Temperature-Responsive Self-Assembly of Nanoparticles Grafted with UCST Polymer Ligands

Temperature-responsive self-assembly (TRSA) of polymer-stabilized nanoparticles is a promising method that is useful for many applications. Currently, polymers ligands with a lower critical solution temperature are used for TRSA, which requires the use of specific polymersolvent couples. We report a comprehensive study of TRSA of nanoparticles grafted with polymer ligands with an upper critical solution temperature (UCST). Upon cooling the nanoparticle solution below the transition temperature, the nanoparticles assembled in clusters, while upon heating these clusters dissociated into individual nanoparticles. The TRSA was reversible and reproducible. In the heating and cooling steps, the dimensions of nanoparticle clusters were controlled by the superposition of temperature and incubation time. The transition to TRSA was governed by the solvent quality for the polymer ligands and was tuned by varying solvent composition. The utilization of UCST polymer ligands offers an effective method for the preparation of assemblies of polymer-tethered nanoparticles, broadens the range of polymers used for TRSA, and enables control of the degree and temperature of nanoparticle assembly.