A novel approach to the dielectric analysis of relaxation phenomena in glass-forming liquids is discussed. Instead of cooling, the system is polymerized so that the glass transition is approached by a chemical vitrification process. Measurements were carried out in a wide frequency interval covering 7 decades, from 10(3) to 10(10) Hz, on different polymerizing systems, namely two epoxy systems, the butyl acrylate and an unsaturated polyester. The relaxation function adopted for extracting the dielectric parameters is validated through a careful verification of the chemical and physical meaning of the changes observed in the dielectric susceptibility as the reaction gores on. The evolution of the shape of the relaxation function is discussed within the percolation theories developed for undercooled liquids and a satisfactory agreement between experimental results and theoretical predictions was found. The scaling behaviour vs. conversion of relaxation times of both main and secondary processes closely parallels those observed in many glass-formers vs. temperature and it can well be represented by Vogel Fulcher-like and Arrhenius-like equations, respectively.
Dielectric relaxation phenomena in polymers: Recent findings by chemical vitrification experiments
CAPACCIOLI, SIMONE;
1997-01-01
Abstract
A novel approach to the dielectric analysis of relaxation phenomena in glass-forming liquids is discussed. Instead of cooling, the system is polymerized so that the glass transition is approached by a chemical vitrification process. Measurements were carried out in a wide frequency interval covering 7 decades, from 10(3) to 10(10) Hz, on different polymerizing systems, namely two epoxy systems, the butyl acrylate and an unsaturated polyester. The relaxation function adopted for extracting the dielectric parameters is validated through a careful verification of the chemical and physical meaning of the changes observed in the dielectric susceptibility as the reaction gores on. The evolution of the shape of the relaxation function is discussed within the percolation theories developed for undercooled liquids and a satisfactory agreement between experimental results and theoretical predictions was found. The scaling behaviour vs. conversion of relaxation times of both main and secondary processes closely parallels those observed in many glass-formers vs. temperature and it can well be represented by Vogel Fulcher-like and Arrhenius-like equations, respectively.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
