Issue 16, 2013

Anomalous chain diffusion in unentangled model polymer nanocomposites

Abstract

We studied unentangled poly(ethylene-alt-propylene) (PEP) in a composite with hydrophobic silica particles as a function of the filler concentration. Our neutron spin echo (NSE) experiments cover both the internal dynamics as well as the center of mass diffusion beyond the Rouse time. The key experimental results are (i) all of the chains are equally mobile, (ii) the basic segmental (Rouse) relaxation rate is unaffected even at highest filler concentrations, and (iii) apparently the obstacles reduce significantly the translational center of mass motion. This happens, even in the case when the particles do not significantly confine the polymer. (iv) A transition from regular to anomalous diffusion in the Rouse regime at the highest particle fractions is clearly evidenced. In order to understand the microscopic mechanisms underlying the experimental observations, we performed coarse grained simulations. We demonstrate that the geometrical confinement only affects the dynamics at a long time scale outside the experimental window and therefore it is not able to explain the results found in the NSE experiments. The consideration of inter-chain interactions, however, results in a significant influence even at shorter times and a quantitative agreement between the experiments and simulations was found. The simulations clearly demonstrate that the interfaces cause a deceleration of the chains in their close vicinity. Then the inter-chain interactions carry this slowing down to the other chains at a time-scale of the Rouse relaxation time. Hence, in the experimental datasets an overall slowing down is observed.

Graphical abstract: Anomalous chain diffusion in unentangled model polymer nanocomposites

Article information

Article type
Paper
Submitted
17 Dec 2012
Accepted
20 Feb 2013
First published
13 Mar 2013

Soft Matter, 2013,9, 4336-4348

Anomalous chain diffusion in unentangled model polymer nanocomposites

G. J. Schneider, K. Nusser, S. Neueder, M. Brodeck, L. Willner, B. Farago, O. Holderer, W. J. Briels and D. Richter, Soft Matter, 2013, 9, 4336 DOI: 10.1039/C3SM27886G

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