A B S T RA C T:From measurements of dielectric losses as a function of frequency and temperature, as well as thermally stimulated depolarization currents, performed on a dry Na-montmorillonite, a qualitative description of the conduction mechanism has been proposed for this type of material. A representative approach related to the polarization phenomenon determined on this material led to the evaluation of the elementary energy Wj, connected with the reorientation of the dipoles during the hopping process. The results show the coherence between the polarization conductivity and the thermally stimulated currents methods.

Charging and discharging currents flowing through polyethylene terephthalate (PET) ultrathin films (1.5–12 μm) were measured by the use of a two-electrode configuration involving opposite lateral contacts. A study of the influence of electrification time, applied electric field, film thickness, nature of electrodes, and water content was carried out on both transient and steady-state conduction. The transient behavior can be interpreted in terms of dipolar orientation and relaxation processes while steady-state conductivity can be mainly accounted for in terms of Schottky emission. A comparison between PET and polyethylene naphthalate films is also reported.

Dielectric losses measured on a zeolite sample have been investigated to correlate these measurements with surface thermodynamic. The polarization conductivity measurement allows the determination of variables which are linked to the adsorption enthalpies and entropies but also to the system dynamic. To quantitatively interpret the results, it is necessary to know the energetic heterogeneity of the solid sample. The thermally stimulated current measurement (TSDC) appears as a possible tool. Therefore this new method of studying adsorption by combining two techniques seems promising. This paper is an introduction to the work under development.

No abstract

The microtacticity of polymethacrylates prepared by radical initiated polymerization of monomers with side groups of increasing bulkiness is determined by high resolution nuclear magnetic resonance of the corresponding poly(methy1 methacrylates).The syndiotacticity decreases systematically from poty(methy1 methacrylate) to poly-(triethylrnethyl methacrylate) in the series of the saturated polymers.The aromatic polymethacrylates have a lower syndiotacticity than the corresponding saturated polymers and poly(trity1 methacrylate) is the extreme case.The microtacticity of the polymers is undoubtedly determined by the bulkiness and the polarisability of the ester group as well as by specific interaction between the aromatic rings. ZUSAMMENFASSUNG:Die Mikrotaktizitiit von radikalisch polymerisierten Polymethacrylaten, die in der Seitenkette des Monomeren immer grol3ere Gruppen haben, wird durch die hochaufgelosten Kernresonanzspektren der entsprechenden Polymethylmethacrylate bestimmt.Die Syndiotaktizitiit vermindert sich schrittweise von Polymethylmethacrylat bis zu Polytriathylmethylmethacrylat in der Reihe der gesattigten Polymeren. Die aromatischen Polymethacrylate haben eine geringere Syndiotaktizitat als die entsprechenden gesattigten Polymeren. Polytritylmethacrylat stellt den Extremfall dar.Die Mikrotaktizitiit der Polymeren folgt sowohl aus der GroDe und der Polarisierbarkeit der Estergruppe als auch aus der Wirkung, die die aromatischen Ringe aufeinander ausuben.