Dynamics of Polymer-Grafted Nanoparticle Suspensions

Polymer-grafted gold nanoparticles (AuNPs) are a widely studied class of material that combine polymer and colloidal physics. Gold nanoparticles provide structural integrity and impart desirable optical properties; polymers grafted to the nanoparticle surface provide stability in a colloidal suspension. Their unique physical properties give rise to a broad range of applications ranging from drug delivery, to biomedical sensing, to catalysis. This poster explores the dynamics of polymer-grafted nanoparticle suspensions from two perspectives: (1) evaluating the effects of anisotropy on chain dynamics, and (2) determining how polymer molecular weight controls the colloidal stability of AuNP solutions. We explore the effects of nanorod geometry on chain conformation, relaxation dynamics, and rotational and translational diffusion using depolarized dynamic light scattering (DDLS). We observe an increase in the hydrodynamic dimensions of nanorod AuNPs grafted with 10 kDa thiolated PEG, with a larger increase in the radial direction than in the longitudinal direction. This increase is consistent with our understanding of grafted polymer chain distribution on the surface of geometrically anisotropic AuNPs. Similarly, we modulate the rate of aggregation through grafting and characterize aggregation kinetics in solution. We can examine the effect of different molecular weights of polymer on any structural hysteresis in the relationship between particle size and temperature. Additionally, a DLS temperature ramp was performed to explore aggregation and dispersion behavior. DLS revealed a kinetic effect from slow aggregation for rods functionalized with a 57 kDa thiolated polystyrene and in spheres functionalized with a 233 kDa polystyrene. Future experiments will characterize the effect of varying both polymer molecular weight and nanorod radius on chain conformation and the diffusive properties of the grafted nanoparticles. Additionally, measurements will explore the effect of varying temperature on the absorbance of UV light by the particles, to tailor the aggregation kinetics to optimize aggregation in the presence of environmental contaminants and generate a novel class of nanoparticle-based sensors.