Abstract
We measure the center-of-mass diffusion of silica nanoparticles (NPs) in entangled poly(2-vinylpyridine) (P2VP) melts using Rutherford backscattering spectrometry. While these NPs are well within the size regime where enhanced, nonhydrodynamic NP transport is theoretically predicted and has been observed experimentally (2RNP/dtube ≈ 3, where 2RNP is the NP diameter and dtube is the tube diameter), we find that the diffusion of these NPs in P2VP is in fact well-described by the hydrodynamic Stokes-Einstein relation. The effective NP diameter 2Reff is significantly larger than 2RNP and strongly dependent on P2VP molecular weight, consistent with the presence of a bound polymer layer on the NP surface with thickness heff ≈ 1.1Rg. Our results show that the bound polymer layer significantly augments the NP hydrodynamic size in polymer melts with attractive polymer-NP interactions and effectively transitions the mechanism of NP diffusion from the nonhydrodynamic to hydrodynamic regime, particularly at high molecular weights where NP transport is expected to be notably enhanced. Furthermore, these results provide the first experimental demonstration that hydrodynamic NP transport in polymer melts requires particles of size ≳5dtube, consistent with recent theoretical predictions.
Original language | English |
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Pages (from-to) | 1141-1145 |
Number of pages | 5 |
Journal | ACS Macro Letters |
Volume | 5 |
Issue number | 10 |
DOIs | |
State | Published - Oct 18 2016 |
Funding
The University of Pennsylvania team acknowledges funding of this work from the NSF Division of Materials Research through Grant Nos. DMR-1120901, DMR-1210379 (K.I.W.), and DMR-1507713 (R.J.C.). R.J.C. acknowledges funding from the American Chemical Society PRF Grant No. 54028-ND7 and DuPont CR&D. V.B. and K.S.S. acknowledge financial support from the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. We thank J. S. Meth (Dupont) for assistance with molecular weight characterization and C.-C. Lin for transmission electron microscopy.