Nano-graphene/polyimide composites with extremely high rubbery plateau modulus

Abstract

Nano-graphene sheets (NGS) were dispersed in a high performance polyimide (PI) matrix by in situ condensation polymerization. The viscoelastic behavior of PI and NGS/PI composite was investigated by using dynamic mechanical spectrometry (DMS) and extraordinary modulus enhancement was observed in the rubbery plateau region (>400°C) compared to the glassy region (<400°C). A modulus enhancement of 11,000%, 52,000% and 400,000% was obtained in the rubbery plateau region for NGS/PI composite at 1.18, 6.12 and 28.08vol.%, respectively, compared to a modulus enhancement of 100%, 108% and 500%, respectively, in the glassy region. The disparity in the modulus enhancement between the glassy region and the rubbery plateau region is due to the pronounced stiffening effect of hard fillers in a soft and flexible matrix such as rubber. Wide-angle X-ray diffraction (WAXD) was used to study dispersion of nano-graphene in the PI matrix, and graphene aggregates containing up to 46 single graphene sheets were obtained at about 0.29vol.%. WAXD pattern show the presence of graphitic peak at a diffraction angle of 26.5o. Raman spectroscopy show the presence of amorphous carbon (D band) and graphitic carbon (G band), at 1360 and 1537cm−1, respectively.