Directional Self-Assembly of Nanoparticles Coated with Thermoresponsive Block Copolymers and Charged Small Molecules

Herein, we report the directional stimuli-responsiveself-assemblyof gold nanoparticles (AuNPs) coated with a thermoresponsive blockcopolymer (BCP), poly(ethylene glycol)-b-poly(N-isopropylacrylamide) (PEG-b-PNIPAM) andcharged small molecules. AuNPs modified with PEG-b-PNIPAM possessing a AuNP/PNIPAM/PEG core/active/shell structureundergo temperature-induced self-assembly into one-dimensional (1D)or two-dimensional (2D) structures in salt solutions, with the morphologyvarying with the ionic strength of the medium. Salt-free self-assemblyis also realized by modulating the surface charge by the codepositionof positively charged small molecules; 1D or 2D assemblies are formeddepending on the ratio between the small molecule and PEG-b-PNIPAM, consistent with the trend observed with the bulksalt concentration. A series of charge-controlled self-assembly atvarious conditions revealed that the temperature-induced BCP-mediatedself-assembly reported here provides an effective means for on-demanddirectional self-assembly of nanoparticles (NPs) with controlled morphology,interparticle distance, and optical properties, and the fixation ofhigh-temperature structures.

Automated summary

Here, we report the directional stimuli-responsive self-assembly of gold nanoparticles (AuNPs) coated with a thermoresponsive block copolymer (BCP), poly(ethylene glycol)-b-poly(N-isopropylacrylamide) (PEG-b-PNIPAM), and charged small molecules. The temperature-induced self-assembly resulted in one-dimensional (1D) or two-dimensional (2D) structures in salt solutions, with the morphology dependent on the ionic strength of the medium. Salt-free self-assembly was achieved by modulating the surface charge using positively charged small molecules, with the assembly type determined by the ratio between the small molecule and PEG-b-PNIPAM. This study demonstrates an effective approach for on-demand directional self-assembly of nanoparticles (NPs) with controlled morphology, interparticle distance, and optical properties.