Dielectric relaxation and thermal transitions in β-PVDF have been investigated by Thermo-Stimulated Current spectroscopy and
Differential Scanning Calorimetry respectively. A comparative study of spectra and thermograms has been performed.
The relaxation mode associated with the glass transition of the true amorphous phase is characterized by relaxation times
obeying a compensation law due to cooperative molecular movements. A conformationally disordered structure is proposed for
β-PVDF to explain thermal events occurring around 60°C. Ageing of ferroelectric properties of β-PVDF has been associated with
cooperative molecular movements liberated largely below the melting point.
Authors:A. Bernes, J. J. Martinez, D. Chatain, and C. Lacabanne
Relaxation phenomena in polycarbonate have been explored by Thermally Stimulated Current (TSC) spectroscopy. A comparative study of transitions by differential scanning calorimetry has also been undertaken. In the sub-Tg region, the observed relaxations have been associated with the diffusion of local defects along the chains. In the glass transition region, the annealing induces the segregation of two relaxation modes: the lower temperature component associated with the unstressed amorphous phase, the higher temperature component attributed to stressed amorphous phase responsible for the modules observed in electron microscopy and X-ray diffraction.
Authors:M. Mourgues-Martin, A. Bernes, and C. Lacabanne
Thermally Stimulated Current (TSC) spectroscopy and Differential Scanning calorimetry (DSC) have been applied to the characterization
of the microstructure of Poly (Ether Ether Ketone)/PEEK. the dielectric relaxation spectra show two modes, dependent upon
* for the mode stuated in the vicinity of the glass transition temperature, two components have been distinguished and attributed
to the molecular mobility in the ‘true amorphous phase’ and in the ‘rigid amorphous region’.
* below 0°C, two sub-modes appear, situated around-110°C and-75°C, due to the two different crystal entities, beads and laths.