In-Situ Monitoring Polymer-graft Functionalization on Gold Nanoparticles and Influences on Assembly Formation

Controlled assemblies of polymer grafted nanoparticles can lead to a unique class of material with distinct advantages due to the programmability and diversity endowed from polymer-based-ligands. Surface functionalization of nanoparticles (NPs) with polymer-based ligands plays a critical role in controlling the effective size and ‘interaction softness’. To this end, it is requisite to quantity the attached polymer ligands. Here we present the (in situ) proton nuclear magnetic resonance (¹H NMR) study on the ligand exchange of oleylamine by thiol end-functionalized polystyrene as a function of the ligand concentration and particle size on Au NPs. As the extensive overlap of the polymer ligands impede the direct evaluation, we examine the pristine chemical shifts of the oleylamine to characterize the ligand modification. We show that the surface functionalization efficacy depends on the ligand/particle ratio, size of NPs and molecular weight of the polymeric ligands. These quantitative studies enabled us to investigate the influences of the ligand modification and solvent quality on the ordering of the self-assembled polymer grafted nanoparticles with a focus on a polycrystalline assembly to hexagonally ordered superlattice transition.