Abstract
<jats:p>Swelling is expected to be an inherent property of nanoplastics, defining their interactions with their environment. First, we created models for polyurethane (PUR) and polyethylene terephthalate (PET) nanoplastics, which, based on structural descriptors, including density, these particles were found to exhibit realistic geometries. Using these models, we identified the sequence of steps that result in the swelling of these nanoplastics in water, trifluoroacetic acid, and dimethylformamide. For PET, bearing weaker polymer-polymer interactions, swelling was found to be a continuous process. In the case of PUR, in which hydrogen bonding forms a dominant type of intermolecular interactions within the polymer, these hydrogen bonds first have to be broken by the solvent, thereafter, solvent molecules penetrating the particle can cleave off individual chains in separate steps, resulting in a more complex swelling mechanism. The resulting mechanistic picture is consistent with earlier models of polymer swelling deduced from second order kinetics.</jats:p>