Fabrication and macro/nanoscale characterization of aggregated and highly de-aggregated nanodiamond/polyacrylonitrile composite thick films

Nanodiamond/polyacrylonitrile (PAN) thick-film composites containing aggregated ultra-dispersed (UDD) and highly de-aggregated nanodiamond (ND) fillers are fabricated using bead-milling and solution-casting methods at additive loadings up to 30 wt%. Films containing oxidized nanodiamond fillers (ox-UDD and ox-ND) having potentially high surface reactivity or decarboxylated fillers (deox-UDD and deox-ND) having reduced surface reactivity have been characterized by FT-IR, TGA, DSC, TEM, EDS elemental analysis, nanoindentation, and tensile testing. While both nanoindentation and tensile testing measurements confirm enhancement in elastic modulus (E) for ox-UDD/PAN and ox-ND/PAN thick films compared to pure PAN films, the relative trend in these enhancements differs according to testing method (Eox-UDD/PAN > Eox-ND/PAN by nanoindentation; Eox-ND/PAN > Eox-UDD/PAN by tensile testing). Tensile strength and strain-to-failure measurements indicate superior property enhancements for highly de-aggregated ox-ND/PAN thick films. At 30 wt% filler loading, ox-ND/PAN elastic modulus increases by nearly 80% and tensile strength increases by nearly 60% relative to pure PAN films. At low ox-ND filler loadings, significant enhancements in mechanical properties are realized without incurring losses in film ductility.