Surface modification of nanodiamond and its incorporation in nanodiamond/peek nanocomposites.

摘要

The continued miniaturization of electronic device components requires new lightweight polymers with high thermal stability, high thermal conductivity, low electrical conductivity, and low dielectric constant. Composites of nanodiamond (ND) and poly-ether-ether-ketone (PEEK) are candidates for these applications due their unique combination of properties. The objectives of this research are to explore new routes for surface functionalization of nanodiamond (ND), develop methods for maximizing dispersion of ND as a nano-scale filler in PEEK, and characterize the effect of dispersed ND on the mechanical, thermal and dielectric properties of ND/PEEK composites. Initial attempts to disperse different kinds of commercially available, as-received ND in PEEK were yielded low quality composites due to ND agglomeration and low thermal stability. Thus we began to explore chemical grafting of phenylphosphonate (PPA) onto oxidized ND (OND) and carboxylated ND (CND), hypothesizing that the phenyl functional group would render the NDs more compatible with aromatic PEEK. Detailed characterization results, including 31P NMR, FTIR, and XPS, indicate successful grafting, resulting in arylation of ND, increased ND thermal stability, and better compatibility with organic solvents. Sonication during the grafting promotes more complete exposure of the ND surface to PPA grafting, resulting in even better ND dispersion in organic solvents. PPA-modified OND and CND were then melt-blended with PEEK to produce ND/PEEK composites. Surface tomography results suggest that all PPA-modified NDs were adequately dispersed in PEEK, with OND showing better dispersion due to its higher PPA graft density. The presence of PPA-modified ND has minor impact on PEEK crystallinity based on XRD and DSC data. Tensile testing and DMA results suggest that ND/PEEK composites generally retain the mechanical properties of PEEK with some sacrifice of ductility. TGA data indicate that all ND/PEEK composites have excellent thermal stability at temperatures up to 400°C as needed for PEEK melt processing. ND/PEEK composites had dielectric constants lower than or comparable to that of pure PEEK, with low dielectric losses in most cases. Addition of OND or CND to PEEK generally increases the thermal conductivity relative to pure PEEK; the increase reached 38% for PPA-modified OND (prepared with sonication) blended with PEEK. These results suggest that ND/PEEK nanocomposites are good candidates for use in electronic device applications.