Time Temperature Superposition principle and cooperativity in ion irradiated poly (ether ether ketone)

dependent dielectric relaxation spectra of ion irradiated (11.2 MeV H+ and 25.6 MeV He2+) poly(ether ether ketone), (PEEK) were measured at frequencies between 50 and 105 Hz. Changes in the intensity of the β relaxation of PEEK with ion irradiation are mainly related with oxidation, but cross linking does not have a marked effect on the mobility of small localized groups in this region. In contrast the α transition is extremely sensitive to the presence of cross links and the glass transition temperature increases progressively with absorbed dose. The data were analyzed by Cole-Cole, Cole-Davidson, Havriliak-Negami and Kohlrausch-Williams- Watts equations. The results showed that the Cole-Cole, Havriliak-Negami and the Kohlrausch-Williams-Watts formalisms could well describe the dielectric spectrum for both amorphous and irradiated PEEK in the frequency and temperature range studied. With the KWW function, it was possible to describe the results in light of the coupling model. The observed decrease in the KWW β parameter resulted from the increase of inter-chain coupling between the relaxing units caused by the growing hindrance with increasing degree of cross linking. The results of HN analysis were explained in term of the scaling model and indicated that the local motions in amorphous PEEK were unaffected by irradiation, but a slowing down of the longrange molecular motions was taking place with increasing cross linking density of the polymer. The TTS were carried out by mean of the Williams–Landel–Ferry (WLF) equation from which the material properties of ion irradiated PEEK were estimated. Crosslinking not only elevates g T but also increases the dynamic fragility of PEEK chains around the g T . The average size of a cooperative rearranging region (CRR) was observed to increase with cross linking and this was accompanied with an increase in the apparent activation energy of the relaxation process. Although the general irradiation effects are similar for both ion, but there were some indications that the dielectric properties of polymers are influenced by the LET effect of the irradiated ion used. The validity of high efficiency 2D COS-DRS techniques to study the dielectric relaxation processes in amorphous and ion irradiated PEEK in the temperature domain was demonstrated. It was possible to locate the position of the water motions in the dielectric spectrum of PEEK. On irradiation, a new relaxation is appeared in the lower temperature side of the β -relaxation which is assigned to main-chain phenyl motions of the cross linked units of the polymer. On the other hand, introducing polar groups to the structure of PEEK enables more water/moisture to be absorbed and as a result increasing the intensity of the β -relaxation. The analysis in the region of glass relaxation showed that there are three processes that changing in different directions with respect to ion irradiation dose. These are at 160 °C, 175 °C and 240 °C. Hybrid 2d correlation was used to investigate the effect of the so called LET effect and the results showed that helium ions are more effective in cross linking PEEK (author).