RESUMO
In this work, polymethacrylates containing sulfonyl and nitrile functional groups were successfully prepared by conventional radical polymerization and reversible addition-fragmentation chain-transfer polymerization (RAFT). The thermal and dielectric properties were evaluated, for the first time, considering differences in their molecular weights and dispersity values. Variations of the aforementioned properties do not seem to substantially affect the polarized state of these materials, defined in terms of the parameters ε'r, ε"r and tan (δ). However, the earlier appearance of dissipative phenomena on the temperature scale for materials with lower molecular weights or broader molecular weight distributions, narrows the range of working temperatures in which they exhibit high dielectric constants along with low loss factors. Notwithstanding the above, as all polymers showed, at room temperature, ε'r values above 9 and loss factors below 0.02, presenting higher dielectric performance when compared to conventional polymer materials, they could be considered as good candidates for energy storage applications.
RESUMO
This work presents the synthesis of new poly(itaconate)s containing sulfone or nitrile pendant groups through conventional radical polymerization together with their characterization and comparison with poly(methacrylate)s containing identical groups. Structural and thermal characterization has been carried out in terms of Fourier transform infrared spectroscopy, differential scanning calorimetry, nuclear magnetic resonance, and thermogravimetric analysis. Characterized by broad band dielectric spectroscopy (BDS), all polymers showed dielectric constant values between 7 and 10 (at 25 °C and 1 kHz) and relative low dielectric loss values (≈0.02). BDS measurements showed, for all the polymers analyzed, notorious subglass transitions even at temperatures below -100 °C, resulting in a broad temperature interval in which these polymers exhibit high dielectric constant and could work without high losses. Therefore, these materials seem to be good candidates for dielectric applications such as energy storage, among others.
RESUMO
The characteristics of the electron-mirror effect (EME) image depend on both the scanning electron microscope parameters and the sample's physical properties. The behavior of human tooth (dentin and enamel) and synthetic hydroxyapatite samples submitted to the EME procedure is presented in this work. Polyethylene terephthalate (PET) and epoxy resin, two good EME producers, were used for comparison. A distorted EME image was observed in the obtained dentin's surface, but enamel and synthetic hydroxyapatite surfaces did not produce the EME. After ex situ calcination treatments of the teeth at 700 and 1,200°C, the EME was observed in dentin, enamel, and synthetic hydroxyapatite, but highly deformed EME images were produced. We show that these last observations are the result of the well-known charge-edge effect. After EME analysis, the calculated dielectric constant was 8.7 for dentin and 3.8 for PET. RESEARCH HIGHLIGHTS: Electron-mirror effect (EME) was observed in dentin but not in enamel or synthetic hydroxyapatite. Highly deformed EME images are produced in all samples after calcination at above 700°C. For dentin the calculated dielectric constant was 8.7 and for PET is was 3.8.