Temperature modulated polymer nanoparticle bonding: A numerical and experimental study

Abstract In this research, we investigated the impact of nanoparticle adhesive properties on the size of micro-clusters formed during shear-induced aggregation at different temperatures. To precisely control particle adhesion, we used nanoparticles with a core-shell structure, where the core is composed of polymethyl methacrylate and the shell is composed of a combination of polymethyl methacrylate and polybutylacrylate. Due to significantly different glass transition temperature (Tg) of these polymers, the core act as a hard-sphere, while the presence of polybutylacrylate in the shell, with a glass transition temperature of 50 °C, gives the surface mechanical softness upon increasing temperature. We observed that the size of the aggregates grow significantly when the temperature rises above Tg, indicating an increase of adhesive force between the nanoparticles. Under these conditions, the surface of the nanoparticles exhibits a transition from plastic to viscous behavior that allows core-shell nanoparticles to bond physically upon contact in a controlled coalescence effect. To further investigate the micro-mechanical behavior of the micro-clusters during aggregation, a numerical study of a simple shear flow setup using CFD-DEM with a customized particle interaction model was carried out. This model has the capability to describe non-contact as well as contact forces present in colloidal systems. Depending on the system temperature, the model can simulate either elastic, elastic-plastic or viscoplastic deformation between the interacting nanoparticles. Using this feature, it is demonstrated that it is possible to reproduce the experimentally observed growth in aggregates with temperature rise by simulating an increase in adhesion using primary particle mechanical parameters. Furthermore, these results clearly demonstrate the direct relation between surface properties of the nanoparticles with the macroscopic behavior of the colloidal system.