Effect of Nanodiamond (ND) Surface Functionalization on the Properties of ND/PEEK Composites

This paper explores the effect of nanodiamond (ND) surface chemistry on the structure and properties of composites of ND melt-blended with poly(ether-ether-ketone) (PEEK). ND functionalized with phenylphosphonate (PPA) resulted in ND/PEEK composites with improved filler dispersion based on visual observations and surface topography measurements. As-received oxidized ND (OND) reduces PEEK's lamellar spacing and degree of crystallinity, as does PPA-modified carboxylated ND, which has low PPA graft density. PPA-modified OND does not significantly alter PEEK's crystalline structure or degree of crystallinity. Sonication during PPA grafting on OND increases composite thermal conductivity by up to 38% relative to pure PEEK. ND/PEEK composites have dielectric permittivity values comparable to and in some cases lower than pure PEEK and electrical conductivity values no greater than pure PEEK. The combination of enhanced thermal conductivity, low dielectric permittivity, and low electrical conductivity makes ND/PEEK composites attractive for high-temperature electronic device applications.