November 9, 2023 4:00 pm
November 9, 2023 5:30 pm
Simulation and Measurement of Grafted Polymer Dynamics
Mike Hore
Warren E. Rupp Associate Professor
Case Western Reserve University
Polymer brushes are an important class of materials that find uses in a wide range of applications, such as in modulating the mechanical properties of nanocomposites or tuning immune responses to new therapeutics. In this talk, I will describe our recent experimental and computational work investigating the conformation and relaxation dynamics of two types of brush systems (polymer-grafted nanoparticles and molecular bottlebrushes) with neutron scattering techniques and dissipative particle dynamics (DPD) simulations. When grafted to nanoparticles, polymers can adopt a variety of conformations depending on the nanoparticle size/shape and polymer grafting density. At moderate grafting densities, the nanoparticle curvature produces elongated polymer conformations close to the nanoparticle core which transition to ideal conformations as the distance from the nanoparticle core increases. Through selective deuteration, we were able to separately measure the polymer conformation within these regions using small-angle neutron scattering (SANS), and verify that the Daoud-Cotton model for star polymers can accurately describe the structure of the brush. Neutron spin echo (NSE) measurements on the same systems found that the portion of the brush closer to the nanoparticle core exhibits relaxation times that are 2–3 times longer than those in the outer region of the brush. Our DPD simulations show that this effect is due to increased spatial confinement by a higher density of monomers near the nanoparticle core, and agree quantitatively with experimental measurements. In the second portion of this talk, I will discuss neutron scattering measurements of molecular bottlebrushes in solution and compare them to our DPD simulations to better understand the structure and relaxation dynamics of relatively short bottlebrushes. By analyzing the motions of the polymers using proper orthogonal decomposition (POD), we extracted the fundamental monomer displacement patterns (i.e., relaxation modes) that contribute to the motions of monomers. These modes, combined with our simulation results, provide insight into the primary factors that influence bottlebrush relaxation dynamics in solution and help us to interpret neutron spectroscopy measurements.