Influence of polymer topology on rheological behavior and nanoparticle motion in PEO/SiO2 nanocomposite solutions

Abstract

The impact of polymer topology on the rheological behavior of poly(ethylene oxide) (PEO)/SiO<inf>2</inf> mixtures in solution was systematically investigated. Four distinct PEO architectures —linear, four-arm star, eight-arm star, and hyperbranched—were studied to elucidate their influence on nanoparticle (NP) aggregation, dispersion, and bulk viscosity. UV–vis spectroscopy and rheological measurements revealed that polymer topology significantly affects NP aggregation behavior and the viscosity of the resulting solutions. Additionally, the nanoscale relaxation of NPs was examined across different polymer concentrations using X-ray photon correlation spectroscopy (XPCS). A direct correlation was observed between increasing polymer branching and structural disorder in NP arrangements. Hydroxyl end groups in highly branched architectures strongly protonated the silica NP surfaces, reducing the effective surface charge and weakening electrostatic repulsion. Consequently, the excluded volume between NPs decreased, leading to broader distribution of interparticle spacing. The results show that polymer branching had a pronounced effect on NP mobility. While normal diffusive behavior was observed for all samples, the stretched exponential form (β < 1) indicates a distribution of relaxation times. Increasing polymer branching reduced the degree of heterogeneity, with NPs in hyperbranched polymer solutions exhibiting more homogeneous dynamics compared to those in linear and four-armed star polymer solutions. These findings highlight the crucial role of polymer architecture in governing both the structural organization and dynamic properties of NPs in polymeric solutions.