A Study of Bare and Grafted Gold Nanorods (AuNRs) with DDLS at Two Different Wavelengths

Polymer-grafted gold nanorod (AuNR) solution is a system of great interest to polymer technology and basic science. AuNRs' known structure and diffusive properties provide a versatile environment for the addition of a polymer and study of a grafted AuNR. Grafting polymer to AuNRs allows to control the system diffusion for variety of applications and for studying fundamental properties of grafted AuNR such as effect of polymer conformation on diffusion of the system. In this project, the structure and dynamics of bare and PMA-grafted AuNRs was characterized by Scanning Electron Microscopy (SEM), Depolarized Dynamic Light Scattering (DDLS), and UV-Vis Spectrophotometry. Using SEM a reliable size distribution of bare AuNRs was obtained, but grafted AuNRs were seemingly a subject to damaging by the electron beam. UV-Vis provided confirmation of the successful grafting. DDLS focused on studying the diffusion of bare and grafted AuNRs. DDLS experiments utilized two separate setups, one with a laser wavelength of 488nm and the other of 637nm. The light scattering differed at these two wavelengths both for the bare and grafted samples, making our DDLS sizing data challenging to interpret. A significant absorption of nanorods, particularly at 637nm, which happens to coincide with the longitudinal surface plasmon resonance (LSPR) of nanorods was a likely contributor to the difference. This work attempts to understand the effect of light absorption at LSPR on DDLS data interpretation for structure and dynamics of bare and grafted AuNRs.