Temperature dependence of molecular dynamic arrangement in the vicinity of the glass transition of MEH-PPV: C60 based structures: X ray and impedance spectroscopy analysis

• Temperature dependence in term of structural arrangement of MEH-PPV: C60 is studied.
• The dielectrical behaviors of the composites are also studied.
• A dependence of these behaviors with the structural evolution is seen.
• The dielectrical properties are improved at 200 °C.

Dielectrical and electrical properties of the blend of poly[2-methoxy,5-(20-ethylhexyloxy)-1,4,-phenylene-vinylene] and fullerene molecules (C60) annealed at different temperatures, with indium tin oxide (ITO) and aluminum contacts. These structures were studied in the dark by means of impedance techniques analysis and current voltage characteristics. Structural evolution of the annealed films was studied by X-ray diffraction. The as cast film, exhibited three broad diffraction peaks at around 2Θ = 6°, 12° and 21.7° accompanied with two well defined diffraction peaks at wide angle at about 2Θ = 30.7° and 35.5°. The diffraction peaks at around 2Θ = 6° and 21.7 were attributed to MEH-PPV while the diffraction peaks at around 2Θ = 12°, 30.7° and 35.5° were originated from the effect of the incorporation of C60 molecules in the polymer matrix. As the temperature is increased to 125 °C, the intensities of the diffraction peaks at wide angles increase, indicating an increase in the crystallinity in the composite film and the peak at around 2Θ = 12° decreases progressively then at 125 °C it disappeared completely. When the temperature is increased further to 180 °C this peak reappears again and the diffraction peaks at 2Θ = 30.7° and 35.5° disappeared. These results suggested the occurrence of a crystalline transition in the composite film at about 125 °C. In addition, it reveals that the amorphous domain of the polymer was increased with annealing at elevated temperatures. The electrical and dielectrical behavior of MEH-PPV: C60 composites show a strong dependence with the structural evolution with thermal treatment.