Elucidation of Polymer-Grafted Nanorod Transport Behaviors and Brush Structure

Extremely small particles that have long molecules called polymers attached to their surfaces are used in technologies ranging from advanced materials to medical diagnostics. Designing these materials requires scientists to understand particle size, shape, and surface structure. However, the necessary characterization techniques require specialized instrumentation and expertise. This project will develop a faster and more accessible method for characterizing this class of particles using a combination of computer simulations and experimental measurements. The new approach will be used to determine how the particle shape influences the structure and properties of polymers on its surface. The insight will be used to design advanced materials and test predictions of polymer behavior on curved surfaces. The project will also exploit the unique optical properties of tiny gold rods to study how particle motion changes within materials that mimic biological materials such as mucus. The results will provide new tools to study these particles, deepen understanding of their properties, and advance knowledge of how they move through soft materials used in drug delivery, disease treatment, and advanced manufacturing. Polymer-grafted nanoparticles are important in modern technologies. While electron microscopy and X-ray/neutron scattering are powerful techniques for characterizing such systems, they suffer drawbacks including limited sampling volumes, low throughput, and challenges in characterizing complex anisotropic particles. Dynamic light scattering is a fast, high-throughput bench-top characterization technique that addresses many of these limitations by measuring particle diffusion but is typically restricted to spherical particles. Depolarized dynamic light scattering can characterize nanorods by measuring both rotational and translational diffusion; however, it relies on precomputed shape functions that do not account for surface-grafted polymers. Consequently, current theory cannot characterize polymer-grafted nanorods. This project will combine depolarized dynamic light scattering experiments, computer simulations, and theoretical modeling to (1) determine how grafted polymers influence the translational and rotational diffusion of polymer-grafted gold nanorods and develop new shape functions for their characterization; (2) utilize these new shape functions to investigate the effects of surface geometry and curvature on polymer brush structure and properties, providing experimental tests of key theoretical predictions; and (3) exploit surface plasmon resonances in gold nanorods to understand how polymer-grafted nanorod diffusion is affected by confinement within hydrogel materials. The resulting advances will establish new capabilities for the rapid characterization of anisotropic polymer-grafted nanoparticles, provide insight into polymer behavior at curved interfaces and transport in polymer networks, and produce open-source computational tools for the research community. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.