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Nanoplastic particles (NPs) are ubiquitously present in the environment and their potentially harmful effects on ecological systems remain largely unknown. Owing to their minute spatial dimensions, both the identification and characterization of NPs represent major challenges. In this work, two scanning probe microscopy-based procedures are established. Conventional atomic force microscopy (AFM) is applied with commercially available pyramidal tips to assess the surface topography as well as the nanoscale deformation and adhesion of individual intentionally synthesized NPs. In addition, these NPs are fastened to the modified tip apex of AFM cantilevers via advanced nanomanipulation to form colloidal probes, allowing the adhesion and friction behavior of entire NPs to be studied on well-defined substrates with unprecedented resolution. In this way, the nanoscale properties of an NP can be correlated with its particle-scale adhesion and friction behavior. This methodology thus promises to gain new insight into the complex surface-related interactions of NPs and can be applied to the study of NPs originating from the breakdown of plastic debris within the environment.

Despite considerable research efforts, the influence of contact line tension during wetting at the nanoscale and its experimental determination remain challenging tasks. So far, molecular dynamics simulations and atomic force microscope measurements have contributed to the understanding of these phenomena. However, a direct measurement of the size dependence of the contact angle and the magnitude of the apparent line tension has not been realized so far. Here, we show that the contact angle is indeed dependent on the drop size for small drop diameters and determine the magnitude of the apparent line tension via liquid-metal based measurements of advancing and receding contact angle inside a scanning electron microscope. For this purpose, a robotic setup inside an electron microscope chamber and oxide-free Galinstan droplets—produced via an electromigration-based and focused ion beam irradiation-assisted process—are employed. Using the first-order correction of Young’s equation, we find an apparent line tension value of 4.02 × 10−7 J/m for Galinstan© on stainless steel.

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