Viscoelasticity of solvent-free polymer-grafted nanoparticles

Abstract

Polymer-grafted nanoparticles (PGNs), which synergistically combine nanoparticle motion and polymer relaxation dynamics, exhibit unique hybrid viscoelastic characteristics crucial for fundamental scientific understanding and advanced material design. In this study, we employed dissipative particle dynamics (DPD) simulations coupled with nonequilibrium oscillatory shear techniques to systematically investigate the rheological properties of solvent-free PGNs with moderate grafting density. Our simulation results reveal a strong dependence of viscoelastic behavior on two key structural parameters: grafted polymer chain length and nanoparticle radius. Specifically, PGNs with shorter grafted chains or larger nanoparticles demonstrate a distinctive low-frequency elastic plateau attributed to the cage effect arising from their close-packed structures. Conversely, systems with longer grafted chains or smaller nanoparticles exhibit the formation of string-like structures, resulting in anisotropic viscoelastic responses. At higher frequencies, we observed a characteristic loss tangent peak corresponding to the collective motion of PGNs, whose position shifts with variations in grafted chain length and nanoparticle size. Furthermore, the frequency sweep curves consistently showed a reproducible downturn in loss modulus. These findings provide fundamental insights into the structure-property relationships of PGNs and offer valuable guidance for designing advanced nanocomposites with tunable dynamic moduli.