# Soft interactions modify the diffusive dynamics of polymer-grafted nanoparticles in solutions of free polymer

## TL;DR

This study reveals that soft interactions in polymer-grafted nanoparticles lead to unique diffusive behaviors in polymer solutions, deviating from classical models based on bulk viscosity and hard sphere assumptions.

## Contribution

It demonstrates how soft interactions alter nanoparticle diffusion, showing decoupling from bulk viscosity and non-universal diffusivity scaling in polymer solutions.

## Key findings

- Grafted nanoparticle dynamics decouple from bulk viscosity.
- Diffusivities do not follow a master curve as a function of normalized length.
- Soft interactions enable faster diffusion than predicted by bulk rheology.

## Abstract

We examine the dynamics of silica particles grafted with high molecular weight polystyrene suspended in semidilute solutions of chemically similar linear polymer using x-ray photon correlation spectroscopy. The particle dynamics decouple from the bulk viscosity despite their large hydrodynamic size and instead experience an effective viscosity that depends on the molecular weight of the free polymer chains. Unlike for hard sphere nanoparticles in semidilute polymer solutions, the diffusivities of the polymer-grafted nanoparticles do not collapse onto a master curve as a function of normalized length scales. These results suggest that the soft interaction potential between polymer-grafted nanoparticles and free polymer allows polymer-grafted nanoparticles to diffuse faster than predicted based on bulk rheology and modifies the coupling between grafted particle dynamics and the relaxations of the surrounding free polymer.