Repulsive interactions of eco-corona covered microplastic particles quantitatively follow modelling of polymer brushes

Environmental fate and toxicity of microplastic particles is dominated by their surface properties. In the environment an adsorbed layer of biomolecules and natural organic matter forms the so-called eco-corona. A quantitative description of how this eco-corona changes the particles' colloidal interactions is still missing. Here, we demonstrate with colloidal probe-atomic force microscopy that the formation of the eco-corona on microplastic particles introduces a soft film on the surface which changes the mechanical behaviour. We measure single particle-particle interactions and find a pronounced increase of long-range repulsive interactions upon eco-corona formation. These force-distance characteristics follow well the polymer brush model by Alexander and de Gennes. We further compare the obtained fitting parameters to known systems like polyelectrolyte multilayers and propose these as a model system for the eco-corona. The foundation of the eco-corona interacting like a polymer brush with its surrounding may help understand microplastic transport and aggregation in the environment.