G. P. Baeza, J. Oberdisse, A.Alegria, Kay Saalwächter, M. Couty, A.-C. Genix.
Depercolation of aggregates upon polymer grafting in simplified
industrial nanocomposites studied with dielectric spectroscopy.
Polymer 73, 131-138 (2015).
The dynamics of polymer and filler in simplified industrial silicaestyreneebutadiene nanocomposites
(silica Zeosil 1165 MP, volume fraction 0-21%v) have been studied with broadband dielectric spectroscopy
(BDS) and nuclear magnetic resonance (NMR). The fraction of graftable matrix chains was varied
from 0 to 100%D3. The introduction of silica nanoparticles is shown to leave the segmental relaxation
unaffected, an observation confirmed by the measurement of only a thin (some Angstroms thick)
immobilized layer by NMR. The low-frequency measurements are resolved in two distinct dielectric
MaxwelleWagnereSillars (MWS) processes of different behavior with respect to changes of large-scale
silica structures induced by variations of filler fraction and grafting. It is found that increasing grafting
leaves the first MWS-process unaffected, while it decreases the strength of the (slower) second MWS by
about a decade. At constant silica volume fraction, this indicates depercolation of the filler, thereby
providing a microscopic explanation of the evolution of rheological reinforcement. The sensitivity to
large-scale reorganizations together with a characterization of local polymer dynamics provides insight
over many length- and time-scales into structure and dynamics of nanocomposites, and thus the physical
origin of the reinforcement effect.