Physico-chemical behaviour of irradiated polyimide thin films

The effect of Cu 3+ ion-beam irradiation on the microstructure of two polyimide ( PI ) films ( PMDA-ODA, Kapton ® and BTDA-ODA ) was examined using ATR-FTIR and XPS spectroscopy. The electrical conductivity, Mechanical and Electromechanical properties were also examined. It was found that Cu 3+ ion-beam irradiation was directly responsible for the disruption of the main chain imidic groups in the polymer, which indicated the breakdown of the backbone linkages of the polymer, via cleavage of the nitrogen of the imide and elimination of hydrogen from the PI molecular structure. Electrical conductivity characteristics of the PMDA-ODA films, revealed that they behaved as typical semiconductor films. The resistance of the irradiated films was found to be inversely proportional to temperature, confirming their semiconducting behaviour with calculated thermally sensitive activation barriers in the range 0.4–2.3 eV. The disruption of the main chain imidic groups in the polymer and the formation of the carbon rich channels affected both the tensile strength and the electromechanical properties of the PI films. This is evidenced by changes in Young’s Modulus, and they became slightly brittle at the highest levels of irradiation fluence. The electromechanical properties of PMDA-ODA irradiated films possessed GF values much higher those of conventional composites and an order of magnitude higher than any previously reported. Thus, the irradiated PI films are suitable as sensitive strain gauges with applications as strain sensors, provided they are protected from intense radiation sources