Probing Translational and Rotational Dynamics of Polymer-Grafted Nanorod Solutions

Polymer-grafted gold nanoparticles (AuNPs) are widely studied materials that combine the structural integrity and optical properties of AuNPs with the stabilizing effects of a polymer canopy. The unique properties of AuNPs lead to a variety of applications from drug delivery to biomedical sensing, to catalysis. This project focuses on geometrically anisotropic nanoparticles, specifically gold nanorods (AuNRs). It explores the effects of AuNRs geometry on chain conformation, relaxation dynamics, and macroscopic transport properties of nanorods by measuring rotational and translational diffusion of grafted AuNRs using depolarized dynamic light scattering (DDLS). First, the apparent dimensions of bare AuNRs were deduced from DDLS and compared with SEM measurements. Then AuNRs were grafted with thiol-terminated 10kDa poly(ethylene glycol) (PEG) and characterized with DDLS. Light scattering experiments on AuNRs grafted with PEG have shown an apparent 3-fold increase in hydrodynamic diameter and unchanged hydrodynamic length in comparison to bare AuNRs. The results on AuNRs hydrodynamic dimensions and deduced grafting density of PEG on the AuNRs surface are consistent with basic understanding of grafted polymer chain distribution on the surface of geometrically anisotropic AuNPs.