Nucleation and detachment of polystyrene nanoparticles from plowing-induced surface wrinkling

We report the formation of spherical particles (up to 250 nm in diameter) from polystyrene surfaces repeatedly scratched by atomic force microscopy nanotips (nominal radius < 10 nm) along a series of parallel lines. The particles nucleate from the crests of the ripple profiles formed in the beginning of the scratch process. They are subsequently detached and progressively displaced by the tip across the ripples till the edge of the scanned area, where they pile up without coalescing. The detachment occurs smoothly without static friction peaks, suggesting that the particles are torn off as a result of a crazing mechanism induced by the tip when it is pushed against the ripple crests. Considering the negative impact of nanoplastics on the environment and human health, and the absence of established methodologies for a quantitative analysis of these processes at the level of single particles, our results will help to promote systematic characterization of plowing wear on different polymeric materials and different environmental conditions.