- and β- relaxation times is invariant when calculated at different combinations of P and T that maintain either the primary or the JG relaxation times constant. The α-β interdependence is quantitatively confirmed by the clear dynamic scenario of two master curves (one for α-, one for β-relaxation) obtained when different isothermal and isobaric data are plotted together versus the reduced variable T g (P)/T, where T g is the glass transition temperature. Additionally, the α-β mutual dependence is confirmed by the overall superposition of spectra measured at different T-P combinations but with an invariant α-relaxation time

DC Electrical Transport in a New Conducting Polymer: Oxidized Poly(N-Vinylpyrrole)

D.c. electrical transport properties of pellets of oxidized poly(N-vinylpyrrole), a new conducting ladder polymer, are studied. D.c. conductivity data are coherent with a three-dimensional variable range hopping transport model. Relevant microscopic parameters of the model are inferred from data and are briefly discussed