Polymer Lab., Polymer Research Group, Physics Department, Faculty of Science, Mansoura University, 35516, Mansoura, Egypt.
We report in this work the results of dielectric studies on blends of PVVH and PMMA. The dielectric techniques used was thermally stimulated depolarization currents (TSDC) in the temperature range from 300 to 420 K, in the vicinity of the glass transition temperature. Global spectra of both PVVH and PMMA are characterized by two relaxation peaks, a- and ρ-relaxation. The α-relaxation is associated with the main glass transition of the material and ρ-peak which is attributable to space charge. On blending the spectra showed two peaks corresponding to a-relaxation of both PVVH and PMMA. The position of the peak temperature Tm (a-relaxation of PVVH) is shifted toward the higher temperature side as PVVH constituent decrease. The disappearance of the ρ-peak, accompanied by the displacement of the α-peak to higher temperature, is the result of the higher thermal stability of the permanent dipoles, which is strongly influenced by the blending. The global TSDC spectrum of 50/50 wt% with varying poling field revealed the samples are characterized by two distinguished relaxation peaks. The first one has been observed in the temperature range from 348K to 361 K, whereas, the second one has been detected at a higher temperature, T=375 K. Thermal sampling (TS) technique was used to get more information about the fine structure of samples. The kinetic parameter such as activation energy, pre-exponential factor and dipole-dipole interaction strength parameter was determined by using iterative technique depending on Arrhenius relaxation model. In both blended samples, the continuous distribution of pre-exponential factors over activation energies observed might correspond to a single relaxation mode. Linearity was found to exist between the activation energy and the logarithm of the pre-exponential factor of the α-relaxation confirming the validity of the compensation laws.
TSDC, glass transition, molecular relaxation, relaxation time, activation energy, compensation
