Collective Nanoparticle Dynamics Associated with Bridging Network Formation in Model Polymer Nanocomposites

Benjamin M. Yavitt, Daniel Salatto, Yuxing Zhou, Zhixing Huang, Maya Endoh, Lutz Wiegart, Vera Bocharova, Alexander E. Ribbe, Alexei P. Sokolov, Kenneth S. Schweizer, Tadanori Koga

Research output: Contribution to journalArticlepeer-review

Abstract

The addition of nanoparticles (NPs) to polymers is a powerful method to improve the mechanical and other properties of macromolecular materials. Such hybrid polymer-particle systems are also rich in fundamental soft matter physics. Among several factors contributing to mechanical reinforcement, a polymer-mediated NP network is considered to be the most important in polymer nanocomposites (PNCs). Here, we present an integrated experimental-theoretical study of the collective NP dynamics in model PNCs using X-ray photon correlation spectroscopy and microscopic statistical mechanics theory. Silica NPs dispersed in unentangled or entangled poly(2-vinylpyridine) matrices over a range of NP loadings are used. Static collective structure factors of the NP subsystems at temperatures above the bulk glass transition temperature reveal the formation of a network-like microstructure via polymer-mediated bridges at high NP loadings above the percolation threshold. The NP collective relaxation times are up to 3 orders of magnitude longer than the self-diffusion limit of isolated NPs and display a rich dependence with observation wavevector and NP loading. A mode-coupling theory dynamical analysis that incorporates the static polymer-mediated bridging structure and collective motions of NPs is performed. It captures well both the observed scattering wavevector and NP loading dependences of the collective NP dynamics in the unentangled polymer matrix, with modest quantitative deviations emerging for the entangled PNC samples. Additionally, we identify an unusual and weak temperature dependence of collective NP dynamics, in qualitative contrast with the mechanical response. Hence, the present study has revealed key aspects of the collective motions of NPs connected by polymer bridges in contact with a viscous adsorbing polymer medium and identifies some outstanding remaining challenges for the theoretical understanding of these complex soft materials.

Original languageEnglish (US)
Pages (from-to)11501-11513
Number of pages13
JournalACS Nano
Volume15
Issue number7
DOIs
StatePublished - Jul 27 2021

Keywords

  • PRISM theory
  • collective nanoparticle dynamics
  • mode-coupling theory
  • polymer bridges
  • polymer nanocomposites
  • x-ray photon correlation spectroscopy

ASJC Scopus subject areas

  • General Engineering
  • General Physics and Astronomy
  • General Materials Science

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