Surface and mechanical properties of graphene–clay/polyimide composites and thin films

Nano-graphene sheets (NGS) and clay mixed fillers were dispersed in a high performance polyimide (PI) matrix by in situ condensation polymerization. The dispersive (γsd) and polar (γsp) surface energy components of NGS/PI, clay/PI and NGS–clay/PI composite films were studied by using dynamic contact angle analyzer with water and diiodomethane as wetting liquids. The total surface energy (γs) of NGS/PI composites increases with increasing NGS concentration while that of clay/PI composites decreases with increasing clay concentration. Addition of clay into NGS/PI composites decreases the surface energy of the resulting composites due to the presence of long chain organic modifiers and decreased external composite surface roughness. Investigating the influence of clay on the surface properties of graphene/polyimide composite provides a useful insight into a relatively cheaper surface modification methodology for graphene-based composite materials. The viscoelastic behavior of the NGS–clay/PI composites, investigated using dynamic mechanical spectrometry (DMS), showed significant improvement in storage modulus of the composite over that of the matrix (EC/EM ∼ 1835) at 4.5 vol.% clay concentration. Damping ability of the NGS–clay/PI composite, which is correlated with the area under the alpha (α) transition peak, was significantly improved in the presence of clay. X-ray diffraction showed the graphitic and clay diffraction peak at 26.5° and 4.76°, respectively.