Effect of the Surface Hydrophobicity–Morphology–Functionality of Nanoplastics on Their Homoaggregation in Seawater

The way nanoplastics aggregate in the environment is one of the key properties that control their final fate and impact on the environment. In the present work, to better predict their transportation pathways, nanoplastic homoaggregation was studied in saltwater to predict the behavior in seawater. We designed nanoplastic models that are free of additives with a chemical control of the surface to model surface weathering. The samples present a wide distribution of relevant surface properties such as functionality (ionizable carboxylic group, 0.10 to 1.7 mmol g–1), hydrophobicity (surface energy, 2.20 to 37.5 mJ m–2), surface morphology (smooth or “raspberry-textured),” zeta potential (−31 to −21 mV), and anisotropy in shape. The critical coagulation concentration (CCC) measurements demonstrate that spherical nanoparticles are more stable in seawater (CCC > 600 mmol L–1) than anisotropic nanoplastics (CCC ∼ 100 mmol L–1). The results highlight the importance of considering the surface properties and shape when assessing the behavior of nanoplastics in the environment.