Temperature-dependent colloidal behavior of polymer-stabilized gold nanoparticles

Polymer-based composites, like polystyrene-gold nanoparticles (PS-AuNPs) are widely used in pharmaceutical and biomedical applications including targeted drug delivery, imaging, biosensing, and photothermal due to their combined plasmonic and structural properties. However, processing conditions significantly influence their structural and functional properties. This study investigates the effects of synthesis temperature on the stability and resuspension behavior of PS-AuNPs, focusing on a range of 78-90 °C. At temperatures below 84 °C, PS-AuNPs maintain stability, forming well-defined pellets after centrifugation and resuspending efficiently. At 86 °C, a coating over the gold nanoparticles was observed via transmission electron microscopy (TEM), which was attributed to the partial softening of polystyrene because of approaching its glass transition temperature regime of around 90 °C. This structural degradation reduced the resuspension efficiency and increased aggregation in high ionic strength environments. Salt aggregation tests showed significant nanoparticle instability at higher synthesis temperatures, as shown by the visible aggregation and sedimentation of the particles in the presence of NaCl.