Leveraging trace nanofillers to engineer ultra-low wear polymer surfaces

Abstract

Trace nanofillers have proven unable to stabilize polymer surfaces due to their inability to reinforce the subsurface. Thus far, their effects on surface wear have been obscured by potentially unrelated subsurface mechanics. In this paper, we addressed this problem by first eliminating matrix (PTFE) subsurface instability with a secondary filler (5 wt% PEEK) and then by stabilizing the sliding surface using variable loadings of trace alumina nanofillers. At the optimal loading of 0.1 wt%, the nanofillers reduced wear rates of an already low wear PEEK-PTFE blend by an unprecedented 50-fold. The minimum loading of 0.01 wt% reduced wear by 10-fold. Surface analysis revealed that trace nanofillers triggered ultra-low wear by catalyzing tribochemical changes that effectively crosslinked, anchored, and stabilized near-surface polymer chains. The degradation of wear performance at nanofiller loadings well above the 0.1 wt% optimum suggested that the mechanical detriments of greater loadings outweighed their tribochemical benefits. To our knowledge, this study is the first to isolate the effects of trace nanofillers on polymer surface stability and the first to demonstrate their radical wear-reducing potential. This hybrid approach – independently targeting surface and subsurface stability – serves as a roadmap for isolating the effects of other important nanofillers (e.g. CNT's) and engineering ultra-stable tribological surfaces.