Nanoscale adhesion and friction behavior of individual nanoplastic particles under varying environmental conditions

Nanoplastic particles (NPs) having dimensions below 1000 nm are ubiquitously present in the environment. The detection, characterization, and understanding their interaction with other surfaces, including human organs, has become a challenge due to their minute size. In this paper, an advanced technique namely colloidal probe atomic force microscopy (CP-AFM), fabricated by robotic nanomanipulation inside the scanning electron microscopy (SEM) chamber by attaching an individual NP at the end of the modified tip apex of an AFM cantilever, is employed to investigate the adhesion and friction of commercially available individual NPs as well as mechanically degraded NPs with different substrates. Measurements are conducted on three individual smooth and flat substrates: silicon oxide (SiO₂), mica, and highly ordered pyrolytic graphite (HOPG) in ambient atmosphere, aqueous medium, and dry nitrogen environment. We have observed significant variations in adhesion and friction for all test substrates under different environmental conditions. Friction measurements on different test substrates for individual NPs indicate that friction is highly dependent on the type of substrate. Additionally, the mechanically degraded NPs show slight modification of adhesion and friction as compared to the primary NPs, indicating the effect of degradation. The present methodology thus enables a detailed insight into nanoscale NP–surface interactions and can be applied for the study of NPs from the environment, such as seawater.