Etude d'une cellule coaxiale-cylindrique pour la caractérisation diélectrique large bande de matériaux à pertes

The full electromagnetic study of a short-ended pellet-cell coaxial-cylindrical discontinuity used for high-losses dielectric material characterization is presented in this article. The results obtained with this iterative method are plotted in abaque form.Nous présentons dans cet article l'étude électromagnétique complète de la discontinuité coaxiale-cylindrique d'une cellule pastille court-circuitée utilisée pour la caractérisation de matériaux diélectriques à pertes. Les résultats obtenus par cette méthode itérative sont présentés sous forme d'abaques

Dielectric properties of free-radical polymerizations: Molecularly symmetrical initiators during thermal decomposition

The first dedicated study investigating how the dielectric properties of free-radical initiators vary with both temperature and time is reported herein. The materials tested were chosen because they are standard initiators that are widely used by both industry and academia. Initially, each initiator was subjected to thermogravimetric analysis under the same temperature/time profiles, which reflects the mass lost from the materials when subjected to conventional heating. By comparing these data to the dielectric properties, we found that both the melting and decomposition points are directly related to large changes in the dielectric properties of the sample. We then used these data to investigate the likelihood of electromagnetic fields at microwave frequencies being capable of exerting an effect on the molecular decomposition of these initiating species, through a polarization−relaxation mechanism, and whether this effect could potentially alter the mechanistic pathways taken in free-radical polymerization chemistry. Finally, we considered whether direct molecular-based effects of electromagnetic fields at microwave frequencies on such initating species are responsible for the empirical observations related to polymerization that have been reported in the literature, such as rate and molecular-weight enhancements. Use Mobile Site Copyright © 2011 American Chemical Societ