Influence of the Bound Polymer Layer on Nanoparticle Diffusion in Polymer Melts

Area of Science:

• Polymer Physics
• Materials Science
• Nanotechnology

Background:

• Theoretical models predict enhanced, nonhydrodynamic nanoparticle (NP) transport in polymer melts when NP size is comparable to the polymer tube diameter.
• Experimental verification of these predictions is crucial for understanding NP dynamics in complex polymer systems.

Purpose of the Study:

• To investigate the center-of-mass diffusion of silica nanoparticles (NPs) in entangled poly(2-vinylpyridine) (P2VP) melts.
• To determine if NP diffusion follows predicted nonhydrodynamic behavior or the classical Stokes-Einstein relation.

Main Methods:

• Utilized Rutherford backscattering spectrometry to measure the diffusion of silica NPs in P2VP melts.
• Analyzed NP diffusion in relation to NP size, polymer molecular weight, and polymer tube diameter.

Main Results:

• Observed that silica NP diffusion in P2VP melts is accurately described by the hydrodynamic Stokes-Einstein relation, contrary to nonhydrodynamic predictions.
• Found that an effective NP diameter, larger than the bare NP size, is strongly dependent on P2VP molecular weight, indicating a bound polymer layer.
• The bound polymer layer thickness is approximately 1.1 times the polymer radius of gyration (Rg).

Conclusions:

• A significant bound polymer layer on NPs augments their hydrodynamic size in polymer melts with attractive polymer-NP interactions.
• This augmentation transitions NP diffusion from the nonhydrodynamic to the hydrodynamic regime, particularly at higher polymer molecular weights.
• Hydrodynamic NP transport in polymer melts requires particle sizes exceeding approximately 5 times the polymer tube diameter.